Dr David Martin

Thitiphorn Bianca

G Eorgia

D R A Ndrea Also

D R K Ais

D R Etienne

R eka, G hizlene, W im onsiri, D ebsouri, M artin D R Jonas

Océane, Clém ent D R Tan

Dr Marie Cordier

Vincent Dorcet

Dr Pierre Dixneuf

Christian Bruneau

First of all, I would like to express my gratitude to my supervisors Dr. Jeanne Crassous

General introduction

-conjugated materials have recently emerged as a promising direction in materials science due to their specific interaction with CP-light and the potential of the latter in several domains of applications such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and magnets. [1] While extensive researches have been focusing on organic chiral dyes with closed-shell electronic configuration, a few attention has been paid on their open-shell counterparts (radicals), presumably because of their reactivity and stability issues. This Thesis has aimed to develop novel intrinsic chiral radicals based on carbazole backbone. We explored a new molecular design of intrinsically persistent chiral organic radicals via a SOMO-HOMO level inversion (SHI) process, which allowed us to highlight certain key parameters governing the stability of the obtained radical species. We have extended this approach to various cationic and neutral radical structures, resulting in the generation of novel and relatively stable cationic and neutral chiral monoand di-radicals, presenting both fundamental and promising directions in opto-electronic applications. [2][3][4][5][6] Chapter 1 highlighted the generality of chirality and radicals; the related applications in material fields, and the state-of-the-art of chiral radical molecules.

Chapter 2 described further insight regarding the generality of the uncommon electronic configuration of the radicals, namely SOMO-HOMO inversion (SHI), related experimental results to rationalize the presence of SHI, and selected examples of organic radical with SHI. Then, the synthetic revisiting of BICOL backbone and further functionalization towards 128 and 129 bearing different chirality, namely axial vs. helical, have been described. Their relative differences between axial and helical chirality were studied by photophysical, chiroptical, and electrochemical properties together with the formation of their corresponding monoradical. The unprecedented stability of 128 allowed us to rationalize further inside regarding the stabilization factor, which is an interplay between SHI and subtle electronic coupling between the two carbazole fragments. Such findings notably allowed us to further design and isolate stable chiral diradical 130 presenting near-infrared chiroptical properties and nearly degenerated singlet-triplet energy transition. Chapter 3 described the stabilization approach for the unstable helical monoradicals 129 and 131. Two tetracarbazoles 132 and 133 have been described through their synthesis and characterization. Their difference in photophysical and chiroptical properties reveals the importance of the molecular structure in solution and the related stability of their corresponding monoradicals.

The presence of the NIR band allowed us to investigate further the impact of the solvent polarity on the NIR absorption, which presented, for the first time, ECD sign inversion as a function of the solvent polarity. Furthermore, such a high stability of these monoradicals allowed us to prepare diradical with an antiferromagnetic singlet ground state with larger singlet-triplet energy transition compared to 132 . Surprisingly, the diradical 132 still presented the SHI even in a diradical state, which played a role in radical stabilization. Once again, the observed SHI in the diradical state of 132 represents a rare example of diradical with such a unique electronic configuration.

Chapter 4 described the exploration of the novel carbon-centered based radicals with a possibility to possess SHI and chirality by a combination with carbazole backbone, namely indenocarbazole. The synthesis and characterization of this series have been described along with the attempts to generate mono-and di-radicals based on the molecular design. Chapter 1: Introduction: chirality and radicals

Summary

This first chapter will consist in an introduction on chirality, some features in materials applications followed by an introduction on some aspects of organic radicals i.e., electronic configuration, spin-spin interaction, stabilization of organic radicals, and their feature in diverse fields of materials. This general information is related to the project involved in the manuscript. In the last part of this chapter, an overview of chiral radical systems will be presented.

Chirality

Chirality (from the Greek word refers to an object that is non-superimposable to its mirror-image such as human hands (Figure 1-1). [1] An object can be considered as chiral once it does not have any improper axis of symmetry Sn. [2] Chirality exists in every scale from the elemental particles to the spiral structure of the galaxies. In chemistry, two molecules with identical chemical formula are constitutional isomers.

Isomers possessing the same atomic constituents but in a different spatial arrangement are called stereoisomers. The pairs of stereoisomers are -imaged otherwise they which can be of different nature such as point (central), axial, planar, or inherent to the molecule, such as propeller-like, or helical (Figure 12). Point chirality is often referred to a sp 3 carbon bearing four different substituents (note: heteroatoms can display point chirality, i.e. N, P, S to name a few). To describe a difference between the two enantiomers, specific notations were defined using the Cahn-Ingold-Prelog (CIP) rule as R (clockwise)/S (anticlockwise) for point chirality. [3] From point chirality, it is possible to observe chirality from non-asymmetric carbon with a spatial arrangement, which can be axial chirality from sterically hindered biarylic systems (defined as Ra/Sa or P/M; see chapter 2 for further details), planar chirality obtained from the two sides of a prochiral plane (defined as Rp/Sp), or propeller and helical chirality from an inherent helical shape like helicenes (defined as P/M). The axial and helical chirality will be developed extensively all along the manuscript with a chiral specific notation as R/S or P/M. The two enantiomers of a chiral molecule cannot be distinguished from each other through their physicochemical properties in solution (except their chiroptical properties, vide infra). The mixture between the two enantiomers can be characterized as follow:

-If there is the presence of only a single enantiomer, the compound is considered as -If there is the presence of both enantiomers in a 1:1 ratio, the compound is considered as -If a mixture of enantiomer contains any ratio rather than 1:1 or enantiopure, the mixture is considered as a compound in enantiomeric excess (ee), which defines as equation 1:

(1) and are the quantity of the two enantiomers, the enantiomeric excess is 0 for racemic mixture and 100 for an enantiopure compound. For example, 90% ee means that the mixture contains 95% of the major enantiomer and 5% of the other. [1] Chirality has widely attracted attention of the scientific community, especially because of the homochirality of life. Indeed, the essential building blocks for a living organism such as amino acids or carbohydrates exist under only one single enantiomeric form: Fischer L-configuration for amino acids and D configuration for sugars. Investigations in astrochemistry and magnetochiral dichroism (MChD) proposed a possible mechanism of the homochirality of life. [4] The circularly polarized (CP) light irradiation has attracted interest as an essential trigger, which governs the chirality in the system. For instance, studies on the irradiation of a racemic mixture of amino acid derivatives with CP far-UV light under the outer space condition showed a preference for one enantiomer up to 10% ee. [5][6][7][8][9] On the other hand, the MChD is related to the magnetic field, thus the ee value due to MChD should be high under the influence of intense magnetic fields liked neutron stars. [10] MChD-based photochemical reactions of aromatic amino acids may induce asymmetric reactions in the space.

Parallelly, the chirality involvement has been highlighted in many biological processes. The impact of stereochemistry on drugs has been observed through several human health tragedies such as thalidomide (Figure 123). In the 50s, this compound was responsible for the worldwide birth deformities, namely the Softenon disaster, due to pharmaceutical commercialization of the drug under racemic form. Thalidomide has one asymmetric carbon at the isoindole group, which delivers different effects between R and S enantiomers. R-thalidomide has an antiemetic and hypnotic sedative effect, while the S enantiomer has a teratogenic effect. This observation significantly enhanced the development of chiral synthesis and analysis. For instance, X-ray diffraction, nuclear magnetic resonance (NMR), and infrared spectroscopy (IR) have been developed for chiral analysis in solid states. The interaction between a chiral solution with external sources also allows us to discriminate them by some techniques, such as HPLC with chiral stationary phases (chiral HPLC), optical rotation dispersion (ORD), electronic circular dichroism (ECD), the latter being the most widely used chiroptical spectroscopy (vide infra). In addition, asymmetric synthesis has also attracted attention due to its importance in pharmaceutical and cosmetic industries, which directly transforms a prochiral substrate into a single enantiopure compound and offers more efficient synthetic routes. The importance of chirality in the biological context has been well established and continues to be more intensive. More recently, the chiral materials have brought further opportunities due to i) the specific interaction of chiral molecules with circularly polarized (CP) light and ii) the particular relation of chirality with magnetism and charge conduction, which are highly promising added values to molecular materials in future technologically devices.

Circularly polarized light can be described as two planes of polarized waves with equal

Once both planes constantly rotate to the travel direction, it results in a helix along the propagation direction, which can be either counterclockwise or clockwise to the receptor, namely left circularly polarized (LCP) light and right circularly polarized (RCP) light, respectively (Figure 1234). [1,11] At the molecular level, the interaction of CP-light with a chiral nonracemate can be characterized using chiroptical spectroscopies resulting in the specific responses opposite in sign for the two enantiomers. Chiroptical spectroscopies directly detect an interaction between chiral nonracemate with CP-light. The latter may be classified according to the frequency or wavelength range of resonance including electronic chiroptical spectroscopies (UV-vis-NIR range), electronic circular dichroism (ECD) and circularly polarized luminescence (CPL), and vibrational chiroptical spectroscopies (IR range) such as vibrational circular dichroism (VCD) and raman optical activity (ROA). [1,12] In addition to these chiroptical spectroscopies, ORD is also a classical chiroptical spectroscopy technique to determine a variation in the optical rotation of a substance in a function of wavelength, and optical rotation (OR) determines an interaction of chiral non-racemates with linearly polarized light in transparent media. In this thesis, the main chiroptical spectroscopies will be focused only on ECD and CPL.

Electronic circular dichroism (ECD) is defined as the difference in molar absorption coeffi -and right-CP light for chiral nonracemate compounds. ECD response is mirror-image for a couple of enantiomers, and its value given by equation ( 2) also often probed by the absorption dissymmetric factor (equation 3) for intrinsic quantification (Figure 1-5, topleft).

ECD has been succcessfully used for determining absolute configurations of chiral compounds. [12] For instance, carbo [6]helicene (H6), which represents helical chirality, has an intense activity in ECD (Figure 1-5, bottom). The spectrum displays characteristic bisignate signal; a negative one at about 250 nm (for the (P)-H6 -100 --200 M -1 cm -1 ) and a positive one around 330 nm (for the (P)-H6 +100 -200 M -1 cm -1 ). [13] The M enantiomer depicted a mirror-image spectrum to the P. The bisignate signal observed from ECD in H6 could be used to determine the absolute configuration of a new helicenic system. Binapthyl system with axial chirality is also an ECD-active compound. In fact, the ECD of binaphthyl system is dominated by exciton coupling and displays characteristic bisignate signature (see details in chapter 2). For instance, the spectrum of BINOL displays characteristic mirror-image spectra in the range between 220-330 nm; with a +80 to -150 M -1 cm -1 for the Ra enantiomer) +10 M -1 cm -1 for the Ra enantiomer). Emissive chiral molecules can also display circularly polarized luminescence (CPL). CPL quantifies a difference in the emission intensity between left and right CP light for a nonracemate mixture upon unpolarized light excitation. The luminescence dissymmetric factor (equation 5)

is defined in the same manner as (Figure 1-5, top-right). Similar to ECD, CPL signals from a couple of pure enantiomers are the most intense and mirror-image.

The interaction of chiral molecules with CP light in both absorption and emission raises new opportunities to several applications such as CP-organic light-emitting diodes (CP-OLEDs), CP-photodetectors, chiral-cryptography, and bioimaging displaying some advanced functions compared to conventional devices. [2,11,14] For instance, in OLEDs display, it is common to use antiglare filters, which exploit the physics of CP light to eliminate glare from external light sources, for instance, sunlight (Figure 1-6a). However, this additional layer decreases the system efficiency by removing approximately 50% of the nonpolarized light emitted from the OLED pixel due to reflection. [15][16] Using OLED with chiral emissive molecules will emit directly the CP light and enhance overall efficiency without the use of any filter. The study on chiral emitting materials has been devoted to several molecular classes from chiral conjugated polymers, liquid-crystals, organometallic complexes, and small organic molecules. [16] The latter have attracted attention thanks to their structure and ease of functionalization. For instance, the helicene derivative 1 displays high CPL intensity with glum up to 3-4 10 -2 in solution, with the helicene having an important role in the exciton coupling process (Figure 1-6b). [17] With such high chiroptical properties, the preparation of CP-OLED was successfully fabricated with compound 2b, which displayed high electroluminescence dissymmetric factor (gEL 8 10 -3 , Figure 1-6c and 1-6d, the decrease may come from reflection process inside the device). Another approach is the use of a chiral perturbation strategy associated with a thermalactivated delayed fluorescence (TADF) moiety. [18] For instance, the binaphthol derivative 3 showed high PLQY (up to 74%) associated with CPL activity (|glum| up to 1. 3 10 -3 ). The authors succeeded to fabricate CP-OLED using compound 4, which afforded gEL 1 10 -3 . [19] These two recent examples have proven the potential of chiral emitting compounds for CP-OLEDs application and are under intense development.

Interaction of the CP light with chiral molecules can also exploit additional aspects. For instance, chiroptical switches can respond to several stimuli such as pH, redox potential, or light.

Many recent studies have focused on helicene-based chiroptical switches taking advantage of their intense chiroptical response. Although the switching function of helicene derivatives does not change the helicene structure core, the redox tuning of helicene could be performed thanks to the substituents around helicene or metallic centers. [20][21] One particular example is the iron-based helicene 5 (Figure 1234567). [22] Upon oxidation of the iron centers, a drastic change in the system reversible. The chiroptical switching of this molecule may be useful for fiber optics telecommunication and secure transmission via encryption using chiral molecules. Chirality and magnetism have a close relationship especially for their interaction with light.

In principle, the magnetic field can induce molecules to differentially absorb between left-and right-CP light in the medium. This phenomenon is known as Faraday effect or magnetic circular dichroism (MCD, Figure 1-8a). [23][24] Chiral molecules can display a cross effect of natural circular dichroism and magnetic circular dichroism upon action of a magnetic field and an unpolarized light. This phenomenon is known as magneto-chiral dichroism (MChD). [10,[25][26] MChD has been studied so far on a limited number of chiral molecular systems. [27][28] For instance, helicene-based Yb complex 6

was recently reported as an investigation of the MChD phenomenon through NIR light absorption (Figure 1-8b). This observation provides a possibility to use MChD materials as an optical readout of magnetic data with unpolarized light. Furthermore, as described above, the MChD provides a possible mechanism regarding the origin of the homochirality of life (vide infra). Chiral molecules provide a unique electronic response with the magnetic field. Chiralconductive materials have a specific conductivity related to their electronic resistance and direction of charge conduction, so-called electrical magneto-chiral anisotropy (eMCA). [29][30] Similarly, the other important one is chiral induced spin-selectivity (CISS), which is the ability of chiral molecules to selectively filtrate the electrons depending on their spin state (Figure 123456789). [31][32][33][34][35][36][37] One of the particular examples with the CISS effect was realized in water-splitting reaction since the dihydrogen molecule from the reduction half-reaction of water splitting has attracted attention as a future energy source. However, the oxidation half-reaction usually requires a significant overpotential and reduces overall efficiency. [38] Meijer, Naaman et al reported that a lower overpotential can be achieved in the water oxidation reaction in a photoelectrochemical cell by spin alignment control using electrode coated with chiral Zn-porphyrin 7a. [39][40] The electrode coated with the helical assemblies reduced significantly the overpotential of water oxidation by 0.5 V, leading to an overpotential of only 0.0-0.2 V (Figure 1-9d). They suggested that the decrease of overpotential can be occurred via two different mechanisms. First, the spin-selection from 3 O2 (spinaligned) ground state instead of the 1 O2 (spin antiparallel) species (Figure 1-9b). Second, spin controlled in chiral systems can circumvent the formation of the possible side product such as H2O2

(Figure 1-9e). This important application illustrated the importance of the CISS effect, and it was further realized across a range of scientific fields, including catalysis, enantio-separation, spintronics, long-range electron transfer, and bio-recognition. [41] Chiral organic materials provide opportunities and promising impact on advanced technologies thanks to their specific interaction with light and magnetic fields. Toward this endeavor, extensive research has been devoted to chiral organic molecules with closed-shell electronic structures. Nevertheless, a few attention has been given to their open-shell counterparts (radicals) due to their chemical and configurational instability. Chiral molecules with open-shell electronic structures may bring unique chiroptical responses, especially in the visible and NIR-region, conductivity, and magnetic response. Furthermore, in the presence of the spin, chiral open-shell molecules may give further properties such as eMCA, MChD, and CISS (vide supra), which could bring new opportunities to the advanced material technologies.

Radicals and applications i. Definition

Organic radicals are molecular systems, with an open-shell electronic configuration, involving of one or more unpaired electrons. They are usually unstable and subsequently react with the surrounding molecules through hydrogen abstraction, oligo-/polymerization, disproportionation, or recombination to satisfy their valency. [42][43] Nevertheless, several radicals have been prepared, isolated, and characterized using photophysical and magnetic measurements. [44] Gomberg set a breakthrough discovery with the persistent triphenylmethyl radical 8, in which the three phenyl groups stabilized the radical center to some extents from any side reaction. [45] Other known stable radicals are nitroxide ones, with the most well-known commercial compound of this class being 2,2,6,6-tetramethyl-piperidin-N-oxyl radical (TEMPO 9). This compound is widely used in several applications such as a biological probe, radical trap, organic synthesis, and polymerization mediator. [46] In addition, phenalenyl 10, a nanographene derivative, is another stable radical with a potential for materials science applications. [47] As aforementioned, organic radicals have unique photophysical and magnetic properties resulting from their specific electronic configuration.

ii. Electronic configuration

All of the radicals bring unique properties due to the presence of the unpaired electron(s).

These systems with one unpaired electron are called radical, free radical, or monoradical, depending on user purpose. [48] Radical species possess a molecular orbital containing only a single electron namely singly occupied molecular orbital (SOMO, Figure 1234567891011). The electron into the SOMO level can be aligned either parallel ( spin, ms = +1/2) or anti-parallel ( spin, ms = -1/2) under the an applied magnetic field (H). The spin multiplicity (2S+1) of monoradicals is doublet (2). Unpaired electrons can be detected using electron paramagnetic resonance (EPR).

Application of a magnetic field (H) with adjusted frequency ( ) in the instrument enables energy as and states (Figure 1-11, right). This energy difference is given by equation 6, where ge is the Landé g-factor (ge = 2.0023 for free-electron: approximately 330-340 mT, X-band), e is the Bohr magneton (9.27 × 10 -24 J T -1 ) and H is the strength of the applied magnetic field.

It is noteworthy to mention that some research uses the name of electron spin resonance (ESR), which is common for organic radicals. In principle, both EPR and ESR are the same measurement with different systems. Thus, we will use the term EPR throughout this manuscript.

iii. Diradicals

Beyond the simple radical system, diradicals and polyradicals are of particular interest since they can adopt several spin states related to the interaction between the two-or more-unpaired electrons. These classes of molecules are not only reaction intermediates, but they are highlighted as candidates for further development of spintronics. In this part, we will describe only diradicals, which are the simplest polyradical system. Since diradical systems have two unpaired electrons, the foremost consideration will be the interaction between these two free electrons. According to the IUPAC Gold Book, the encyclopedia for chemical terms, diradicals are distinguished into three groups, namely biradicals, diradicals, and diradicaloids. [49] Biradicals are the diradicals in which the two electrons are too far from each other to significantly interact and act therefore independently or nearly independently, which can be simply identified as two monoradicals in the system. In some sense, the electron exchange interaction (J S-T) of these two electrons is negligible. Thus, the EPR signature of biradical should be the same as monoradical (Figure 1 Considering the two possible spin states of diradicals, when the two free-electron occupy nonbonding molecular orbitals, there are six possible electronic configurations as shown in Figure 1-14. The first two are triplets, while the others are considered singlets. For diradicals, the most half-filled for avoiding electronic repulsion. After fulfilled both electrons, theoretically, triplet electronic configuration should be the ground state electronic configuration for diradicals. The singlet-S-T) can be calculated from the electron exchange interaction (J) by equation 7. A positive value indicates the nature triplet ground state, while a negative value indicates the singlet ground state one. ( 7) As aforementioned, EPR can prove the existence of triplet diradical by the half-field transition (for organic radicals, the half-field transitions are generally located around 150-200 mT).

The intensity of the EPR signal at different temperatures can be also used for determining the nature of the diradical spin state due to the thermal equilibrium between singlet and triplet states.

Thus, the plot between the product of intensity (I) and temperature (T) vs temperature (T) should deviate from linearity (doublet signal, Figure 123456789101112131415). The plot of triplet species diverges upwards compared to the paramagnetic linear one while the singlet species diverge oppositely. The behavior of these two diradicals can be fitted using the Bleaney-Bower equation (equation 8). [50] The curve fitting reveals exchange integration value (J S-T (2J).

(

) 8
Bleaney-Bowers equation where I is absolute curve area from EPR spectrum in (a.u.), T is the temperature in kelvin, C is J is an exchange integration value, k is Boltzmann constant (1.94 × 10 -3 kcal mol -1 ), A is baseline adjusted coefficient. It is noteworthy to mention that the Bleaney-Bowers equation is also applied to SQUID magnetometry. [51][52] The intensity of EPR is qualitatively comparable to the magnetic susceptibility ( , emu mol -1 K -1 ), which is a ratio between the magnetization of the system (M) and the applied magnetic field (H) (equation 9). In magnetic materials, the magnetic susceptibility is inversely proportional to temperature. This inversely linear relationship between the paramagnetic susceptibility and temperature is known as the Curie-Weiss law.

Bleaney-Bowers equation for magnetic susceptibility where is magnetic susceptibility (emu mol -1 K -1 ), M = magnetization (emu), H is applied magnetic field, T is temperature in K, C is the material-specific Curie constant in a unit of cm 3 mol 1 K, N is mass in mol, g is g factor of a free-electron, J is an exchange integration value, k is Boltzmann constant (1.94 × 10 -3 kcal mol -1 ).

In the Curie-susceptibility against temperature (1/ m versus T) intersects at the origin for magnetic materials, as shown in Figure The triplet diradicals have attracted attention due to the presence of their high-spin nature and potential applications in diverse fields such as organic magnetism, MRI (magnetic resonance imaging) contrast agents, and spintronics. In principle, triplet diradical character can be tuned by enlarging ES-T. [53] From a molecular point-of-view, the electronic ground state of polyradical can be predicted using simple Ovchinnikov parity models, where each adjacent spin in the conjugated system is assigned as opposed to its neighbor. [51,[54][55][56][57] According to this model, the simplest molecular model can be illustrated as dimethylethylene. The different isomers can lead to two discrete structures such as trimethylenemethane (TMM) and 1,3-butadiene (Figure 1234567891011121314151617). Diradicaloids are defined by the IUPAC gold book as a diradical liked system. [49] Indeed, it is a sub-class of diradicals that possess a singlet closed-shell ground state. They have attracted attention due to their unique properties through the semi-bonding of the unpaired electrons. These semi-bonding spins have been highlighted as a hybrid resonance between closed and open-shell from, which corresponded to Kekulé structures. [58][59] The first diradicaloid was reported by Chichibabin

11

(Figure 1-18). [60][61] This molecular class adopts a quinoidal structure (11c) in the ground state, having no EPR response at 77 K in solution. However, upon an increment of the temperature, the EPR response rises leading to an observation of the open-shell state (11o).

Figure 1-18

The ground state electronic configuration of the diradicaloid is the singlet diradical as the presence of two degenerate SOMOs. The electronic configuration S1,1 and S2,2 should be less stable than the configuration S1,2 and S due to electron-electron repulsion and vi (Figure 1-14, vide supra). On the other hand, when the two SOMOs are not degenerate and have an interaction with each other, a linear combination between the two SOMOs causes a formation of two new bonding and anti-bonding orbitals. [58,62] Diradicaloid species tend to have ground state closed-shell electronic structure rather than open-shell electronic structure, in which the two electrons are located in the same orbital liked closed-shell molecules. Thus, diradicaloids may refer to all imperfect diradicals, in which the triplet singlet energy gap is small resulting in singlet groundstate preference.

iv. Stable vs persistent radicals

The violation of elementary electronic configuration rules in organic radical leads to stability controversy and is subjective to the user claim. [63] Theoretically, all the radicals are thermodynamically unfavored leading to decomposition at some moment. Griller and Ingold defined if the radical has a longer lifetime than methyl radical in the same measurement conditions. [64] Th isolated, inert to ambient conditions, and storable without any precautions. Thus, the stability of the radical species in this manuscript will be used according to this definition.

v. Enhancing radical stability

Tuning radical stability is decisive for their applications. A compromise between kinetics and thermodynamics plays a crucial role in modulating the lifetime of the radicals. In principle, steric protection is the simplest way to protect the radical from its reactivity. Spin delocalization can also increase the radical stability through two main approaches; 1) extended -conjugated system and 2) directed spin distribution through electron directing group and/or heteroatom. In addition, non-covalent approaches are also introduced and used as an alternative way for benefiting from their dynamic response, and adaptivity of the system. [65] In addition to stabilization via chemical interaction, the electronic configuration of the radical may enhance the radical stability, notably through SOMO-HOMO level inversion (SHI) process. This process may increase radical stability, especially upon light irradiation. [66] Further insight regarding this phenomenon will be described in chapter 2. In practice, several stabilization strategies may be introduced and probably are co-responsible for radical stability.

a) Steric protection

Most organic radicals decompose into several products. The simplest and most effective radical stabilization approach is steric protection. Thanks to this, the radical species can be stabilized or even isolated as a pure compound. For instance, in triphenylmethyl 1, the radical center is protected by the three phenyl rings which have torsion angles of approximately 30 . [67] The stability of this radical can be enhanced by a total or partial chlorination of the three phenyl rings. Two main classes of polychlorinated triphenylmethyl are now renowned as perchlorotriphenylmethyl radical (PTM, 12) and trichlorotriphenylmethyl radical (TTM, 13, Figure 12345678910111213141516171819). [68] They exhibit high stability and tolerance to late-functionalization even in harsh conditions due to their steric protection from polychlorophenyl rings. [42] In the case of TEMPO 9

(vide supra), the radical is stabilized by four methyl groups from the outer sphere which enables this species to be commercialized and storable for several years. Steric protection does not provide only radical stability, but it may bring also chiral elements to the system. Further details regarding the chiral radical system will be discussed in the dedicated section.

b) Spin density modulation

As mentioned above, spin delocalization can be impacted by several main factors in radical systems. First, by extended the -conjugated system, the classic example in this class is phenylenyl 10 (Figure 1-20). [69][70] This radical is stabilized through spin delocalization. The electronic spin distribution of this class of compound is different from PTM and TEMPO by covering the entire system and preventing any dimerization. Extended -conjugation does not always stabilize radical species, since they may lose their stability by molecular twisting. Polar substituents around the system can be introduced for tuning the radical stability. They can be either donating or withdrawing groups. The influence of such substituent tunes the system through inductive and conjugative electronic effects. In radical species, these effects modulate the frontier MO energy levels, which increase their stability. In principle, electron withdrawing groups may prevent the electronic interaction between radicals and molecular oxygen while electron donating groups stabilize the system. Furthermore, radical ions may be stabilized by ion-pairing such as in perylene-3,4:9,10-tetracarboxylic diimide 14. It was mentioned that its stability enhancement comes from the imidazolium group instead of the steric effect (Figure 1-21). [71] All stabilization strategies described above are widely used for carbon-based radicals. [72] There are others classes of organic radicals using heteroatoms such as N, O, and S as a radical center. Heteroatoms-based radicals are usually more stable than carbon-based radicals due to the protection from intermolecular interaction by their lone pair electrons. Furthermore, heteroatoms modulate the spin distribution of SOMOs and modulate the redox properties. [42] There are several examples of heteroatom-based radicals widely known in the literature, especially TEMPO 9 and tetrathiafulvalene (TTF) radical cation 15 [73] , which have high stability and wide use in several applications.

vi. Radicals and materials

Research on stable/persistent organic radicals has attracted attention in both synthetic and materials applications. Thus far, several organic radicals have been investigated, resulting in dynamic, and reactivity information based on EPR spectroscopy. In the past decades, organic radicals have proven their potential in molecular-based magnets, spin labeling, spin trapping [74][75][76] ,

as well as EPR imaging. [77] The development of organic molecular materials with several functionalities are of high potential for replacing inorganic-based materials due to their unique flexibility, robustness, high optical transparency, and easy fabrication. Adding unpaired electrons in the system bring additional opportunities to tune molecular radical systems, additional magnetic properties, and their physicochemical properties for desired applications.

a) Organic magnets Organic radicals have a spin system comparable to inorganic metals. The design of molecular materials has been attempted in the past decades because of the paramagnetic nature of organic radicals where spins are intermolecularly independent from each other. Controlling the spin alignment is possible upon the decrease of temperature where the exchange interaction (J) is comparable to thermal energy in the system. [42] The alignment of the spins is highly important to determine the magnetism of the system. While the Ovchinnikov parity model may be used for 1-D system, the magnetic propagation may occur over all three dimensions in the solid state under the external magnetic field. In this case, bulk magnetic behavior can occur below the critical temperature (Tc). The achievement of bulk organic magnets has been successfully obtained with several radical -nitroxyl nitroxide, verdazyl, and dithiazolyl radicals. Tamura and co-workers established the state-of-the-art in purely organic magnet in p--nitronyl nitroxide 16. [78] The crystal of 16 has ferromagnetic intermolecular interaction below 0.65 K (Figure 1-22). After that, high-spin organic compounds have been extensively developed to form organic magnets with suitable candidates. Achieving high-spin ground-state systems has attracted interest for insight into how the structure-molecular relationship affects the electronic interaction and the macroscopic properties. [42,51,53,[55][56][57] The approach to achieve high-spin molecular systems is based on bridging units that are robust and stable enough for magnetic coupling in sub-unit propagation. In this case, there are several relevant units such as m-phenylene, metallocene, hydrogen bonding, and metal-containing bonds. The representative systems are described in Figure 1-23.

Figure 1-23. High spin ground state molecules with several magnetic coupling units. [79][80][81][82] Beyond the 1D structure, the ferromagnetic property was realized in several systems with the Tc mostly below 2 K. [83] The highest Tc observed in organic radicals was reported by Rawson et al. with sulfur-nitrogen dithiadiazolyl radical 21 (Figure 1-24). The crystal of this radical raises Tc to 36 K. Indeed, the authors could separate two different crystalline structures, which only the -phase exhibiting ferromagnetism while the -phase was antiferromagnetic at the same temperature. Further insights on the crystal packing highlighted the impact of the packing direction on its corresponding magnetism.

b) Spintronics

Tuning the interplay between magnetic and conducting properties is a major issue in materials science. [84] The investigation of a molecular system, which would present both conductivity and magnetism is particularly of interest for the development of spintronics devices. [85][86][87] Indeed, spintronics has attracted interest thanks to the study of molecular spin transportation, which provides several potential applications in magnetic recording systems. In principle, organic radicals provide an insight feature in spin-polarized current, which originates from an unequal spin interaction in the conductivity phase. This spin-preferential is promising for several applications such as spin valves [88][89][90] , spin filters [91] , spin-polarized current detectors [92] , memory devices, and quantum computing systems. [93] As aforementioned, the development of spintronic systems requires a coexistence between conductivity and magnetism in organic materials. Generally, achieving such molecular systems requires planar -donor electron with pendant radical units. [94][95] Moreover, these two units must electronically interact to allow polarization of the spin that created an unusual molecular orbital arrangement so-called SOMO-HOMO inversion (SHI). This SHI electronic configuration allows conductivity to occur in the entire system. [96] More details regarding the SHI phenomenon will be described in the next chapter. Sugano et al. reported the first spin-polarized system with galvinoxyl radical 22. [97][98][99][100] They observed the ferromagnetic intermolecular interaction in galvinoxyl thanks to a combination of spin polarization and charge--donor connected with TEMPO through an imide linkage 23 (Figure 1-25). [101] The charge transfer complexes with acceptor TCNQ and TCNQ-4F were prepared, and the unpaired electrons coupled antiferromagnetically. After that, they prepared several pairing systems, but the conductivity was not observed due to the difficulty in crystal packing. Practically, the conductivity can be achieved in the crystal through the stacked donor units, while the radical unit needs to be stabilized by bulky substituents, which complicates the stacking efficiency. This major issue has been overcome using a diselena-analog of TTF (ESBN) system 24 reported by Sugarawa et al (Figure 1-26). [102][103] The strong magnetic exchange was observed as a great negative magnetoresistance (-70% at 2 K in 9 T). Moreover, a spin-dependent electron transport phenomenon was observed together with strong intramolecular ferromagnetic coupling through magnetic field dependence of magnetization and magnetoresistance experiments. This result proved the presence of interaction between spins and conductivity. Furthermore, they reported an analog of 24 by replacing two hydrogen atoms with bromines (BTBN, 25). [104] The conductivity of the crystal could be controlled in an applied magnetic field by a synergy between conductivity and spins through appropriate molecular designs.

c) Molecular optoelectronics

Open-shell organic molecules with a SOMO energy level provides access to unique photophysical properties such as vis-NIR absorption and emission. [105] These unique properties have demonstrated the potential of such radicals in optoelectronics devices such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), solar cells, and organic photodetectors (OPTs).

Organic light-emitting diodes (OLEDs)

OLEDs have attracted interest as future display panels. However, the photoconversion process in the current generation has some limitations to be overcome. For instance, the firstgeneration OLEDs, so-called fluorescence, have an upper limit of internal quantum efficiency (IQE) of 25% due to a statistical loss of triplet excitons. Although the second generation, phosphorescence, can harvest the triplet excitons and provide maximum IQE, costly materials such as Ir and Pt and possible non-radiative decays resulted in difficulties in practical application. [106] The third generation, thermally activated delayed fluorescence (TADF) overcomes the costly issue of the second generation by using low-cost organic emitters, which allow an interconversion between the singlet and triplet excitons. However, the low emission sharpness and persistent delayed fluorescence time (usually in s-ms range) retain the common problem in this system. [107] Recent studies on open-shell emitters realized a difference in emission mechanism, which is from spin doublet excited state to doublet ground state. [108][109][110] This unique emission process is thermodynamically favored, which can achieve a maximum of 100% IQE by avoiding singlet-triplet spin-statistics. In 2014, Nishihara and co-workers revealed the luminescence properties of PyBTM 26, TTM-based molecules with one pyridinyl substituent, which suggested the potential towards OLEDs application. [111] The first application in OLEDs was realized by Li and co-workers using tris- They also tuned luminescence properties by replacing the carbazole group with several derivatives as well as preparing polymeric forms. However, none of them had better performance in the device. [112][113][114] The breakthrough of OLEDs application was achieved in 2018 with TTM-3NCz,

28. [115] Authors achieved 27% EQE among the highest rank of conventional OLEDs (Figure 1-27).

They further explored the compound in this family, but they could not achieve higher EQE than this system. [66,116] OFETs have limitations in integrated logic circuits. [117] Beyond this limit, the ambipolar OFETs, which have both types of charge conduction, were realized and overcome the unipolar OFET issues.

The challenging development in this field is their stability and reproducibility with balanced holes and electrons mobilities. Organic open-shell molecules are effective hole-transporting molecules with less oxidation potential than closed-shell ones. Nishide and co-workers reported the first nitroxyl radical 29 with hole mobility up to 7.8 × 10 -3 cm 2 V -1 s -1 (Figure 1-28). [118] The importance of organic radicals in the hole-transportation layer was highlighted by Hu and co-workers using dithienothiophene dimer 30. It exhibits better charge conductivity and mobility in its radical form. Besides neutral radical based transistors, diradicaloids have also attracted attention due to their hybrid electronic structure between quinoidal closed-shell and diradical open-shell. Kubo and co-workers reported the first phenylenyl diradicaloid 31 with an ambipolar charge transport system (Figure 1-29). [119] Thin-film experiments showed the charge transport mobility in the range of 10 -3 cm 2 V -1 s -1 . However, the purity of the molecule in the grafting method decreased the OFET performance. The crystalline diradicaloid of 31 was reported by Koike and co-workers by a gasdeposition method. [120] The slipped stacking in the quasi-one-dimensional crystalline phase suggests the crucial role of intermolecular interaction. The ambipolar OFETs from this molecule offered high hole mobility (µh = 7.2 × 10 1 cm 2 •V 1 •s 1 ) comparable to amorphous silicon-based OFETs. Haley and co-workers developed a gram-scale synthesis of a polycyclic hydrocarbon diindeno[b,i]anthracene 32. [121] They highlighted the high stability of the system, which lasts longer than any diradicaloid in this field (t1/2 = 64 days). OFETs fabricated through vapor deposition showed maximum charge transportation in the range of 10 -2 cm 2 V -1 s -1 .

Solar cells

Organic radicals have also attracted interest in solar cell applications due to their high solidstate conductivity and transparency in the visible region. In dye-sensitized solar cells (DSSCs), organic radicals have been highlighted as an alternative redox mediator thanks to their tunable redox potential, higher solubility in water, lower toxicity, and less corrosive ability compared to the common iodine one. [43,122] However, device stability issues have still remained under light harvesting. [123] The most efficient DSSCs with organic radical as a redox couple was reported by Nishide and co-workers with up to 10% efficiency using TEMPO in gel electrolytes. It provided an easier way to fabricate DSSCs with performances close to iodine. [124] Bulk heterojunction solar cells display major efficiency loss due to the recombination of polaron pairs at the donor acceptor domain interfaces. Verdeny et al. have shown that doping active layer with galvinoxyl radical 22 enabled to increase the solar cell efficiency by 18%. [125] They concluded that the spin-flip process by resonant exchange interaction between the spin 1/2 radicals and charged acceptors was effective to convert the polaron pair spin state from singlet to triplet (Figure 1-30). However, this phenomenon requires an energy level matching between closed-shell and open-shell, which is crucial for molecular design.

NIR photothermal materials

NIR photothermal materials have been highlighted in biological applications. The conversion of NIR-light to thermal energy is capable to breach cell tissues. This selective thermal generation in a biologically inactive window has potential in advanced medical therapy and diagnosis. [126] Organic diradicals were highlighted in this application due to the low lying singlet and triplet excited states, providing them with low energy band gaps. Recently, Tang and co-workers reported a stable diradical 33 with high photothermal performance (Figure 1-26). [127] This compound shows high molar absorptivity and low fluorescence quantum yield suggesting a nonradiative decay in this system. Thermal conversion efficiency was calculated to be 72.7% upon 808 nm laser irradiation. Solar-driven water evaporation under sunlight irradiation with molecule 33

showed high thermal efficiency of 87.2% under 1 sun irradiation, demonstrating the promising direction for effective solar energy conversion.

d) Energy storage

Rechargeable batteries are part of our daily life in several portable electronic devices.

Common materials in these items are based on inorganic materials, which show cost as well as toxicity and thermal stability concerns. [128] Similar to optoelectronic applications, the organic radicals provide higher flexibility and robustness compared to the inorganic ones. Recently, organic radicals have attracted attention mainly in redox flow batteries due to their bipolar redox behavior as they can be both oxidized and reduced to facilitate positive and negative half-reactions during the charging/discharging process. [129] Some organic radicals were reported in this application such as nitronyl nitroxide (NNs) [130][131] , or recent emerge helicene carbenium ions. [132] Figure 1-27. Highly stabilized bipolar redox organic radical 34-36.

Chiral organic radicals

Chiral organic compounds offer promising potential towards technological applications.

While chiral closed-shell materials have been intensively investigated, very few studies have paid attention to their chiral radical counterparts due to their potentially low chemical and configurational stability. However, chiral radicals possess spin and chirality in the system, which allows exploring unique properties (NIR-ECD, NIR-CPL, eMCA, MChD, and CISS).

Chirality implemented in organic radicals can be from either chirally perturbed units or through an inherent chiral backbone. A lot of works has reported the generation of chiral radical systems, which could be generated through several approaches, i.e. through either electrochemical, photochemical, or chemical processes. In this section, we are considering only chemically generated and isolated radicals. The molecular chirality is also marked as an important requirement, in which any molecules described in this part would be at least enantiopure under their neutral form.

i. Radicals with lateral chirality

Organic radicals with chiral perturbators are a molecular system that contains two molecular units including chiral closed-shell and achiral open-shell fragments connected via chemical bonding. This connection may be observed between these two through chiroptical characterization.

Most chiral radicals in this class are known as stable radicals, especially nitroxide and tetrathiafuvalene radical cations.

a) Examples of chiral nitroxide radicals

Chiral nitroxide radicals are of particular importance for a wide range of applications such as enantioselective oxidation, stereoselective C-O bond formation, chiral liquid crystals, spin labeling, and anticancer agents. [133] Chiral nitroxide radicals have been extensively studied and reported in several reviews regarding molecular design, enantio-stability, and applications. [46,133] Most of the chiral nitroxide radicals can be classified as a localized radical functionalized by lateral chirality, which is almost exclusively asymmetric carbon (point chirality).

-nitronyl nitroxides. Introducing chiral elements to the system can be performed in two different ways, which are a) introducing the chiral side chain to the C-2 position or b) attaching the chiral elements to the C-4 and/or C-5 of the imidazolyl rings (Figure 1-28 -nitronyl nitroxides 37 [134] and 38 [135] bearing a chirality in the phenyl side for an application in magneto--nitronyl nitroxides 39 with a stereogenic center at the C-4 position of the imidazole ring by aiming an obtaining liquid crystalline compound. [136] Figure 1-28 -nitronyl nitroxides 37-39.

The lateral chiral side chain of nitroxide has been also introduced in pyrrolidinyloxy (PROXYLs) and dimethyloxazolidinyloxy (DOXYLs) radical derivatives. The substituent around the nitroxide radical plays the role of chiral elements in the system such as in molecule 40. The methyl and phenyl group provide C2-symmetric chiral elements into the system (Figure 1-29). [137] Bicyclic PROXYL based radical is also interesting to point out as a conglomerate, which allowed chiral resolution of compound 41 available through recrystallization. [138] In the case of DOXYLs, since the compound could be easily prepared from amino alcohol derivatives, chiral elements in the system could be prepared before forming the radicals. This strategy worked in several chiral precursors such as cholesterol 42 [139] and camphene 43 [140] derivatives. These chiral nitroxide radicals are used in spin-label applications. [133] Figure

b) Examples of tetrathiafuvalene radical cations with lateral chirality

Chiral tetrathiafuvalene (TTF) radical cations are of particular interest in spintronics and molecular conductive materials. Decorating a TTF radical cation with chirality enabled modulating the structural disorder in the conduction path and also furnished a great opportunity to observe magnetochiral effects (vide supra). [30] Meanwhile, chiral TTF-based scaffold has offered opportunities to study the chiroptical response by external stimuli. Similar to chiral nitroxide radicals, chiral TTFs have been profoundly investigated for several decades. The chiral TTF precursors were reviewed by Avarvari and Wallis [141][142][143] and Hasegawa and Iyoda. [START_REF] Hasegawa | Organic Redox Systems[END_REF] The chiral TTF radicals can be classified according to the chiral element attached to the TTF center.

TTF with lateral point chirality:

The first enantiopure TTF derivative, the (S,S,S,S)tetramethyl-BEDT-TTF (44, Figure 1-30), was reported in 1986 by Dunitz and Wallis. [START_REF] Wallis | [END_REF] The ortho-dimethylated analog DM-BEDT-TTF 45 was claimed several years later by Sugawara and co-workers as the (R,R) enantiomer. [146] However, the enantiopure DM-EDT-TTF 46, dimethylated version of EDT-TTF was reported in 2013 by Avarvari, Pop, and co-workers, [147] with chiroptical properties and a theoretical conformational study on the relative stability of the axial or equatorial orientation of the methyl substituents. The metal coordination or charge-transfer complex with compounds 44-46 showed conductivity enhancement and eMCA effect in enantiopure complexes. [30] Beyond the terminal stereogenic center, TTF derivatives with chiral methyl-oxazoline [148- 150] , bis(pyrrole)- [151][152] , and sulfoxides- [153][154] have been also described in Figure 1-31. Moreover, TTF with lateral chiral units can also promote supramolecular self-assembly towards the chiral supramolecular polymers. [155][156][157][158][159][160] TTF radicals with lateral axial chirality: Axial chirality has been firstly introduced in TTF precursors using binaphthyl units by Martin and co-workers (50) in 2000. [161] The connection between the TTF and binaphthyl can be realized as flexible compounds as reported by Martin or rigid compounds 51 as reported by Fourmigué et al. (Figure 1-32). [162][163][164] These compounds displayed a modification of their chiroptical properties by varying the dihedral angle and also the electrochemical recognition. In addition to binaphthyl moiety, Hasegawa et al. introduced the allene platform with TTF units to obtain electroactive axially chiral TTF compounds, for instance, compound 52, which showed strong redox modulation of the ECD signal. [165][166] TTF radicals with lateral planar chirality: Planar chirality has been firstly reported as TTFparacyclophane derivatives by Hasegawa et al. as bis(TTF)-paracyclophanes 53 (Figure 1-33). [167] Compound 53 showing redox modulation of the ECD signal which can be used as a chiral dopant in liquid crystals. More recently, Avarvari et al. reported a single crystal of mono-TTFparacyclophanes derivatives with correlated experimental chiroptical properties with theoretical TD-DFT calculations for absolute configurations. [168]

ii. Inherently chiral radicals

An inherently chiral radical is a molecular system where radical locates within a chiral backbone. Several chiral systems have been reported especially helicene thanks to such high chiroptical response and stability due to delocalization entire the backbone. Helicenic radicals have been reviewed by Tani and co-workers. [169] However, there are some other inherent chiral radicals reported in the literature. In this part, we will highlight all the molecular systems described in the literature by their type of chirality with their chiroptical response, radical stability, and enantiomeric stability if concerned.

a) Chiral organic radical with propeller chirality

Chiral radicals with propeller chirality were solely reported with triarylmethyl derivatives (TAM), which are chiral once there is any substituent in the ortho position. The first chiral radical with triaryl derivatives were reported by Veciana and co-workers, who have mainly focused on TTM and PTM moieties. The first chiral triphenylmethyl radical was obtained in form of polyradical with multiple PTM groups, compound 55-56 (Figure 1-34a). [170] These compound series are ferromagnetic species, stable and tolerant to high temperature (stable for more than 1 h in the air as C2-56 and D3-56 and characterized by chiral HPLC and difference in EPR spectra due to a small chiroptical response.

Soon after, compound 57 was reported their synthesis and crystal structure showing the influence of chirality in torsion angle and EPR spectra (Figure 1-34b and 1-34c). [171] In 1995, the first chiral PTM monoradical (+)-12 was obtained in enantiopure form by chiral HPLC separation. [172] A low racemization barrier ( = 23.6 kcal mol -1 ) was obtained.

ECD response of this compou -1 cm -1 at 330 nm with associate bisignate signals with much lower intensities at 280, 330, 395, 430, and 480 nm.

Furthermore, The authors studied chiroptical properties of (+)-12 in comparison with TTM radical (+)-13 in frozen CCl4. [173] They found that there were two maxima ECD responses instead of one -24 and -60 M -1 cm -1 , respectively) while (+)-13 has slightly redshifted More recently, Veciana et al. studied another series of chiral TTM radicals by replacing the chlorine with bromine atoms 58. [174] The compound showed a higher racemization barrier with no still relatively low due to their low rotational power. This compound showed slightly redshift and equal to 1.6 × 10 -3 at 380 nm, which is in agreement with 13. In line with ECD, the CPL response was similar to 13 with the same range of value (7 × 10 -4 at 593 nm).

Another chiral radical with propeller chirality was reported by Liu, Hou et al. with a tetrathiatriarylmethyl 59. [175] This molecule has two chiral hydroxy groups connecting through a methylene bridge between two thiols in a single TAM unit. With this strategy, they could separate four enantiomers with three chiral centers. This compound is persistent with high enantiomeric provided 8 signals, which are positive at 209, 236, 278, 359, and 445 nm and negative at 263, 317, and 404 nm. However, the signal intensities are relatively low. EPR investigation provided quartet signal in (1:3:3:1) ratio suggesting the interaction between the radical and three identical arylprotons.

Chiral radicals with propeller chirality have been investigated over decades. Although this type of radical is known to be highly persistent, all these compounds display low racemization barriers from the rotation of the phenyl rings. Therefore, the next section will consist of persistent radicals with higher enantiomeric stability.

b) Chiral organic radical with helical chirality

The first helically chiral monoradical was reported by Chang, Weissman, and Allendoerfer who studied kinetic electron exchange study of carbo [6]helicene (60) anion radical by reduction with potassium metal and later with EPR, ENDOR, and optical rotation studies. [176][177][178] EPR and ENDOR exhibited 10 hyperfine constants, which are higher than calculation. They claimed that the additional hyperfine coupling may result from asymmetric interaction with the counter cation.

Furthermore, beyond the monoradical, they also investigated diradical and triradical species, with the former one being EPR silent thanks to its diamagnetic property. ORD of the three radical species was also examined, thus probing the difference in the signature of optical activity between the three radicals. Importantly, K + 60 -has a further ORD signature with a peak at 545 nm proving the radical nature of the compound. These three species were remeasured by Fey and co-workers using ENDOR and TRIPLE techniques, which are measurements of spin-coupling with neighbor nuclei. [179][START_REF] Dorio | Multiple Electron Resonance Spectroscopy[END_REF] With this technique, they could obtain 8 hyperfine constants, which is in line with the calculation. Based on these reports, unpaired spins of carbo [6]helicene radicals are fully delocalized over the entire backbone. Tanaka and co-workers reported the preparation of thiahetero [7]helicene 61 and its anion radical using Na. [START_REF] Tanaka | [END_REF] EPR signature was assigned to 5 sets of protons, which were in line with the theoretical aspect. However, there was no clear interaction between the two terminal thiophenes and regardless of molecular configuration.

Chiral nitroxide radicals marked their importance in several applications. Among them, compound 62 was prepared by Rychnovsky et al., which is one chiral nitroxide-based radical with helical chirality (Figure 1-36). This compound was used in the enantioselective oxidation of secondary alcohol as a catalyst with a maximum of 98 % ee. [182] The result highlighted the efficiency of nonenzymatic catalysts for such kind of reaction.

Although the examples described above are chiral compounds, there were few chiroptical properties reported. Rajca et al. first reported in 2010 chiroptical properties of a helical chiral radical, namely thia [7]helicene 63 (Figure 1-37). [183] This molecule is the first chiral radical which is configurationally stable at room temperature. The ECD of the molecule exhibited an overlap with max = 287 nm and new bisignate signals at 360 and 510 highlighting its configurational stability. They claimed that ECD observation confirms that there is no planar structure of quasi- [8]-circulene type nor epimers formation at low temperature, which can diminish ECD signals. However, this persistent radical has a half-life of 20 minutes at room temperature. In 2012, Morita et al. reported the first chiral neutral radical with diazaphenalenyl- [4]helicene 64 (Figure 1-38). [184] This compound is chemically and configurationally stable at room temperature. EPR showed a well-resolved hyperfine structure as well as ENDOR/TRIPLE measurement. This suggested that the unpaired electron is delocalized over the entire molecule, which is in agreement with the small SOMO-LUMO energy gap obtained from theoretical calculation. ECD showed an intense signal with Cotton effect over UV-visible region at 308, 362, 460, 547 nm. In terms of stability, 64 is stable for a few weeks in a solid state while it is stable for a few days in solution. Degradation of this compound suggests air-oxidized derivatives as a major product. [184][185][186] b) ECD spectra and chiroptical switching in acetonitrile. Spectra of (P)-and (M)-66 -were generated electrochemically in an OTTLE cell. Reversible electrochemical switching for several cycles is shown for the M enantiomer at two different wavelengths (Top). Our group has contributed to this field with two examples of chiral radical species. The first one is the radical cationic species of ethylenedithio-tetrathiafulvalene [6]helicenes 65. [185] The molecule has an unprecedented topology with an intramolecular charge transfer band at 436 nm. Formation of the 65 using NOSbF6 as an oxidant diminished an ICT band while created a new NIR band centered at 950 nm. The structure also preserved chiroptical properties by several chemically cycling oxidized-reduced processes. This molecular structure shows a potentiality for the preparation of crystalline helical conducting materials thanks to the synergy between TTF and helicene.

Another carbo [6]helicene-based compound was reported as an ortho-quinone derivative 66. [186] This compound is stable as radical anionic species by reduction with lithium metal and confirmed a formation of Li + (THF)266 -by EPR, ENDOR, and TRIPLE, which the latter provided more insight regarding ion-pair contribution. Furthermore, this compound is also configurationally stable as observed by the reversible switch in spectroelectrochemical ECD measurement, in which the UV region was globally red-shift and broaden together with a new visible band at 625 nm (Figure 1-38b). Furthermore, thanks to the formation of the Li complex upon the chemical reduction process, this compound is highly sensitive to the change of chelating agent.

Diastereomeric chiral recognition was attempted using BINAPO, which revealed different hyperfine coupling in ENDOR spectroscopy. Double helicene was also attracted attention, Seki et al. reported a synthesis of double hetero [4]helicene 67 from phenothiazine building block (Figure 1-39). [187] This chiral compound is enantioseparable because of molecular bending. Radical observation using spectroelectrochemical exhibited new absorption bands at 545 and 1500 nm. Furthermore, 67 was isolated as racemate with tris(4-(4-BrPh)3NSbCl6)

showing that planarity of 67 is more than its corresponding neutral state. This planarity also confirmed EPR as observed 5 hyperfine splittings (Figure 1-39b). 67 is also highly persistent for more than 2 weeks under ambient atmosphere. However, 67 promptly racemized due to their low racemization barrier ( = 26.9 kcal mol -1 ), leading to a lack of chiroptical response at the radical state. Polyaromatic hydrocarbons (PAHs) are of interesting systems due to their close relationship to nanographene. Naphto[3,2,1-no]tetraphene 68 was reported as the first fully PAH chiral neutral radical. [188] Spin density of 68 distributed over the entire core without any uniform pattern. This compound is persistent as its fully protected, and its monoradical behavior follows Curie-Weiss law as observed by EPR. UV spectrum of 68 showed maximum absorption at 537 nm, which corresponds to SOMO-LUMO transition. However, as its chiral backbone is a carbo [5]helicene, the racemization barrier of the radical is too small ( = 26.9 kcal mol -1 ) to record ECD spectra of each enantiomer.

Rajca et al. reported an analog of 63 by replacing a central thiophene group with a pyrrole group and studied as 69. [189] The nitrogen substitution enables to generate radical cation and neutral radical species by addition of a weak base such as Cs2CO3 (Figure 1-39d). The neutral species could be prepared from anionic species as well (pre-deprotonation by either LDA or NaH). This species is persistent and has a half-life of 8 h under inert atmosphere. The neutral radical 69 showed less stability than 69 as well as less delocalization effect as less hyperfine coupling was observed in EPR. Interestingly, theoretical calculations suggested that SOMO-HOMO inversion (SHI) occurred regardless of the solvent. Although the attempt to get diradical species was not successful, theoretical calculation suggests that the diradical species possesses triplet ground state with relatively low singlet-triplet transition ( 2 kcal mol -1 ).

Hetero [4]helicenes are highly interesting due to their facile synthetic approach and possibility towards spintronic applications. Kivala et al. reported their findings on dithia-bridged hetero [4]helicene 70, which was fully protected at all reactive para positions (Figure 1-40). [190] Crystal structure of monoradical 70 SbF6 -showed more planarity of the system than the neutral one. The EPR spectrum of 70 showed a signal centered at g 2.00, within the range of nitrogen centered organic radicals. UV-vis spectra of 70 exhibited maximum absorption at 564 nm with a broad NIR signal centered at 1270 nm. Moreover, ECD spectra showed Cotton effects up to 1500 nm, which was confirmed by VCD experiment. Osuka et al. reported an alternative stabilization route using porphyrin fused to helicene backbone. [191] With this approach, they succeeded to obtain air stable chiral radicals 71 and 72 in their neutral forms. UV-vis spectroscopy of these molecules exhibited weak Soret and Q-band patterns between 490-600 nm linked with broad absorption from 650-1650 nm. Furthermore, these radicals have strong ECD signals thanks to cooperation between helicenic structures and porphyrin.

The ECD spectra exhibited Cotton effects up to 1400 nm with a high gabs value at Soret-like band showing the desymmetrized porphyrin by the helicene segment. The radical character was confirmed by EPR and SQUID, which the latter showing a Curie constant following monoradical behavior.

Tani et al. reported a synthesis of azulenylhelicene 73 from two trimethylazulenes fused with an isobenzothiophene. [192] They succeeded to prepare and crystallize an air persistent monoradical 73 using AgPF6 as an oxidant. As above, the crystal structure showed more planarity -delocalization and reduce the distance between the two azulenes, which was confirmed by EPR and DFT calculation. UV-vis spectrum exhibited a new absorption band at 600 nm and a broad NIR band around 1500 nm, which are in agreement with a new mirrorimage signal observed in ECD up to 700 nm. Although the crystal structure was obtained, which claimed that the 73 is stable in air, there was no time-dependent measurement to estimate its lifetime.

Recently, double oxa [7]helicene 74 was reported by Peng, Hu et al. from a fusion between benzofuran and terphenyl core. [193] Chemical oxidation of 74 using AgBF4 exhibited two sharp absorption bands at 425 and 685 nm and a broad NIR absorption in the range of 770-1200 nm. The radical species could be chemically reduced using SnCl2. Further exploration on doubly oxidized species was carried out using the spectroelectrochemistry technique, in which the NIR absorption showed more structure while the EPR signal disappeared. This observation suggests that the doubly oxidized species is diradicaloid. Nevertheless, the authors did not describe any chiroptical properties of the oxidized species.

c) Chiral organic radical with inherent chirality

Polyacenes are interesting PAH derivatives since their most stable conformation is not planar. [194] Due to this twisted structure, twistacenes have emerged as a potential chiral radical candidate. Although in many crystal structures of polyacenes, twisted conformations are the most stable ones, it remains difficult to obtain a chiroptical response from these radical species due to their low racemization barrier. Rathore et al. proposed the first enantiopure radical twistacene derivative 75 (Figure 1-41, left). [195] This radical species is stable, and X-ray crystallography showed a small change in the twist angle ( -vis titration exhibited a broad vis-NIR signal between 500-900 nm. However, as mentioned above, there was no chiroptical properties investigation due to the low racemization barrier (t1/2 1 h at room temperature). Interestingly, the authors attempted to calculate derivative 76, which was equipped with some steric hindrance around the structure. The result highlighted the possibility to improve enantiomeric stability, with a much higher racemization barrier than 76 for compounds 78 and 79.

The steric hindrance approach was confirmed by Gidron et al. by synthesizing twistacene derivatives 80-83 with a diagonally locked chain (Cn) to overcome conformational flip issues. [196] Oxidized species showed a change from pale yellow to bright green solution with three new transitions at 500, 600-750, and 1000-1800 nm (Figure 1-41, right). As expected, enantiopure radicals showed Cotton effects related to these three new transitions in all derivatives with different lengths of the locked chain (Cn). As observed in UV, EPR showed three weak hyperfine couplings resulting from spin delocalization in the central ring, but there is no effect from the hydrocarbon chain. iii.

Chiral radicals with more than one spin

Polyradicals are of interest due to insights regarding their interaction between spin and molecular structure. The presence of chirality in polyradicals may provide enhanced spin-filtering properties for the development of the next generation of spintronics. The design of intrinsically chiral diradical is extremely difficult for controlling spin states as well as enantiomeric stability.

Thus, the number of intrinsic polyradicals is limited to few examples.

a) Chiral diradicals

The chirality influence on the diradical species was described by Liu et al. by using tritylnitroxide system. [197] Compound 84 was synthesized by using L-proline linked between two radical units. The compound has three chiral centers, and can be separated as two pairs of diastereomers consisting of two enantiomers for each pair. The ECD spectrum of 84 depicted characteristics of the trityl radical with two strong positive Cotton effects at 384 nm and 467 nm and two relatively weak negative Cotton effects at 324 and 352 nm. These characteristic peaks are mirror-images for both diastereomers due to the small contribution from the nitroxide part, which is negligible. They studied further the chiral induced electron exchange interaction (J) between the two spins in both solution and solid state leading to differences in dinuclear polarization (DNP) effects. The result suggests the crucial role of the chirality nearby nitroxide, which governed the drastic difference in the DNP effect.

The first intrinsic chiral diradical was isolated by Teki et al. in 2018 using azaacene doublefused forming hash-mark-shape molecule 85 (Figure 1-42). [198] This molecule can carry up to 2 spins as depicted by the first two reversible waves in electrochemistry. However, there is no spin interaction observed due to the distance between the two spins. UV-vis-NIR of diradical species exhibited two new absorption bands between 450-700 and 700-1100 nm, which suggest a lower energy transition of the SOMO-LUMO level. ECD of 85 also showed bisignate signal; a negative one at about 625 nm (for the (Ra)-85 -10 M -1 cm -1 ) and a positive one between 700-1100 nm (for the (Ra)-85 max +2.5 M -1 cm -1 ) suggesting that this diradical species is configurationally stable (Figure 1-42b).

Rajca et al. reported bisdiaza [5]helicene 86 as the first persistent chiral triplet ground state diradical. [199] Cyclic voltammogram of this compound showed two reversible waves at 0.39 and 0.99

V vs. SCE. Corresponding mono-and diradical could be prepared by a different approach. Sequential oxidation by the addition of 1 equivalent of [Th] + BF4 -offered the corresponding mono and diradical species. The monoradical showed maximum absorptions at 322, 358, and 744-880 nm. Upon the addition of the second equivalent of the oxidant, new bands were observed at 553, 651, and 899 nm.

The chiroptical response of the diradical species suggested that the molecule has a strong response ( = 7 × 10 -3 at 385 nm) and is configurationally stable even with an excess of oxidant for longer than 48 hours. Furthermore, EPR mea s = 2) suggesting triplet diradical behavior. Magnetic susceptibility measurement suggested the diradical 86 has triplet ground state with an estimated singlet-S-T = 0.3 kcal mol -1 , Figure 1-42c).

b) Chiral diradicaloids

Chiroptical properties of diradicaloids can be strongly changed during an interconversion between closed-shell and open-shell states, offering their potentials towards chiroptical switches. [20,58] et al. [188] They described a synthesis of 87, which is the only chiral isomer of heptazethrene so-called cethrene (Figure 1-43). This molecule was not stable under air and lead to the planarized product 87a. The stability was enhanced to 5 hours under argon, which allowed to detect it by NMR, UV-vis, and EPR. EPR measurement gave a hyperfine splitting, which could not be attributed due to several unequal S-T calculated from the VT-EPR experiment was found to be equal to 5.6 kcal•mol -1 . Although ECD could not be obtained from radical species due to signal-to-noise ratio, the authors suggested that the radical is configurationally stable because of the high racemization barrier of the precursor. Soon after, the stability of the cethrene radical had been increased by the addition of methyl substituents in ortho-position to the helicene core as dimethylcethrene 88. [200] This addition directly S-T value, which dramatically increased to 10 kcal•mol -1 thanks to some longer distance between fjord carbons and FMOs overlapping and also confirmed by EPR silence at room temperature. Due to the high stability of this system, UV irradiation could break the link between the two fjords carbon then the system could be reversed to the thermal product, which is in an accordance with Woodward-Hoffmann rules. ECD spectra of this system clearly displayed the difference between o-88 and c-88a, with the disappearance of the broad signal at 650 nm and the formation of a sharp signal at 415 nm. Moreover, this system showed photoswitching properties using different irradiation energies, which may result in a novel all-organic chiral magnetic switch operated by light irradiation.

Lastly, a series of novel helicene 5,14-diaryldiindeno[2,1-f:1 ,2 -j]picenes 89a-c, which contain a [7]helicene backbone, was synthesized and rationalized by Hsieh et al. (Figure 1-44). [201] The diradicaloids were isolated and their crystal structures showing the length between two fjords falling between [6]-and [7] helicene. The magnetic properties showed thermal dependency, which enabled to determine singlet-triplet gap in the range of 4.2-5.1 kcal•mol -1 . UV-vis spectroscopy showed absorption at max = 750-790 nm, which highlighted the effect of electronic properties on the twisting angle. The configurational stability was high enough to experimentally measure and provide high 500 M -1 cm -1 ). Furthermore, thanks to this exceptional diradical character and configurational stability, this series was employed in OFET and incorporated in perovskite solar cells. [202] In brief, chiral radicals provide unique properties and interactions between chirality and spins. Although intrinsically chiral radicals have been studied over a long period, isolation of such persistent radicals remained challenging, with only a few examples in the last decade. In terms of chiroptical properties, the helical systems can provide strong ECD responses, as expected by the rotational power of the system in comparison to other types of chirality. However, in terms of luminescence, only recently the propeller chirality exhibited this property in the case of triarylmethyl systems. Chiral radicals with more than a single spin are even more rare, challenging to obtain, and limited to only a few systems. This reinforces the motivation to further investigate other chiral radical systems, which will be presented in the rest of this manuscript.

Chapter 2

Axial and Helical Chiral Bicarbazole Systems: A New Family of Stable Chiral Mono-and Diradical Cations Chapter 2: Axial and helical chiral bicarbazole systems: A new family of stable chiral mono-and diradical cations 2.1 Summary

In the previous chapter, we presented some basic concepts about chirality, radicals, and selected examples of organic chiral radicals. These compounds showed a promising potential towards magnetic, spintronic, and optoelectronic applications. While most of the organic radicals have a classical electronic configuration, i.e. where the SOMO is the highest occupied orbital, [1][2] some of them do not follow this general rule, leading to an uncommon electronic configuration, namely SOMO-HOMO inversion (SHI). In this chapter, we firstly review this particular family of radicals with some theoretical and experimental insights regarding the SHI electronic configuration and selected examples of organic radicals displaying SHI.

Following this bibliographic part, we turn our attention to the synthesis of C2-symmetric bicarbazole systems, namely BICOL derivatives, an analog of BINOL, and the investigation of their unexplored electronic and chiroptical properties. Our first approach has consisted in the functionalization of both the nitrogen and oxygen positions to afford 128 and 129, presenting two different types of chirality, namely axial vs. helical (vide infra). These two molecules show a difference in photophysical and chiroptical properties in solution as well as their electrochemical activities. This notably allows us to investigate the formation of novel persistent chiral organic monoradical cations based on bicarbazole molecular design with an unprecedented stability dependence on the chirality element. Indeed, a high persistence is observed in unprotected axial bicarbazole radicals in comparison with the helical bicarbazole radicals and a monocarbazole radical model. These results were experimentally and theoretically rationalized, revealing the SHI formation in both axial and helical bicarbazole monoradicals, along with a subtle difference of electronic coupling between the two carbazole units. These two aspects can be directly related to the relative dihedral angle between the two carbazole systems, which can explain the unprecedented stability of the axial monoradical. Such findings allowed us to explore in-depth the SHI in chiral organic radical systems and provide new insights regarding its impact on the stability of organic radicals. Finally, these specific electronic properties allowed us to prepare an intrinsically chiral diradical, which notably displayed near-infrared electronic circular dichroism responses up to 1100 nm and almost degenerate singlet-triplet ground states with weak antiferromagnetic interactions evaluated by superconducting quantum interference device (SQUID) experiments. [3]

SOMO-HOMO inversion: Basic considerations and examples i. General aspects

Basic electronic configuration principles exclusion, determine the most stable electronic ground state of atoms and molecules. [4][5][6] The electronic configuration of radical compounds usually follows these basic principles where the SOMO (singly occupied molecular orbital) is energetically higher than any doubly occupied orbitals.

However, several metal complexes [7][8][9] , carbenes [4,10] , and organic radicals do not follow this rule, and present a unique molecular orbital arrangement where the SOMO lies below the highest occupied molecular orbitals (HOMO(s)) qualified as SOMO-HOMO inversion (SHI, Figure 2-1).

This unusual electronic configuration sets the electronic properties of these radicals apart from the common situation where the SOMO is the highest occupied molecular orbital of the system. For instance, further ionization of radical with SHI will result in the formation of an open-shell diradical, instead of a closed-shell configuration, resulting from the removal of one electron from the HOMO level. The SHI electronic configuration has been under debate in both theoretical and experimental aspects. Some SHI radicals have been associated with an unprecedented stabilization of radicals and proved their potential in several applications such as spin-polarized donors for conductive materials [11] and luminescence emitters for OLED applications with higher photostability. [12] Besides the material applications, organic radicals with SHI have been presented as a key intermediate for the regiospecific reaction of C(sp 3 )H-amination and photocatalytic allylation, providing an alternative direction for organic synthesis. [13][14] In this section, we propose to review some basic considerations of SHI and common experimental evidences of such electronic configuration with selected examples of organic radicals with SHI configuration.

ii. Basic considerations SHI configuration may be viewed as a non-Aufbau electronic configuration. Indeed, this electronic configuration is often associated with a violation of the Aufbau principle, which has been observed in metal complexes and noted for certain types of high-spin restricted open-shell Hartree-Fock (ROHF) calculations. [15] However, -spin orbital is higher than the one of the highest occupied -spin orbital (Figure 2-1). [16] To have a clear picture of this aspect, it is important to perform spin-unrestricted MO calculations (either spin-unrestricted Hartree-Fock or Kohn-Sham (KS) density functional theory) to realize and match pairs of spin ( ) and spin ( ), which may be energetically different. This has been recently investigated by our theoretical collaborators, which have identified fundamental insights on why the energy of the SOMO in some radicals is below the HOMO energy. [5] They notably found that the formation of SHI radicals from closed-shell parents is likely to occur when the two electrons in the HOMO level of the neutral parent are stronger in repelling each other than the repulsion between the HOMO and other frontier molecular orbitals (FMOs). In the next pages, we describe selected examples of open-shell molecular systems displaying SHI, as well as the experimental and theoretical evidences that completely characterize this unusual electronic configuration. After that, we tentatively highlight some key molecular designs that may be followed to obtain organic radicals with SHI and illustrate these aspects with our experimental and theoretical results on bicarbazole systems.

iii. Selected examples of organic open-shell systems with SHI

While the term SHI has been popularized in the last decades, SHI electronic configuration has been already observed in radical systems for 30 years with notably the work of Kinoshita et al.

on the galvinoxyl radical 22. [17] The authors reported the evidence of intermolecular ferromagnetic interactions in galvinoxyl crystal, together with spin-unrestricted calculations of the electronic configuration of the galvinoxyl radical. In the latter, a clear spin-polarization occurs and the -spin orbital energy is lower than the one of -spin, with notably a SOMO lower in energy than the HOMO, suggesting that the oxidation of radical with such electronic configuration may lead to the formation of triplet diradical (Figure 2-2). [18][19][20] This pioneering work has been followed by Sugimoto [21] , Sawaki [22] , and Sugawara [23][24][25][26][27] in the 90s on spin-polarized donors. Indeed, Sugawara and co-workers developed several molecular systems combining an electroactive donor molecule and a pendant radical named spin-polarized donors (see explanation below) and resulting in several examples with SHI. Such compound family has been designed for introducing a new building block in organic spintronic applications, where both magnetic and spin conductivity are co-existed (Figure 23).

The general design of these compounds is based on stable radical units such as the nitronyl nitroxide, functionalized by a neutral organic electron donor fragment in a way that the SOMO of the radical and the HOMO of donor fragments can be considered as spatially disjoint. This can be realized by a torsion angle between the two fragments, affording a weak orbital overlap of these two fragments (Figure 2-4a). The SHI in these molecules could be tuned by the interplay between the -SOMO energy level and donor strength of the second electroactive center, which provides three possible scenarios in the systems, as illustrated with the examples depicted in Figure 2-4b and 2-4c. [28] Figure (A) When a weak donor is connected to the radical, for instance, phenyl nitronyl nitroxide 91l -SOMO is higher in energy than the HOMOs. The spin-polarization, in this case, is not strong enough to place the HOMO to be higher in energy -SOMO, resulting in a common open-shell molecular orbital arrangement with SOMO being the highest occupied orbital in energy.

(B) In the case of dimethylamino nitronyl nitroxide 91c -SOMO is higher in energy than -HOMO, -HOMO due to the donor strength and spin-polarization.

Moreover, the energetic splitting between the -HOMO and -HOMO could come from the difference in coulombic repulsion in the spin-unrestricted calculation. Thus, this electronic configuration affords what we call here a partial SHI, where the oxidation process prefers occurring at the --SOMO.

(C) Increasing the donor strength character of the organic donor unit results in a complete SHI electronic configuration, where both -and -HOMO energy levels become higher in energy -SOMO. For instance, p-aminophenyl nitronyl nitroxide 91m displays such electronic configuration and formation of the corresponding diradical compounds by chemical oxidation, which afford a diradical with triplet ground-state multiplicit While for the moment we have discussed the SHI in terms of schematic illustrations of orbitals, it seems important to note here that the work of Sugawara and his collaborators brings, in addition to theoretical experiments, experimental evidence of SHI, as well as molecular design rules to obtain organic spin-polarized donors. They introduced, for instance, the importance to have limited electronic interaction between the radical center and the electron donor unit, to afford a high-spin diradical system upon oxidation of the HOMO level, following the work of Borden and

Davidson and the notion of disjoint SOMOs (Figure 2345). [29][30][31] Indeed, the generation of diradical triplet ground state from a spin-polarized donor compound has been seen as an indirect indication of SHI, together with a lower oxidation potential of the donor unit than the one recorded for the oxidation of the radical center, and an on-site coulombic repulsion of SOMO larger than the orbital energy difference between the HOMO and the SOMO. [28] Sugawara et al. applied these general rules to construct a variety of spin-polarized donors including mainly nitronil nitroxide as the radical unit, functionalized by different donors fragments based on amino groups, pyrrole, [32][33][34][35][36] and other tetrathiafulvalene derivatives (Figure 23456). [37][38][39][40][41][42][43][44][45] and2-7c). [46] The observed SHI is present only for the complex since the corresponding free-ligand 92a shows a usual electronic configuration of radical. SHI for the complex was thus attributed to an antibonding interaction of the HOMO of TEMPOdt and HOMO of Pt(tBubpy) 2+ . By this approach, the SHI in radical-metal complexes was realized with several metallic ions such as nickel(II), gold(III), and palladium(II), Figure 2345678. [47][48][49]

c) SHI in ion-radical system

The first investigation on the impact of SHI on the stability of radicals was reported by Coote et al. [50][51] The authors used a functionalized TEMPO with a carboxylic pendent 95 (Figure In a complementary manner to this distonic radical anion, the first example of the radical cation with SHI was realized by Rajca et al. with the in azathia [7]helicene 75. [52] The radical cation of 75 has a relatively small difference between its two oxidation processes ca. 0.2 V lower than the one of the parent thia [7]helicene 69 (ca. 0.5 V), indicating a small energy gap between the HOMO and HOMO-1 levels. By comparison with truncated model compound 75a and with previous thia [7]helicene 69 and oxathia [7]helicene 97, the authors showed that only 75 adopts the SHI electronic configuration (Figure 2-10). Our collaborator recently revisited this compound and confirmed the presence of SHI by calculations (Figure 234567891011). [5] They rationalized such electronic configuration by the nearly degenerated HOMO and HOMO-1 of 75 and the strong self-coulombic electronic repulsion in the former, ultimately affording SHI upon radical formation. Following these studies, the interest in organic radicals showing SHI has attracted significant interest for fundamental and applied reasons. Given the abundance of distonic radical ions and electroactive ion radicals, the scope of organic radical system with SHI has been enlarged

to several derivatives such as TTF, [53][54] , DNA, [55][56] amino acid, [57][58][59] (3,5-dichloro-4pyridyl)bis(2,4,6-trichlorophenyl)methyl (PyBTM) radical, [60] azulenes and biazulenes, [61] and spiroconjugated compounds (Figure 23456789101112). [62] Figure ). [63] The SHI was only obtained in the radical cation 107 , which is different comparing to thia [7]helicene 69. The oxidized species 106

and 107 showed a persistent character at 193 K (half-life value suggested for over 24 hours).

However, at room temperature, 107 showed much less stability (t1/2 < 5 minutes vs. 2 hours for 106 ) contrary to the other SHI species. The authors suggested that the steric hindrance plays a decisive role in stabilizing the investigated corresponding radical cation.

d) Application of SHI radicals in OLEDs

Generally, the application of organic radicals with SHI has been mainly related to the magnetic and spin properties of the system. The recent study of Li, Bredas, and Friend provides further innovative direction of organic radicals with SHI in OLED applications. [12] As mentioned in chapter 1 (see page 25), the luminescence of radicals can provide a maximum internal quantum efficiency of 100% due to the doublet emission pathway. [64][65] However, the development of luminescent radicals remains challenging because of the poorly understood photophysical of radical excited states, and the often poor photostability under UV irradiation. Thus far, the main molecular design for luminescent radicals is based on donor-radical systems with luminescent polychlorotriphenylmethyl radical units such as perchlorotriphenylmethyl (PTM) or trichlorotriphenylmethyl (TTM) radical and nitrogen derivatives as donor moieties. [12,60,[66][67] This design is similar to the spin-polarized donor systems, and eventually can display SHI depending on the electronic interaction between neutral donor and radical fragments. [68] ). [12] In comparison to their hydrogenated precursors (108-H and 109-H), the oxidation processes remain at the same value, confirming the oxidation of donor fragments. In addition, the CV profiles also exhibited a reduction peak corresponding to the reduction of the PTM radicals. In contrast, the oxidation potential of 28 is found at smaller values than those measured for both radical and donor fragments, indicating a higher hybridization between these two units (Figure 2-16, middle). As a result, a non-SHI electronic configuration is obtained in this molecule. The crucial impact of SHI electronic configuration in these species is the photostability upon UV-irradiation. In comparison to the PTM radical fragment, 14, compound 108 displays a half-life photostability up to 100,000 folds higher in value. Furthermore, the SHI also provided higher photoluminescence quantum yield (PLQY, up to 54%) thanks to a significant kinetic reduction of the excited-state non-radiative pathway. This result highlights a promising opportunity to design a new generation of efficient emitters for OLED devices.

e) Perspectives and introduction of my work on organic chiral radical with SHI

This part has focused on the basic aspects of the SOMO-HOMO inversion (SHI) where the SOMO, the unpaired molecular orbital associated with the radical character of the system, lies energetically below one or several doubly occupied molecular orbitals. Besides computational rationalization, some associated experiments can determine the SHI configuration, such as electrochemistry and the formation of the corresponding polyradical species upon oxidation of the SHI radical. SHI in organic radicals has been observed for several decades in a wide range of compounds such as spin-polarized donors, organometallic complexes, and distorted ion radicals.

However, understanding and rationalizing its consequences on the molecular properties/reactivity remains poorly understood since there are no general criteria to control the electronic interaction between frontier molecular orbitals from one molecular class to another. Thus far, according to the examples described above, an open-shell molecular system may possess SHI configuration if presenting the following conditions;

1. The presence of at least two electroactive centers, which can be spin centers upon either oxidation or reduction process.

2. The radical center and the fragment bearing the HOMO level should present spatially disjoint orbitals, following the meaning used by Borden-Davidson. [29] 3. The second electroactive center should have strong electronic/coulombic interaction in FMOs to increase the HOMO energy level and be higher than SOMO.

In addition, as mentioned in chapter 1, SHI has emerged as a novel factor that can contribute to the chemical stabilization of a radical molecule, in a complementary manner than the use of bulky substituents and the radical delocalization over the -conjugated molecular backbone.

With this in mind, we wondered if the electronic and magnetic features of an organic SHI radical could be combined with the axial chirality, and what would the impact on the chemical and configurational stability of the latter, since these issues are often currently hampering the field of research on molecular chiral open-shell systems. [69] In this regard, we have turned our attention to the C2-bicarbazole system, an analog of BINOL named BICOL. We firstly revisited the synthesis of such compounds and some derivatives to thoroughly characterize their photophysical and chiroptical properties, both experimentally and theoretically, with a focus on the impact of the torsion angle between the two carbazole systems.

We then investigated the electrochemical properties of both axial and helical derivatives and the possible generation of the corresponding radical compounds. Following this aspect, we deeper investigate the obtained SHI electronic configuration for these derivatives and take advantage of it to generate a persistent organic chiral diradical. C2-biaryl derivatives are largely employed as chiral ligands in synthesis, and more generally as chiral building blocks in materials, and supramolecular chemistry. The classical building blocks of this class are -bi(2-naphthol) (BINOL -bis(diphenylphosphino--binaphthalene (BINAP). These two compounds have been widely used in the last decade as homogeneous catalysts in an enormous number of asymmetric syntheses. [70] Besides the two main ligands, several alternative systems holding C2-biaryl core have been also developed such as BIFOL, [71] BIFAP, [72] BICOL, [73] and BICAP [74] (Figure 2

Bicarbazole system i. Definition

ii. Absolute configuration of BICOL a) CIP rules for absolute configuration of BICOL

Biaryl systems possess axial chirality (atropisomerism [75] ), which can be assigned their stereochemistry using CIP rules. Based on the latter, each aryl system is divided into two parts using a Newman projection and assigned a and b labels (the more important atom is always assigned to a). In the case of BICOL, after assigning the a and b priority, the sense of the operation a b will help to identify the Ra and Sa enantiomers, for clockwise and anti-clockwise operations, respectively (highlighted as the blue line, Figure 2345678910111213141516171819). In addition, the direct operation from a-a can be also assigned as the P or plus enantiomer and M or minus for clockwise and anticlockwise operation, respectively (highlighted as red line).

b) Exciton coupling and determining absolute configuration of biaryl system by ECD

A chromophore may be activated from its electronic ground state to an electronically excited state by the photon absorption with a matching wavelength to the energy gap between these states.

The spatial distribution of electron density in the excited state thus differs from that in the ground state. This creates an instant dipole, namely the electric transition dipole moment ( ), which is designated by a vector with an orientation corresponding to the direction of electron movement and a magnitude that is proportional to the intensity of the transition. [76] If two or more chromophores are close in the spatial arrangement, the electronic excitation is no longer confined to one chromophore and become interact between each other through space.

This phenomenon is termed exciton coupling. In the chiral environment, they interact with each other to split the excited states into two energy levels and generate two electronic transitions with a particular bisignature in the ECD spectrum. This phenomenon is widely used as an empirical method for determining the absolute configuration of various chiral compounds of natural and synthetic origin without the need for a reference system with a known configuration. [77][78][79] For instance, in the case of binaphthyl molecule, it is composed of two identical naphthalene subunits named by groups i and j and possessing intense transitions (ground state 0 excited state a), the coupling between these groups (i and j) results in a repel of two degenerated excited states into two energy levels ( and ) separated by energy (2Vij), namely Davydov splitting, while the fundamental state remains intact (Figure 2-20a and 2-20d). [77,[80][81] The rules of chirality of the exciton allow us to identify the configuration of each enantiomer (and therefore of the binaphthyl) according to the ECD response and the nature of the bands present.

The calculated ECD response for this process was rationalized by Di Bari, Pescitelli, and Salvadori in 1999. The presence of a positive band ( 250 nm, 1) and a negative band ( 220 nm,

2) indicates the S configuration of the binaphthyl system (Figure 2-20c). [77] In this case, the two electric dipole moments of transition along the major axis of two coupled chromophores rotate clockwise showing positive couplet (Figure 2-20e); for the other enantiomer, the sign of the Cotton effect is opposite, for instance, first, a positive band following by another negative band in lower energy region. The signature of the exciton coupling in the ECD spectrum allows us to determine the absolute configuration at the level of the coupled chromophores and therefore of the chiral biphenyl studied (Figure 2-23d). It is noteworthy to mention that the large dihedral angle may result in a sign inversion in the system as in 120 degrees due to the negative couplet. From the binaphthyl system, the absolute configuration of the BICOL can be determined in the same manner. As depicted in Figure 2-21, the ECD of BICOL showed the bisignate signal between 230 -270 nm similar to the binaphthylene model. [82][83] In this case, we can determine the absolute configuration of the BICOL system as R and S, by comparison with the structure band in this region to the binaphthalene model. iii. Examples of BICOL in the literature BICOL derivatives have attracted interest in a wide range of research domains, such as in biological applications, [84][85] chiral recognition, [82] as well as asymmetric synthesis [74,[86][87] . For instance, one of the natural BICOL derivatives, Sorazolon E2 1102 (dimeric sorazolon E, Figure 2-22) was successfully isolated from Sorangium cellulosum strain soce375, which shows cytotoxic and antibacterial activities. [84] Besides the biological properties, BICOL was also studied in chiral recognition with DNA. [82] Collins and Schmitzer reported a difference in the ECD response between the R and S enantiomer of BICOL in the presence of either b-DNA or z-DNA. Furthermore, Reek, Maarseveen, and Minnaard reported several BICOL-based ligands for asymmetric hydrogenation, which could achieve up to 98% ee (Figure 2-23). [74,[86][87]

iv. Synthesis access to BICOL derivatives

Regarding the synthesis aspect, the first BICOL derivative was introduced in 1989 by Moody and Shah upon the synthesis of carbazomycins. [88] The reduction of the ester group in The substituent-free BICOL synthetic route was introduced in 2002 by Heimstra et al. [73] This method starts from the Fisher indole reaction between cyclohexanone and p-methoxy- and there is also a formation of asymmetric dimer 117 in 15-20% yield (Scheme 2-2). This method was improved by Hoen using a catalytic amount of VO(acac)2 in the presence of molecular oxygen gave (±)-BICOL in a similar yield (Scheme 2-2, green path). [89] Scheme 2-2. Synthesis towards (±)-BICOL.

phenylhydrazine
Recently, another approach was reported by Pittelkow and co-workers starting from monodeprotection of 9-benzyl-3,6-dimethoxycarbazole 118 by BCl3. Then, an oxidative coupling between hydroxycarbazole 119 yielded BICOL derivative 120 in quantitative yield (Scheme 2-3). [90] Recently, Benavides, Jiménez-Vázquez, and co-workers reported a spontaneous dimerization of 122 upon hydrolysis of either Murrayanine (1-methoxy-9H-carbazole-3-carbaldehyde, 121a) or its formyl ester 121b in high yield (>85%, Scheme 2-3). [91] Scheme 2-3. Synthesis towards (±)-BICOL derivatives 120 and 122.

Along with the synthesis of BICOL, several options have been investigated to obtain the corresponding (+)-and (-)-enantiomers. For instance, Heimstra and co-workers reported chiral resolution methodology using menthyl group as a chiral auxiliary (Scheme 2-4). [73] The reaction between (±)-BICOL and (-)-menthyl chloroformate gave (±)-123 as a 1:1 diastereomeric ratio.

Then, recrystallization in diisopropyl ether gave crystals of (-)-123, which can be reduced to (+)-BICOL with LiAlH4 in 56% yield (Scheme 2-4). The (-)-BICOL can be obtained from the mother liquors, by firstly a treatment with LiAlH4, then a reaction with (+)-menthyl chloroformate enantiomer, and after a recrystallization step, a final reduction with LiAlH4 in 67% yield. Hoen also reported the separation of the obtained diastereomers using column chromatography, after hydrolysis of the ester group, can afford the two enantiomers. [89] Scheme 2-4. Chiral resolution of (±)-BICOL. i. (a dimer version of (S)-124). [92] The reaction in the presence of air allowed them to obtain 1112 with ee Ra,S,S)-1242 with Nsubstituted-3-hydroxy-9H-carbazoles, which could achieve chiral BICOL derivatives 126 with ee up to 80%. [93] Scheme 2-5. Enantioselective synthesis of BICOL derivatives 126.

Surprisingly, despite their ease of preparation, to the best of our knowledge, there was no report of any photophysical and chiroptical properties of BICOL derivatives until our study except the aforementioned ECD of BICOL (vide supra). This further reinforced our motivation to explore such systems, notably by considering their applications as a potential chiral backbone for a wide range of applications.

Preparation of BICOL derivatives and model carbazoles

The synthesis of the new BICOL derivatives was performed starting from the preparation of 3-methoxy-9H-carbazole 115 by direct functionalization of the carbazole backbone (Scheme 2-6). 3-Bromo-9H-carbazole 127 was obtained in quantitative yield by selective monobromination of 9H-carbazole using N-bromosuccinimide (NBS) at the 3-position. [94] Then, Ulmann coupling between 127 and sodium methoxide using stoichiometric amount of copper(I)bromide gave 115 in 80% yield. [95] Scheme 2-6. Schematic synthesis route towards 3-methoxy-9H-carbazole 115. Reaction conditions: (i) N-bromosuccinimide, .

3-Methoxycarbazole 115 was then demethylated and subject to an oxidative homocoupling reaction using vanadyl acetylacetonate as a -bicarbazole--diol, BICOL (Scheme 2-7). As mentioned above, BICOL can also be obtained using several other metal catalysts, including CuSO4/Al2CO3 [73] and VO(acac)2 [89] in a maximum of 45% yield with pure oxygen as an oxidant. For improving the reaction yield, several conditions were tested as described in Table 2-1. Indeed, using ambient airflow ( 22% O2 v/v) instead of pure oxygen did not lead to a full consumption of starting material within 24 hours, but, importantly, the BICOL selectivity increased to a maximum of 66% yield (entry 3) and the scale can be enlarged up to 2.4 g with the reaction yield staying in a range of 60% (entry 5). BICOL was firstly methylated at both the nitrogen and oxygen atoms using dimethyl sulfate in the presence of 22M NaOH to give rac-128. [94] rac-129 were obtained from BICOL through demethoxylation and subsequent bridging using diiodomethane in 70% yield. [96] Further methylation of 114 using the same strategy as 128 afforded N-methylated 128b quantitatively.

Structural study

X-Ray structures analysis provides further structural insights for rac-128 and rac-129, which crystallized in the P-1 and C2/c space groups, respectively (Figure 2-24b-c). Dihedral angles of 87.1 and 52.4 between the two carbazole units were measured for 128 and 129, respectively, in accordance with the former BICOL precursor (84.9 , respectively, Figure 2-24a) presenting axial chirality, while the torsion angle of 129 appeared to be reminiscent of the one found for carbo [6]helicene. [97][98][99] These structural differences were also confirmed by density functional theory (DFT) calculation (in collaboration with Prof. Jochen Autschbach and Dr. Laura Abella -University at Buffalo, State University of New York, USA). The dihedral angles between the carbazole units are 76.9 and 52.2 , respectively (Figure 2-24d-e). The difference in the dihedral angle between the two molecules affords a possibility to differentiate these compounds in terms of chirality. Since compound 129 adopts a helical structure, the term helical chirality can be used rather than axial chirality when one wat to address a difference with compound 128, presenting 90 angle arrangement between the two carbazoles. [100] All of these observations indicated that the electronic coupling between the two carbazole units of these chiral compounds should differ significantly depending on the dihedral angle, which may impact their corresponding photophysical, chiroptical, and electronic properties.

Specific and molar rotations

The specific and molar rotation of the enantiopure compounds were measured in comparison. [72] Compound Concentration (g mL -1 ) Solvent (10 -1 deg•cm The specific rotation of axial bicarbazole 128 appears to be close to the one measured for the BICOL precursor while helical bicarbazole 129 displays a six-fold higher specific rotation value.

The presence of the t-Bu groups resulted in a different specific rotation response. In axial bicarbazole 130, the specific rotation increased in comparison to the non-substituted one, suggesting a lower torsion angle in line with the optimized structure in solution (vide supra). For helical bicarbazole 131, the specific rotation decreases by half in comparison with the non-substituted one, suggesting a higher torsion angle in line with the crystal structure.

Neutral state photophysical and chiroptical properties

All the photophysical and chiroptical measurements of carbazoles 128b and 130b and ii. Electronic circular dichroism (ECD)

The binaphthyl and helicene-like systems (vide supra). [77,80,101]

iii. Fluorescence and circularly polarized luminescence (CPL) spectroscopy

The photoluminescence studies were conducted in dichloromethane at room temperature excitation = 370 nm) at a solution concentration of 10 -6 mol•L -1 . The emission profiles are depicted in respectively, in accordance with their measured gabs at 370 nm (gabs = 1.0, 1.7, 1.3, and 1.7 10 -3 , respectively) [102] , and the range of classical organic chiral emitters. [103] 250 300 350

Electrochemical properties

Cyclic voltammetry (CV) experiments were conducted on 128, 129, 128b and 130b to gain more insights into their electronic properties. All these monocarbazole and bicarbazole derivatives displayed two oxidation events between 0.95 and 1.60 V vs. SCE, which, however, present different responses in terms of reversibility. While compounds 128b and 129 showed two irreversible oxidation events at 0.95 V and 1.60 V, and 1.14 and 1.40 V, respectively (vs. SCE, 234567), compounds 128 and 130b display a first reversible oxidation event at 0.92 and 0.87 V, respectively, followed by a second non-reversible one at 1.11 and 1.63 V, respectively. These observed differences are rather surprising, especially for the first reversible oxidation of 128, since 3-and 6-unprotected carbazole derivatives form unstable radical cation under oxidative conditions. [104][105][106] This unusual aspect, as well as the marked difference of 200 mV with the first oxidation of 129, prompted us to further investigate the monoradical cation 128 + .

A 3-and 6-functionalized carbazole 130b was selected as a reference persistent carbazole radical cation thanks to its fully reversible oxidation process at 0.87 V vs. SCE (Figure 2-40). This allows us to assign the oxidation event of bicarbazole 128 at 0.92 V and 1.11 V (vs. SCE) as the first two oxidation processes corresponding to the oxidation of each carbazole unit while the third oxidation process corresponds to the second oxidation of a single carbazole unit (Scheme 2-10). The addition of AgBF4 as a chemical oxidant (EOx = 1.11 V vs SCE in dichloromethane) [107] to a solution of 130b in dichloromethane afforded a persistent monoradical 130b + BF4 -with a characteristic vibronic visible signature at 696 nm and 771 nm, as expected for 3,6-protected carbazole (Figure 2-37a, Scheme 2-11). [104][105] In the same conditions, 128 was quantitatively converted to 128 + BF4 -with a comparable optical signature to 130b + BF4 -(Figure 2 All spectra were measured in dichloromethane at 298 K.

Furthermore, UV-vis titration study of 128 and 129 by using (4-BrPh)3NSbCl6 (so-called magic blue, EOx = 1.16 V vs SCE in dichloromethane) [107] allows us to get further information regarding the possible degradation pathways of 128 and 129 (Figure 2-38). The addition of more than 1.0 equivalent of magic blue in a solution of 128 resulted in the appearance of a broad NIR band between 1000-1800 nm, similar to the one observed in compound 129, suggesting that an oligomerization also takes place for 128 + , but with a slower rate than 129 and led to a conclusion that 128 + is persistent. The similar optical and magnetic signatures of both 130b + BF4 -and 128 + BF4, and the absence of intense intervalence absorption transition for the latter, suggest the localization of the unpaired electron on one carbazole unit in 128 + BF4 -, and not delocalized across to the other molecular fragment as in organic mixed-valence compounds, which highlighted unprecedented stability of carbazole centered radical without any steric protection at the reactive 3-or 6position. [108][109] In addition to its high chemical stability, 128 + BF4 -remains also configurationally stable, owing probably to the high racemization barrier of its = 173.5 kJ mol -1 , 180 C -spin density -spin LUMO. As mentioned above, the SHI configuration has emerged as one of the stabilization factors for radicals, [12,46,[51][52]57,110] and our results suggest that such effects may be also responsible for the high stability of 128 + BF4 -. However, it is noteworthy to mention that 129 + BF4 -appeared experimentally unstable, despite an electronic configuration implying a SHI. This high stability difference represents a unique opportunity to explore further insights regarding the key parameters that lead to high radical stability with SHI configuration. Since the structures of 128 and 129 differ by the dihedral angle between the two carbazole systems, the difference of reactivity between 128 + and 129 + may be related to the electronic coupling between the radical center and the second neutral carbazole fragment. The photophysical and chiroptical characterizations, and the separation of the two first EOx, equal to 190 mV and 260 mV for 128 and 129, respectively, suggested that the electronic interaction is negligible for 128 (Figure 2-44). [108][109] In addition, the negative inductive effect induced by the meta-connection of the carbazolyl substituent toward the considered carbazole unit may more destabilize the radical 129 + than 128 + . This is experimentally confirmed between the HOMO and the SOMO (0.80 eV and 0.40 eV, respectively). Also, the energy difference between the HOMO of 129 and 129 + is 0.54 eV, much larger than the difference of 0.18 eV for 128 and 128 + , confirming the stronger interaction between the radical center and the second carbazole in 129 + (Figure 2-44). These results suggested that the electronic coupling between the radical center and the neutral electron-rich fragment has a crucial role in the stabilization of a molecular open-shell electronic state with SOMO-HOMO energy inversion. [12]

Consequence of the SHI: open-shell diradical upon oxidation

The SHI found for 128 + and 129 + provides an interesting opportunity to design novel organic diradicals with a high-spin ground-state. As illustrated in Interestingly, the reversibility of these oxidation processes was also enhanced in comparison to 128 + and 129 + , highlighting the impact of steric protection. Indeed, compound 130 displays full reversibility for both the first and second oxidation processes (EOx = 0.87 and 1.10 V vs. SCE) without any degradation after 50 cycling scans. On the other hand, while the first oxidation process of 131 exhibits a fully reversible response at 1.06 V vs. SCE, its second oxidation at 1.37 V shows less reversibility and leads to the appearance of a weak new reduction peak at 0.85 V in the reverse scan, suggesting some instability for diradical 131 2 2+ , as in the case of 128. The UV-vis-NIR spectra of monoradicals 130 + and 131 + were investigated using spectroelectrochemistry and exhibited similar radical absorption than 128 + in the UV-vis region but significant changes in the low energy part of the spectra (Figure 2-47). Both 130 + and 131 + have the corresponding NIR absorption bands red-shifted to 812 and 850 nm, respectively, and show less vibronic structure than 128 + . Additionally, the broad NIR band that extends up to 1300 nm for both radicals, appears more intense than for 128 + -1 cm -1 and 1100 M -1 cm -1 for 130 + and 131 + , respectively. These observed photophysical differences suggest that the spin is no longer localized on only one carbazole fragment for both 130 + and 131 + but interacts with the second fragment to some extent. Moreover, the electronic coupling between the two carbazoles seems (blue) forms. Selected transitions and oscillator strengths are showed high chiroptical properties in the NIR region, as indicated by its absorption anisotropy factors, gabs = 1.0 10 -3 at 920 nm (Figure 2-55b), which is one among the highest measured for molecular organic diradicals. [111][112] This observation represents one of the rare examples of stable intrinsically organic chiral diradicals and thus embedded unique magnetic and chiroptical properties. Corresponding (-) enantiomers marked with the grey line.

Air

The magnetic properties of 130 2 2+ •2SbCl6 -were investigated by EPR, which was unable to detect any signal at room temperature. The signal was gradually detectable below 150 K resulted in an intense and broad doublet without neither m = 2 transitions at halffield, presumably due to the long distance between the two nitrogen-centered radicals (g = 2.002, Figure 2-56, left). [113] Given the high stability of Interestingly, these findings did not confirm the triplet ground-state spin multiplicity that should arise from the oxidation of a monoradical with SHI. [6,57] Similarly, the calculations showed that 130 2 2+ has two unpaired electrons and a spin-triplet electronic state instead of a singlet configuration, including two -spin SOMOs and, below in energy, the set of spin-paired orbitals (Figure 2-54, vide supra). The isosurfaces of the two SOMOs (as well as for LUMO and LUMO+1)

were represented in-phase and out-of-phase linear combinations of frontier fragment orbitals with an energetic splitting of 0.13 eV, whose combined densities are reflected by the spin density calculations (Figure 2-54). However, spin state energetics are not easy to deal with in DFT calculations. We found that an open-shell singlet configuration became effectively iso-energetic with the triplet when the fractions of the exact exchange in the functional went to zero, and weak interactions between the electron spin in adjacent units of 130 2 2+ in the solid state may further complicate the picture. We thus hypothesize that given the weak electronic coupling between the carbazole fragments in 130 2 2+ •2SbCl6 -, the two SOMOs could be considered as disjoint, which ultimately favored singlet ground state, in analogy with previous 3,3 -Dimethylenebiphenyl diradicals molecular design and using Ovchinnikov parity models. [31,[114][115]

Conclusion

SOMO-HOMO inversion (SHI) is an uncommon electronic configuration of some open-shell

compounds where the singly occupied molecular orbital (SOMO) lies energetically below one or several doubly occupied molecular orbitals. This unique electronic configuration can be rationalized by incorporating computational and experimental evidence such as electrochemistry and the forming of the corresponding diradical species. The SHI configuration in radicals emerges as an additional feature to enhance their radical stability and is promising for potential applications in optoelectronic, spintronic, and magnetic devices.

Towards this direction, we have turned our attention to the C2-bicarbazole system, an analog of BINOL named BICOL, which has been used mainly for asymmetric catalysis, biological activity, and chiral recognition. We firstly revisited the synthesis of the BICOL backbone by direct functionalized the carbazoles and some derivatives by a late-stage functionalization strategy. Four new bicarbazole derivatives (128-131) along with the model compounds (128b and 130b) were synthesized and experimentally and theoretically investigated their structure-related properties base on the dihedral angle and system chirality, namely axial vs. helical.

We then investigated the electrochemical properties of both axial and helical bicarbazole derivatives, which highlighted a difference in reversibility of their oxidation processes, and described here the first sterically-free persistent axial chiral bicarbazole monoradical 128 , along with their photophysical, chiroptical, and magnetic properties. The persistent axial chiral bicarbazole monoradical 128 is chemically and configurationally stable, with a half-life up to 3 hours under air conditions, and the main decomposition pathway of 128 is decisively dedicated to oligomerization as observed by UV-vis-NIR spectroscopy and mass spectrometry detection. We attributed this unprecedented stability of this monoradical to an interplay between SOMO-HOMO inversion (SHI) and subtle electronic coupling between the radical center and the remaining neutral carbazole fragment, which directly linked to the carbazoles dihedral angle and related to axial and helical chirality.

Such unique electronic features provided an opportunity to obtain the first persistent, intrinsically chiral bicarbazole diradical 130 2 2+ , displaying near-infrared electronic circular dichroism intensity up to 1100 nm, highly persistent (more than 66 hours in solid state atand almost degenerate singlet-triplet ground states with weak antiferromagnetic interactions Chapter 3

Helical tetracarbazole radical cations: spin delocalization and SOMO-HOMO level inversion in the diradical state

This chapter is a part of publications Chapter 3: Helical tetracarbazole radical cations: spin delocalization and SOMO-HOMO level inversion in the diradical state

Summary

In the previous chapter, we have prepared and investigated a new chiral bicarbazole system with two different chiralities, namely axial vs. helical. The interplay between SOMO-HOMO inversion and electronic communication between the two carbazole fragments appear to be responsible for such unprecedented radical stability for the axial bicarbazole radical, while helical bicarbazole is unstable and kinetically oligomerized. In this chapter, we studied further the oligomerization process of carbazole and the possible extent to increase the radical stability of the helical bicarbazole.

Stabilization of helical bicarbazole could be achieved by introduction of two additional carbazole fragments. Tetracarbazoles 132 and 133 were prepared and their neutral state photophysical and chiroptical properties were investigated. We found that the difference in carbazole isomerism plays a role in the different photophysical and chiroptical properties. Additionally, their redox properties showed high reversibility, resulting in the highly persistent character of the subsequent monoradicals -connection between the two carbazole units.

Interestingly, we found that the electronic interaction between the molecular fragments and the

Extended carbazole oligomerization and potential of extended conjugated bicarbazoles

As explored in the previous chapter, the reactivity of the oxidized carbazole unit is rich and leads to various products depending on the reaction conditions and the substituent(s) on the carbazole fragments. [1][2] Indeed, the single electron oxidation of unsubstituted carbazole forms an unstable radical cation, which can further oligomerize at different positions through homocoupling reactions. [3] More precisely, when no (or only one) substituent is present at the 3-or 6-position of the carbazole molecule, oxidation of the latter generally affords the corresponding 3,3 -bicarbazole -bicarbazole) bicarbazole unit, which possesses a lower oxidation potential (easier to oxidize) and may present higher radical stability (pathway A). [4] However, if both positions 3-and 6-are functionalized by substituents, other than the hydrogen atoms, the dimerization of the oxidized carbazole will preferentially occur at 9-position to form the 9,9 -bicarbazyl fragments (Scheme 3-1, pathway B). Note, however, that the uncontrolled oligomerization process may result in a mixture of carbazole oligomers of several molecular sizes.

Scheme 3-1. Illustration of the main oligomerization products that can be obtained upn oxidation of the carbazole fragments.

Preparation of tetracarbazole derivatives and a bicarbazole model i. Stabilization of helical bicarbazole radicals

In the previous chapter, one of the identified decomposition pathways of unprotected axial Based on -bicarbazole radicals, [4] we thus wondered if it would be possible to control the oligomerization process and form new chiral dimers of bicarbazole systems with potentially higher stabilization for the mono-(and di-) radical state(s). Toward this purpose, we Given our results described in Chapter 2 and the recently reported method developed by Venkatakrishnan et al., [5] we firstly investigated the use of 2 Despite our attempts, this mixture appeared difficult to separate, especially due to the poor solubility of the racemic compounds. However, the potential formation of helical enantiomers for (R,S)-132b led us to further investigate the obtained compounds mixture by analytical chiral HPLC study (Figure 34, collaborated with N. Vanthuyne, Aix-Marseille University). The presence of three products was confirmed and tentatively assigned to the two enantiomers (+)-and ( )-132, and the mixture of meso compounds 132b. Moreover, this preliminary analytical study suggested that the latter show an additional chiral element, since two enantiomers can be detected, with a too weak racemization barrier to be isolated. With all this information in hands, we decided to perform the homocoupling reaction using directly enantiopure (+)-and ( )-129, which yielded only (+) or ( )-132 quantitatively (Scheme 3-3). As -bicarbazole 134 was synthesized as a model compound for comparison and rationalization of the final chiroptical and optoelectronic properties. We first attempted to perform an oxidative coupling starting from and using similar conditions as for compound 132. However, the reaction was not successful and led to several products, presumably bicarbazole isomers as presented in Scheme 3-1 (vide supra). Therefore, the Suzuki coupling approach was applied with a reaction between iodocarbazole 136 and boronate ester 137 in the same conditions than 133. After purification, compound 134 was obtained in 50% yield.

Structural study

Crystal structures were obtained for both 132 and 133, in their enantiopure and racemic forms, respectively, and as a co-crystal with dichloromethane for the latter. The dimers of bicarbazole (+)-132 and 133 structures were confirmed by X-ray crystallography, which crystallized in the P21 and P-1 space groups, respectively (Figure 3-5a-f -bicarbazole cores ( a) are found to be between 52-55 , a comparable value to the one of 129. Furthermore, a second dihedral angle is also observed at the -bicarbazoles fragments, which are in between 32-34 for 132 and at 47-50 ( b) for 133. Here, it is interesting to note that the relative orientation of -connection differs between the two compounds. Indeed, compound 132 presents a trans relation between the nitrogen atoms of the carbazole, similarly to the one found in the -bicarbazole x-ray structures ( b = 37 ), [5] while 133 shows a cis relation.

In addition, several CH-interactions can be identified between protons H 5 107 From this theoretical study, the conformer observed for 132 in the X-ray structure with the two external carbazoles pointed to the opposite direction appears not to be the most stable structure. In fact, three different conformers have been tested for carbazole dimer 132 Xray -affording -as the most stable one (Figure 34567). The 132 X-ray kcal•mol -1 higher in energy, which corresponds to Boltzmann populations of <0.5% at 298 K for both of them. This suggests that the more effective crystal packing favors the slightly less stable conformer in the solid state. The calculated properties of 132 further support the higher abundance of the -in solution by comparison with the experimental chiroptical properties (vide infra).

Specific and molar rotations

The specific and molar rotation of the enantiopure compounds were measured in CH2Cl2 The obtained values for 132 and 133 are of medium intensity for helical systems being not fully conjugated, in comparison to the specific optical rotation value of +3640 measured for P- [6]helicene (in CHCl3, 0.03 g mL -1 ). [6] Interestingly, the molar rotation of 133 is higher than for 132, further highlighting the impact of the structural difference between these two tetracarbazole compounds, and indicating a more intense interaction with polarized light in the case of the extended helical structure of 133. Both enantiomers showed close values of optical rotations with opposite signs as expected.

Neutral state photophysical and chiroptical properties

All the photophysical and chiroptical measurements of bicarbazole and tetracarbazole compounds have been measured in dichloromethane solution with concentrations in the range of -conjugated systems, including some contributions on the nitrogen and oxygen atoms, whereas the LUMO is only localized on the -conjugated system of one of the two -bicarbazole fragment (Table 3-3) -bicarbazole system, with a small energy difference of 0.120 eV. In the case of 133, the HOMO is mostly localized on the -orbitals of the two carbazole fragments at each extremity of the helix including the nitrogen and oxygen atoms -bicarbazole system, where the LUMO is exclusively localized. Compound 133 has quasi-degenerate HOMO and HOMO-1 levels, separated by 0.086 eV, Chapter 3: Helical tetracarbazole radical cations: spin delocalization and SOMO-HOMO level inversion in the diradical state 110 as expected from the weak electronic interaction between the peripheral methoxycarbazole units.

Indeed, visual inspection of the MO isosurface plots reveals that the HOMO-1 and HOMO are essentially in-phase and out-of-phase (+/-) linear combinations of individual carbazole fragment frontier orbitals (FFOs).

ii. Electronic circular dichroism (ECD)

The ECD spectra of enantiopure (+)-/( )-132 and (+)-/( )-133 further highlight the differences in terms of molecular frontier orbitals between the two compounds (Figure 3-10). Indeed, (+)-132 display a qualitatively similar ECD signature than (+)-129, with a positive exciton couplet around 260 nm, followed by two positive bands at ca. 280 and 315 nm ( = + 125 and + 238 M -1 cm -1 , respectively) and a negative broad vibrational band between 340 and 390 nm ( = -23 M -1 cm -1 ).

On the other hand, (+)-133 exhibit a different ECD response with a first intense negative band at 255 nm ( = -141 M -1 cm -1 ) and a broadly positive one with a maximum at 303 nm ( = + 100 M -1 cm -1 ) followed by a low energy positive couplet at 395 nm, very close to the typical ECD signature of carbohelicene derivatives. [7][8][9] The ECD spectra were also well reproduced by TD-DFT calculation for the most stable conformers (Figure 3-11).

iii. Fluorescence and circularly polarized luminescence (CPL) spectroscopy

The photoluminescence studies were conducted in dichloromethane solvent, at room excitation = 370 nm) with a solution concentration of 10 -6 mol•L -1 . The emission profiles are depicted in The CPL studies were recorded excitation = 370 nm in dichloromethane solution (ca. 10 -5 M). The CPL spectra are depicted in Figure 3-13a where each pair of enantiomers gave mirrorimage CPL spectra. They were normalized to 2 at the maximum of their corresponding photoluminescence spectra, which allow a direct lecture of the glum factor at this emission wavelength. Interestingly, while compound 132 showed a lower |glum| value of 1.2 10 -3 at 440 nm than its |gabs| value of (2.0 10 -3 at 362 nm), compound 133 showed a threefold higher |glum| factor at 465 nm than its |gabs| value at 405 nm (5.0 10 -3 in comparison to 1.7 10 -3 , Figure 3-13b).

The uncorrelated dissymmetric factors between the |gabs| and |glum| in 133 is observed for helicene-like system due to its greater excited-state relaxation despite the glum values of both compounds remain in the range of classical organic chiral emitters. [10][11]

Electrochemical properties

Cyclic voltammetry (CV) experiments of compounds 132 and 133 revealed multiple reversible oxidation processes related to the presence of the four carbazole units. In comparison to bicarbazole 129, which shows only two irreversible oxidation processes at +1.14 and +1.40 V, as classically observed for 3-and/or 6-unprotected carbazole derivatives, [3,5,12] 132 displays three oxidation events at 0.85, 1.17, and 1.30 V vs. SCE (Figure 3 Following electrochemical characterizations, we then investigated the chemical oxidation of our compounds and the reactivity of their corresponding monoradical products. The addition of 1 eq. tris(4-bromophenyl)ammoniumyl hexachloroantimonate (magic blue) as a chemical oxidant (EOx = +1.16 V vs. SCE) [13] The stability of the cationic monoradicals 132 + SbCl6 -, 133 + SbCl6 -, and 134 + SbCl6 - were followed by kinetic UV-vis-NIR analysis under air condition. The bicarbazole model 134 + SbCl6 -has been taken as a reference, which shows a second-order decay with a half-life value of about 7 hours in air-saturated atmosphere (Figure 3-16 and Table 34567). This appears two times lower than for 133 + SbCl6 -, around 15 hours, proving a higher stabilization by the presence of the -bicarbazole fragment. Unexpectedly, the stability of monoradical 132 + SbCl6 - dramatically increases to 6.5 days, which is rather high in comparison to 133 + SbCl6 -, and 134 + SbCl6 -, and highlights the impact of the molecular structure on the stability of these novel organic open-shell compounds. -bicarbazole unit involving two electronically connected redox-active nitrogen centers, we further investigated the impact of the solvent polarity in the optical signature of organic radical in the NIR region. [14][15] We tentatively characterized this aspect by recording the UV-vis-NIR spectra of in situ generated radical by magic blue oxidant in acetonitrile (EOx = +1.05 V vs. SCE) [13] (Scheme 3-8), representing a more polar solvent than dichloromethane. The UV-vis-NIR absorption spectrum of 132 + SbCl6 -in acetonitrile displays significant differences in comparison with the one obtained in dichloromethane, marked by a drastic decrease of the NIR band between 1000 and 2000 nm and to a less extend to the one at 410 and 550 nm, concomitantly to an 80 nm blue shift of the band at 970 nm, which now dominates the optical response in the low energy region (450-2000 nm, Figure 3-19a). This change clearly indicated that the spin delocalization in 132 is significantly altered with the solvent polarity, as classically observed for class II-III of organic mixed-valence (MV) compounds. [16] This is particularly interesting since rare examples of molecular chiral organic MV compounds have been reported, and electron transfer reactions involving chiral molecules have recently attracted strong interest for their ability to show chirality-induced spin-selectivity (CISS). [17][18][19][20] For comparison, the absorption spectrum of 133 + SbCl6 -and 134 + SbCl6 -is significantly less affected by the polarity of the solvent, but shows a similar evolution than 132 + SbCl6 -with a decrease in intensity of the overall NIR band and a comparative increase of the absorption between 800-900 nm for both 133 + SbCl6 - and 134 + SbCl6 -. These suggest a weaker electric dipole moment for the transition found at around 900 nm than in 132 + SbCl6 -, resulting in a less impact of the polarity of the solvent (Figure 3-19b and 3-19c). = + 3.0 M -1 cm -1 ), followed by broad negative one between 600 and 1000 nm ( = -2.0 M -1 cm - 1 ) while (+)-133 + SbCl6 -displays a positive signal at 460 nm ( = -1.1 M -1 cm -1 ), successively followed by a negative and positive ones at 510 and 580 nm ( = 0.5 M -1 cm -1 ), respectively, and finally a very broad positive band up to 1000 nm ( = + 2.3 M -1 cm -1 ). For both compounds, moving to acetonitrile solvent impacts the ECD responses with a 70 nm blue-shift of the Cotton effect found at 620 nm in dichloromethane for (+)-132 + SbCl6 -, and the appearance of a new Cotton effect at 940 nm for (+)-133 + SbCl6 -(Figure 3-22b). To the best of our knowledge, this is the first evidence of ECD sign inversion for chiral organic radicals in the function of the solvent polarity.

iv. SHI process in 132 + , 133 + , and 134 +

Taking 134 + as a reference, it is noteworthy to highlight a two-fold stability increase observed for 133 + upon dimerization at position 4. Although it is not inducing any significant -bicarbazole as indicated by the photophysical and electrochemical measurements, the presence of -dimer results in the formation of a helicalconjugated system and affords a novel example of chiral organic monoradical with SHI. Indeed, the first two oxidation events occurring for 133 -bicarbazole arm, which partially lift the pseudo-degeneracy of the HOMO in 133 + . Following our previous findings on bicarbazole models 129 + , 133 + , therefore, adopts the SHI electronic configuration since its SOMO becomes lower in energy than the remaining HOMO and HOMO-1 of the second non--bicarbazole fragment, partially isolated from the radical center owing to the dihedral angle of more than 50 between the two -systems. Our result then suggests that electronic effects, rather than a steric one, are major contributors to the enhanced stability when going from 134 + to 133 + since we have shown that additional steric protection on 129 + , such as t-butyl groups, was not a decisive factor for reaching radical stability.

Further theoretical analysis of the electronic configuration of model bicarbazole 134 + shows that its calculated spin densities are represented by spin-polarized Kohn-Sham (KS) systems where the -spin HOMO has a matching occupied -spin HOMO. The SOMO energy level of 134 + is indeed energetically lying below the -HOMO suggested the partial SHI system (Figure 3-24d).

On the contrary, 133 + showed SHI, and the -spin HOMO has a matching occupied -spin HOMO with both having very similar orbital energies. As mentioned in the previous studies, SHI has been claimed as a stabilizing factor for radicals, [21][22][23][24][25][26] and our results suggest that such effects may contribute for the stability of 133 + . A similar situation is also present in 132 + with a less orbital energy gap E between the HOMO and the SOMO, of 0.24 eV compared to 0.60 eV for 133 + .

This can be explained by the stronger interaction between the radical center and the peripheral carbazole units in 132 + as indicated by the superior energy difference between the HOMO of 132 and 132 + of ca. 0.80 eV, much larger than the difference of 0.31 eV for 133 and 133 + . Given the much higher stability for 132 + , this result is counter-intuitive if we take into account only the SHI effect. Our results rather suggest a synergetic effect between the electronic delocalization of the unpaired electron and the SHI. Indeed, 1 H NMR and photophysical characterization have indicated that the external carbazole units in 132 interact more -bicarbazole fragment than in 133, and calculations on 132 + have shown that the SOMO is also delocalized over these peripheral electron-rich units.

Diradicals of 132 , 133 , and 134 i. Model bicarbazole diradical 134

The partial SHI observed for the model bicarbazole 134 allows us to further investigate the possibility to generate diradical species with potentially triplet ground state, as predicted by theoretical calculation suggested from the partial SHI of 134 (Figure 3-25c). The addition of two equivalents of magic blue oxidant into a dichloromethane solution of 134 under argon did not result in a diradical species, since the obtained UV-vis-NIR spectrum shows only the formation of the monoradical 134 with an optical signature of the excess of magic blue, suggesting the latter is not appropriate to lead the diradical formation. As a result, we turned our attention to AgBF4

(EOx = 1.11 V vs. SCE) [13] , as an inorganic oxidant, which was used with success in the previous as expected for the partial SHI compound (Figure 3-25c). [27][28][29] In dichloromethane, the obtained absorption spectra appear similar to the respective monoradicals 132 + SbCl6 -and 133 + SbCl6 -with however a superior absorption intensity. For 132 2 2+ •2SbCl6 -, the overall absorption band is more structured with two visible peaks at 430 and 550 nm ( 1 × 10 4 and 1 × 10 3 M -1 cm -1 , respectively) and three NIR peaks at 950, 1420 and 1750 nm ( 0.5 -0.8 × 10 -4 M -1 cm -1 ). In the same manner, 133 2 2+ •2SbCl6 -is also more structured similarly to model bicarbazole radical 134 + SbCl6 -but red-shifted compared to 132 2 2+ •2SbCl6 - with three visible peaks at 425, 550 and 690 nm ( 1.5 × 10 4 and 0.3-0.4 × 10 -3 M -1 cm -1 , respectively) and three NIR peaks at 1000, 1320 and 1875 nm ( 0.9 1.4 × 10 4 M -1 cm -1 ). In the more polar solvent, acetonitrile, the formation of 133 2 2+ •2SbCl6 -depicted a similar trend as a monoradical with a more intense signal between 600 and 2000 nm ( 6 × 10 3 M -1 cm -1 , Figure 3-26d). Contrary to the others, the formation of 132 2 2+ •2SbCl6 -in acetonitrile depicted a significant difference with an intense band at 900 nm ( 5 × 10 3 M -1 cm -1 ) and a moderate broad absorption band center at 1400 nm ( 4 × 10 3 M -1 cm -1 , Figure 3 The stability of these diradicals was measured by kinetic UV-vis-NIR analysis under argon, by taking the ratio between two absorption bands to get accurate results (Figure 3-29 3-32). [30] The evolution of the ratios can be fitted following two different regimes (marked as fast and slow) decays where the half-life time values (t1/2) of the diradicals can be estimated from the intersection between these two linear fittings. As a result, overall t1/2 values of both diradicals in dichloromethane are higher than in acetonitrile (Figure 3

iii. Conformational analysis and SHI in diradical states

In the diradical -bicarbazole system, the torsion angle between the two carbazole fragments tends to decrease and results in more planarity of the system, which may lead to a conformation change in the diradical system. [31] The calculated spin density of all diradicals suggested that the electronic ground states of them are spin-triplet ground state, where 132 2+ , the spin--remains to be the lowest in energy (Boltzmann population at 298 K of 98.2%), followed by the spin---1 (Boltzmann population at 298 K of 1.7%). In the case of 133 2+ , the spin-triplet conformer has changed from the neutral one with a flip of peripheral carbazoles from syn-to anti-formation regarding the adjacent nitrogen center (Boltzmann population at 298 K of 99.5%) while the 133 2+ with the same conformer as neutral has calculated relative energy at 3.1 kcal•mol -1 (Boltzmann population at 298 K of 0.5%, Figure 3-33). For both 132 2+ and 133 2+ , the doubly oxidized species have two unpaired electrons and a spin-triplet electronic state instead of a singlet state configuration. Accordingly, there are two -spin SOMOs, and spin density calculations reflect the combined densities of LUMO and LUMO+1 (Figure 3-33). For 133 2+ , the isosurfaces of the two SOMOs (as well as for LUMO and LUMO+1) are seen to represent in-phase and out-of-phase linear combinations of fragment frontier orbitals (FFOs) with an energetic splitting of 0.12 eV, and one of the SOMO energy levels is lying -HOMO, proving a partial SHI (Figure 3-34). In the extreme case, the two SOMOs of 132 2+ lie lower than the HOMO energy level with the higher energetic splitting of the two SOMOs at 0.72 eV thus suggesting the rare example of SHI electronic configuration in diradical. [32] Interestingly, while the electron density of the HOMO energy level of 133 2+ distributes over the entire the molecule, the electron density of the HOMO energy level of 132 2+ locates only in the remaining carbazole units suggesting the difference in electronic coupling in the two diradicals, which is similar as the monoradical of bicarbazoles 128 + and 129 + in the previous chapter (see Figure 2-44) and also suggesting the co-responsibility for the higher stability in 132 2+ than in 128 which can be assigned to radical absorption transitions at 550 and 610-950 nm in dichloromethane = +2.3 and 2.3 M -1 cm -1 , respectively, Figure 3-35a). In the same manner, (+)-132 2 2+ •2SbCl6 -also showed the same trend compared to its monoradical with radical absorption transitions at 520, 525, and a broad signal up to 1000 nm ( = +3.6, 0.8 and +5.0 M -1 cm -1 , respectively, Figure 3-35b). A similar trend was also observed in acetonitrile. The change in the polarity did not change any response from the corresponding monoradicals, in which the maximum was observed in 132 2 2+ •2SbCl6 -( +5.0 M -1 cm -1 at 850 nm). The ECD signal inversion remains presented in 133 2 2+ •2SbCl6 -with the 2.0 M -1 cm -1 at 850 nm compared to +3.0 M -1 cm -1 at the same wavelength in dichloromethane (Figure 3-35c-d). Importantly, diradical 132 2 2+ •2SbCl6 -showed its absorption anisotropy factors, gabs = 1.0 10 -3 between 700-900 nm, which is among the highest measured for molecular organic diradicals. [29,33]

v. Magnetic properties of diradicals

The magnetic properties of 132 2 2+ •2SbCl6 -and 133 2 2+ •2SbCl6 -were investigated by EPR experiments. An intense and broad EPR doublet signal was observed in dichloromethane solution at room and low temperature (77 K) and different from their corresponding monoradicals,

with g e = 2.00 (Figure 3-36, 3-37a, and 3-37b), as typically observed for all the radicals of the series. [34] The magnetic properties of both compounds were further investigated by variabletemperature (VT) EPR measurements, displaying a decrease in signal intensity (I) in frozen dichloromethane solution while lowering the temperature (T), indicating an antiferromagnetic singlet ground state for both diradicals. Fitting the VT-EPR data using the Bleaney Bowers equation [35] gave a singlet-triplet energy gap ( ES-T) of -1.19 and -1.37 kcal mol -1 for 132 2 2+ •2SbCl6 -and 133 2 2+ •2SbCl6 -, respectively (Figure 3-36c), which is slightly larger than that of 130 2 2+ •2SbCl6 -in the previous studies. In fact, these findings did not confirm the expected triplet ground-state spin multiplicity that should arise from the oxidation of a monoradical with a SHI. [24,36] We hypothesized that, given the longer distance between the two radicals than 130 2 2+ , the two SOMOs could be also considered as either disjoint or communicated by weak electronic coupling similar to the one we observed in the previous chapter. [37][38][39] 130 Corresponding monoradicals were shown in dash lines.

Conclusion

The knowledge acquired from the SHI and stability of carbazole radical cation was successfully applied for stabilizing the unstable helical bicarbazoles. By the addition of two carbazole fragments at 6-position, we successfully prepared a series of tetracarbazoles 132 and 133.

Compound 132, which possesses two chiral centers, was efficiently synthesized by an oxidative coupling reaction with enantiopure starting material, while 133 was obtained through Suzuki-Miyaura coupling with the 3-methoxy-9-methyl-9H-carbazoleboronic acid pinacol ester. These two compounds were investigated through their X-ray crystallographic structure, NMR, photophysical, and chiroptical spectroscopy and compared with the two bicarbazole models 129 and 134.

Interestingly, enantiopure 133 exhibits a high |glum| factor 5 × 10 -3 , which is twice higher than its corresponding |gabs|.

Chapter 4 -Chiral diindenocarbazole diradicals with SHI: A possible direction towards stable chiral triradicals 4.1 Summary

In the previous chapters, we prepared and investigated a series of chiral organic mono-and diradical cations based on bicarbazole and tetracarbazole systems. [1] We notably investigated their electronic, photophysical and chiroptical properties both for the neutral and radical forms.

Interestingly, a SOMO-HOMO inversion occurs in the electronic configuration of some of these open-shell compounds, inducing a further persistent character, while opening a new synthetic access to the formation of open-shell di-and poly-radical derivatives. While these examples have been developed only on carbazole-based radicals, the inherent cationic nature of the later complicates the isolation and characterization of the radical compounds, and may not be the ideal materials for possible device applications. To overcome this issue, we turned our attention to a neutral spin center, the fluorenyl-based one, representing the archetypal class of carbon-centered radicals.

Among organic radicals, carbon-centered radicals are attractive because of their trivalent nature, enabling diverse structural designs. However, they are often less stable due to their reactivity towards atmospheric oxygen, and their strong ability to form carbon-carbon bond. [2] It is appealing to continue our investigation on organic chiral radicals by investigating the potential of SHI in increasing the stabilization of carbon-centered radicals, and particularly the fluorenyl one, which represents the carbon analog of carbazole. Our approach is to create a cyclopentadienyl ring connecting to a carbazole backbone, namely indenocarbazole. Accordingly, compounds 155a and 155b were firstly synthesized and investigated to find the optimal conditions for generating radical 157 and 161 and use it as a reference compound. Then, we prepared the diindenocarbazoles 172 and 173, where the chirality comes from an inherent aza [5]helicene core with steric repulsion from the two mesityl groups. Only one diastereomer 173 afforded a subsequent bisfluorenyl-diradical with moderate persistent character measurable for 7 days and antiferromagnetic interaction (with ES-T 0.10 kcal mol -1 ) evaluated by VT-EPR spectroscopy.

Introduction to fluorenyl-based radicals

Fluorenyl radicals are a class of carbon-centered radicals, that have a similar structure to carbazole where the nitrogen atom is replaced by a carbon one. Fluorenyl is also a structural isomer of phenalenyl radical. However, unlike phenalenyl, half of the spin density is mainly localized at the 9-position of the fluorenyl radical, similarly to cationic carbazole radical one (Figure 4-1). [2][3][4][5] For 136 this reason, the exploration of stable fluorenyl radicals has been a challenge for many years, but recent attempts to stabilize fluorenyl radicals through -conjugation at the 9-position have shown interesting potential for the design and study of this persistent class of radical compounds.

i. Fluorenyl-based monoradicals

Generally, fluorenyl radicals can only be isolated when a large steric hindrance is present at the 9-position, with 9-anthryl, mesityl (2,4,6-trimethylphenyl), and alkynyl groups as classical examples of this strategy. In 2012, Wu, Casado, et al. reported the stabilization of fluorenyl radical 138 using the 10 -aryl-9-anthryl group, which afforded such a high kinetic stabilization that the radical can be purified by column chromatography over silica gel (Figure 4-2). [6] In the meantime, Swager et al. reported the stabilization of fluorenyl radical 139 using mesityl groups in a truxene-5-yl core. [7] The steric protection of mesityl units and delocalization of the unpaired electron over the -conjugated system provided 139 with a half-life time of 5.8 h under air conditions. The decomposition process of 139 has been associated to its reactivity with molecular oxygen using mass spectrometry characterization. In 2014, Kubo and co-workers studied the effect of extended benzannulation at different positions on the stability of fluorenyl radicals 140a-c (Figure 4-3). [8] The different double-bond characters of the obtained compounds afforded differences in redox potentials and absorption spectra, where 140a and 140c were more cyclopentadienyls in structure, while 140b favored a radialene structure. The difference in the structures has also impacts on their reactivity towards decomposition, as indicated by half-lives of 7, 3.5, and 43 days, reported in air-saturated toluene solutions under ambient conditions for 140a, 140b, and 140c, respectively, thus suggesting the importance of cyclopentadienyl character. Fluorenyl radicals with alkynyl substituent were also studied by Wu et al. [9] The 9ethynylfluorenyls 141a-c readily underwent intermolecular coupling giving either head-to-tail dimer 142 or head-to-head dimer 143 depending on the terminal substituents (Figure 4-4). Substitution with oxasmaragdyrin at a meso-position provided stable fluorenyl radical 144, which could be separated by silica gel column chromatography and which displayed a half-life value under ambient conditions of 226 h (Figure 45). [10]

ii. Fluorenyl-based diradicals and diradicaloids

Fluorenyl-based diradicals with a pure open-shell ground-state structure correspond to a rare class of compounds due to their high tendency to form diradicaloid structures. In 2012, Wu, Casado, et al. reported the first ground state fluorenyl-based diradical 145, interconnected through two anthryl groups, affording both high stability and limited electronic interaction between the two radical centers (Figure 456). [6] It presents a triplet ground state, as indicated by SQUID experiment, without any obvious decomposition under air and light conditions for months. Campos et al. reported a similar molecular design by using only one acene group 146a-c. [11] The formation of radical resulted in a diradicaloid ground state where the acene fragments exhibits either a bent 138 or butterfly-like quinoid structure. They exhibited aggregation-induced emission (AIE) in their quinoid structure as expected for a closed-shell molecular system. Thermal activated open-shell state switching was observed only for compound 146a due to a difference in aromaticity of the inner acene substituent. In 2018, Zeng reported an example of helically shaped fluorenyl-based diradical 147 (Figure 4-7a). [12] The molecule has highly twisted cyclobutenyl ring as a bridge connected to two indenofluorene radical units. The two latters afford a diradical compound with a singlet groundstate configuration, and not a closed-shell quinoidal structure. A S-T values (-0.53 kcal mol - 1 ) was calculated, which was confirmed by the observed forbidden transition s = 2) in the EPR measurement suggesting also a high diradical character. However, this compound appears particularly sensitive to oxygen, with the formation of furan unit to form 148, as a major decomposition pathway of the compound. backbone between them affording diradicaloids such as indenofluorene [13] , diindenonaphthalene [14- 17] , diindenoantracene [18][19] , and chiral helical-indenopicene [20] (Figure 45678). They often possess high stability in the closed-shell configuration, and their properties can be tuned by the peripheral connection at both terminal aromatic rings, as well as -conjugated unit between the two radical centers. By the oxidation approach, fluorenyl radical can be generated through a dehydrogenation-oxidation using either 2,3-dicyano-5,6-dichlorobenzo-1,4-benzoquinone (DDQ) or t-BuOK (Scheme 4-1a). [8,20] On the other hand, the reduction approach is based on the use of SnCl2 to reduce a hydroxy precursor (Scheme 4-1b).

Synthesis of indenocarbazole radicals i. Synthesis and structural characterizations

Our first attempt toward the synthesis of a chiral diindenocarbazole radical has relied on the extension of the carbazole -conjugated system by the introduction of an indene moiety. In this regard, two indenocarbazole derivatives were targeted, bearing for one of them an additional methyl group at the 11-position 155a and 155b (Scheme 4-2). The synthesis involved a Suzuki-Miyaura coupling between the 6-iodo-3-methoxy-9-methyl-9H-carbazole 136 and 2-formylphenylboronic acid, which afforded carbazole-aldehyde precursor 153a in 50% yield. Then, a Grignard reaction of 153a with 2-mesitylmagnesium bromide followed by subsequent Friedel Crafts alkylation reaction involving by BF3•OEt2 as a Lewis catalyst gave indenocarbazole 155a in 80% yield. Replacing the boronic acid coupling partner by 2-formyl-5-methylphenylboronic acid pinacol ester 160, and following the same synthetic strategy as for 155a afforded 155b in an overall of 30% yield.

ii. Photophysical and chiroptical characterizations

The photophysical and chiroptical spectra of indenocarbazole 155a and 155b were recorded in dichloromethane solutions with concentrations in the range of 10 followed by two positive bands at 250 and 300 nm ( + 15 and + 5 M -1 •cm -1 , respectively) and a low-energy negative one between 315 and 350 nm ( + 2 M -1 cm -1 ). Due to such low signal intensity in ECD, we could not obtain any CPL signal, which probably fall below the detection limit of our instrument. The presence of the methyl group in (+) and (-)-155b induced only a small overall red-shift of few nm in accordance with UV-vis and fluorescence spectroscopies.

iii. Electrochemical properties and chemically radical generation of indenocarbazoles

Cyclic voltammetry (CV) experiments were conducted on 155a and 155b to gain more insights into their electroactive properties. Both indenocarbazoles 155a and 155b depicted two reversible oxidation events at 0.92 and 1.63 V vs. SCE in dichloromethane, similar to the 3-and 6functionalized carbazole 130b (Figure 4-15), suggesting the highly persistent the character of carbazole radical and allowing us to study further the generation of fluorenyl radical. 144

The attempt to generate fluorenyl radical 157 was carried out via dehydrogenationoxidation reaction using DDQ as an oxidant in dichloromethane (Scheme 4-3). The formation of radical was obtained, afforded as a green solution. However, it was easily oxidized to pquinonemethide 158 upon purification through column chromatography, as indicated by 1 H-NMR, 13 145

In addition to the loss of chirality, the formation of 158 was also confirmed by 13 C-NMR as the presence of C=O bond signature around 180 ppm (Figure 4-18), and LRMS measurement was also detected molecular mass of 431 g mol -1 , which is equal to [157+O] (Figure 45678910111213141516171819). Thus, we turned our attention to the protected indenocarbazole 155b, where the methyl group was substituted in position 12 to protect the possible oxidized species.

b) Photophysical and chiroptical characterizations

The photophysical and chiroptical measurements of diindenocarbazole 172 and 173 were performed in dichloromethane solutions with concentrations in the range of 10 -5 -1 . UV-vis spectra appeared to be similar for both diastereomers, which depicted two maxima absorption at and a negative -7 M -1 •cm -1 ). The CPL studies were recorded with excitation = 350 nm in dichloromethane solution (ca. 10 -5 M). Enantiomers of 172 depicted a mirrorimage signal with |glum| about 4 × 10 -4 at 385 nm, which is in agreement with the obtained gabs. [22] In contrast, we could not record CPL spectra for 173 presumably due to the lower |gabs| value (2 × 10 -4 at 340 nm), which is lower than the limit of detection of our instrument (Figure 4-30b).

c) Magnetic properties

The magnetic properties of 173 2 were investigated by EPR on a fresh solution of the purified radical. Intense and structured EPR signals were observed in a dichloromethane solution at room temperature and even at low temperature (77 K) with g = 2.00 (Figure 4-33a). The magnetic properties of 173 2 were further investigated by VT-EPR measurements, and the signal intensity (I) in frozen DCM solution gradually decreased as the temperature (T) was lowered, which is consistent with its antiferromagnetic singlet ground state. Fitting of the VT-EPR data using the Bleaney Bowers equation [23] gave a small singlet-S-T) of -0.10 kcal mol -1 (Figure 4-33b). Further validation of the presence of diradical is currently investigating.

Conclusion and perspectives

The concepts developed through the previous projects on the construction of chiral organic radicals with SHI electronic configuration were applied to carbon-centered radicals. Two indenocarbazole models 155a and 155b were synthesized and characterized, which are moderately reactive and subsequently oxygenated. To provide chirality to the system, diindenocarbazoles 172 and 173 were synthesized as diastereomers and we attempted to generate diradical species. However, only compound 173 provided the diradical species with highly persistent character in solution under argon and antiferromagnetic singlet S-T = -0.10 kcal•mol -1 .

From the observed properties of diradical species, it would be interesting to explore further the possibility to generate triradical species by oxidation of the carbazole as depicted in the electrochemistry of the hydrogenated species (155a, 155b, and 173). A preliminary experiment by the addition of magic blue portions into the diradical 173 depicted an increment of the carbazole radical signature at 1000 nm with some extended NIR band suggesting the possibility to reach triradical species, and also an indirect proof of the presence of SHI in the system (Figure 4 As an extension to the knowledge acquired in this topic at the molecular level, the novel hybrid materials based on attaching organic radicals on surfaces have attracted attention to materials scientists, since the wide range of applications has been foreseen. From our system, it could be interesting to replace the N-methyl group with an anchoring unit such as a silane unit and immobilize it on a surface (Figure 4 -35). By this approach, it will open further opportunities for several applications such as spin probes, spin labels, electrocatalysis, electric transport, and spintronics. [24] Combining with the existing chirality in the system, it provides further potential to study the chiral-induced spin-selectivity (CISS) effect. Persistent radical cations with SHI showed a promising opportunity to stabilize carboncentered radicals. However, the stability issue of this radical class remains present and limited to a few reports. [4] The last project aimed to extend the SHI feature to the neutral carbon-center radicals based on the indenocarbazole system. We have prepared indenocarbazole 155 and characterized the presence of the fluorenyl-based radicals 157 and 164, which are highly reactive and subsequently oxygenated. Then, diindenocarbazoles 172 and 173 were prepared as diastereomers and attempted to generate diradical species (Figure B-3). However, only compound 173 provided an access to the diradical species with highly persistent character in solution measurable for 7 days under argon and S-T = -0.10 kcal mol -1 . Based on the result acquired in this thesis, several opportunities could be envisioned. First, the development of chiral luminescent radicals should be carried out. The luminescence radicals based on PTM-CBzs have shown to display its photostability associated with SHI. [5] In this regard, since the BICOLs also enclose SHI, the combination between BICOL and other luminescent radical units may provide chirality into the system. Incorporated with exciton coupling, it may bring such high stability and chiroptical properties. Furthermore, the observed properties based on helical bicarbazole may also provide further opportunities to fabricate OFETs and measure the conductivity within the chiral environment.

While the chiral luminescence radicals have provided such opportunities towards future optoelectronic devices, the interaction between the chirality and spin on the surface is also promising. The extended structure from the BICOL backbone with an anchoring unit may also imply and use for studying such interaction on the surface such as indium-thin oxide (ITO), fluorinedoped tin oxide (FTO), glassy carbon electrode, and silicon surface. Such functionalized structures may be interesting regarding possible spin-filters applications or chiroptical sensing due to the presence of spin and chirality. Besides these applications related to chiral organic radicals, the BICOL backbone is also providing further opportunities to modulate itself, since this molecular backbone received little attention and limited to a few applications. Our group recently reported the first donor-acceptor system based on BICOL backbone with a notably strong increase of the luminescence dissymmetry factor, glum, for the helical donor-acceptor compounds related to a subtle reorganization of the intramolecular charge-transfer process, [6][7] which could take benefit from the chiroptical features of BICOL for further applications. ). NMR analysis of BICOL was in accordance with literature. [3] (±)--Dimethoxy--bis-(9-methyl-9H-carbazole) -128 [1] In a pre-dried Schlenk flask, 300 mg (0.82 mmol) of (±)-BICOL were dissolved in 25 mL of acetone under inert atmosphere. Sodium hydroxide (22 M aq, 0.88 mL, 20 eq) was added and the reaction mixture was stirred for 5 minutes at room temperature before being heated to reflux. Then 2.75 mL of dimethylsulfate (24.6 mmol, 30 eq) were added and the reaction mixture was further refluxed for 2 h. After cooling down to room temperature, the reaction solution was poured into 20 mL dichloromethane and washed with water (2 x 30 mL) and brine (1 x 30 mL). The organic phase was dried over anhydrous MgSO4, and the solvents evaporated under reduced pressure. The crude product was passed through a short silica plug (n-heptane/CH2Cl2, 1:1 as eluent) to yield 270 mg (77 % yield) of 128 as an off-white solid. HR-MS Bruker MaXis 4G, ESI (+), CH3OH/CH2Cl2 (90/10); ion [M+Na] + , C28H24N2O2Na, m/z (±)--Methylenedioxy--bis-(9-methyl-9H-carbazole) -129 [1,4] Boron tribromide (1 M in dichloromethane, 0.6 mmol, 6 eq) was slowly added to a solution of (+)-or (-)-128 (35 mg, 0.100 mmol) in dry dichloromethane (5 mL) at room temperature and stirred for 3 h. The organic phase was diluted and washed with water, then dried over MgSO4, filtered, and evaporated under pressure. The obtained solid was dissolved in 30 mL of acetone and transferred to a pre-dried Schlenk flask under argon. Potassium carbonate (150 mg, 10 eq.) was added. The reaction mixture was stirred for 5 minutes at room temperature before being heated to reflux. Then, 20 µL of diiodomethane (0.300 mmoL, 3 eq) was added and the solution further refluxed for 16 h. The reaction mixture was allowed to cool down to room temperature and the medium was diluted with EtOAc. The mixture was then washed with water (2 x 30 mL) and brine

(1 x 30 mL). The organic phase was dried over anhydrous MgSO4, and the solvents evaporated under reduced pressure. The crude mixture was passed through a silica plug (n-heptane/CH2Cl2, 1:1 as eluent) to yield 34 mg (90 % yield) of (+)-129 or 35 mg (93 % yield) of (-)-129 as off-white solids.

1 H NMR (400 MHz, CDCl3 (±)--Dimethoxy--di(1,1-dimethylethyl)--bis-(9-methyl-9H-carbazole) -130 [5] Compound 128 (150 mg, 0.48 mmol) was dissolved in nitromethane (9 mL) under argon.

Then, anhydrous zinc chloride (150 mg, 3 eq.) followed by t-BuCl (120 µL), were added, and the reaction mixture stirred for 16 h under argon atmosphere. Then, water was poured into the mixture and the organic layer extracted with dichloromethane (3 x 10 mL). The organic phase was washed with water, saturated NaHCO3, and brine (1 × 10 mL). The organic phase was dried over anhydrous MgSO4, and the solvent evaporated under reduced pressure. The crude mixture was passed through a silica plug (n-heptane/CH2Cl2, 1:1 as eluent) to yield 190 mg (quantitative yield) of 130 as an off-white solid.

3-Methoxy-9-methyl-9H-carbazole -128b

A stirred solution of 3-methoxy-9H-carbazole (200 mg, 1.01 mmol) was dissolved in 5 mL of acetone under inert atmosphere. Sodium hydroxide (22 M aq, 0.05 mL) was added, and the solution was stirred for 5 minutes at room temperature. The reaction mixture was then heated to reflux, before 1.5 mL of dimethylsulfate (15 mmoL, 15 eq) was added. The reaction mixture was further refluxed for 2 h. After cooling down to room temperature, the reaction solution was poured into 20 mL dichloromethane and washed with water (2 x 30 mL) and brine (1 x 30 mL). The organic phase was dried over anhydrous MgSO4, and the solvents evaporated under reduced pressure. The crude product was passed through a short silica plug (n-heptane/CH2Cl2 , 1:1 as eluent) to yield 200 mg (93% yield) of 128b as a white solid. [7] Trifluoroacetic acid (1 mL) was added to a solution of 300 mg (+) or (-)-129 (0.74 mmol) in dichloromethane (30 mL) and stirred for 5 minutes at room temperature. Then, 336 mg of DDQ (2 eq.) were added. After stirring at room temperature until full consumption of starting material, monitored by TLC, NaHCO3 s added to the resulting mixture, which was stirred for an additional 10 minutes. The organic phase was then extracted, washed with NaHCO3 and brine, dried over anhydrous MgSO4, and evaporated under reduced pressure. The resulting solution was filtered through a silica short plug (n-heptane/EtOAc 4:6 as eluent) to give (+)/(-)-132 in 300 mg (quantitative yield). [8] In a round bottom flask, a mixture of helical bicarbazole 129 (100 mg, 0.25 mmol) in CHCl3/CH3COOH (6:3 ml) was stirred at 0 C under argon. N-iodosuccinimide (101 mg, 1.8 eq.)

was slowly added, and the solution was stirred at 0 C. After 1 hour (the reaction was followed by thin-layer chromatography), the resulting mixture was purified through a short silica plug (CHCl3 as eluent). Compound 135 was finally obtained as a white solid in (130 mg, 80% yield). The product was directly used without further characterization except 1 H NMR. ). NMR analysis of 136 was in accordance with literature. [9] 3-Methoxy-9-methyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole -137

To a pre-dried Schlenk flask, 0.87 g (3 eq.) of potassium acetate and 0.90 g (1.2 eq.) of bis(pinacolato)diborane were added to a solution of 136 (1.0 g, 3 mmol) in 12 mL dimethylsulfoxide (DMSO) under inert atmosphere. Then, 100 mg of Pd(dppf)Cl2 (0.1 eq) were added, and the solution was resulting mixture was poured into water and extracted with ethyl acetate. The combined organic phase was washed with water and brine, dried over anhydrous MgSO4, and evaporated under reduced pressure. The crude product was filtered over a silica plug (n-heptane/CH2Cl2, 9:1 as eluent) and obtained as a white solid in 0.87 g (quantitative yield). The product was directly used without further characterization except 1 H NMR. To a pre-dried Schlenk flask, 80 mg (3 eq.) of potassium carbonate and of 136 (55 mg, 0.16 mmol) were added to a solution of 137 (50 mg, 3 eq.) in a mixture of 6 mL dimethylformamide and 2 mL water. Then, the solution was purged with argon for 15 minutes. To this pre-purged mixture, ). NMR analysis of 160 was in accordance with literature. [8] 12-Mesityl-2-methoxy-5-methyl-5,12-dihydroindeno[1,2-c]carbazole-155a [10] To a solution of compound 153a (160 mg, 0. (-)-155a: = +1550 ± 1%, = +6500 (c = 4.2 10 -3 , CH2Cl2).

4-Methyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzaldehyde-160 [11] To a Schlenk tube were added bis(pinacolato)diboron (1.22 g, 4.8 mmol, 1.2 eq.), 2-bromo-4-methylbenzaldehyde (0.80 g, 1.0 eq.), PdCl2(dppf) (88 mg, 3 mol %) and KOAc (1.18 g, 3.0 eq.).

The mixture was closed by a septum, purged with argon several times then dry 1,4-dioxane (15 mL) was then added into the reaction mixture was kept stirring at 80 °C for 36 h. The crude reaction mixture was diluted with dichloromethane and washed by NaHCO3. The combined organic layers were collected, dried over the MgSO4, and concentrated in vacuo. The residue was purified through flash silica gel plug (n-heptane/EtOAc, 9:1 as eluent) to give 0.98 g (>99% yield) of 160 as colorless oil.

1 H-NMR (400 MHz, CDCl3 H 1 ), 7.70 (d, 3 J = 7.9 Hz, 1H 6 ), 7.52 (d, 5 J = 1.9 Hz, 1H 3 ), 7.17 (dd, 3 J = 8.0, 5 J = 1.8 Hz, 1H 5 ), 2.24 (s, 3H 4 ), 1.24 (s, 12H 2B ). NMR analysis of 173 was in accordance with literature. [11] 2-(6-Methoxy-9-methyl-9H-carbazol-3-yl)-4-methylbenzaldehyde-153b

In a pre-dried Schlenk, 136 (0.200 g, 0.59 mmol), 160 (0.177 g, 6 eq.), and K2CO3 (0.25 g, 3 eq.) were dissolved in a mixture of DMF (36 mL) and water (12 mL). The mixture was degassed by argon bubbling for 15 minutes before Pd(PPh3)4 (34 mg, 3 mol%) was added and the resulting solution refluxed for 16 hours. After cooling down to room temperature, the reaction was poured into 20 mL of water and the organic layer was extracted 3 times with ethyl acetate (3*20 mL) and thus washed with brine (20 mL) and dried over anhydrous MgSO4. Solvents were removed under vacuum and the product was purified by silica gel chromatography (n-heptane/CH2Cl2, 9:1 as eluent) to give 100 mg (51% yield) of 153b as a white solid. The compound is used without further purification. (-)-155b: = +1550 ± 1%, = +6680 (c = 1.6 10 -3 , CH2Cl2).

4,4'-Dimethyl-2-nitro-1,1'-biphenyl-166 [12] A suspension of 4,4 -dimethylbiphenyl (1.00 g, 5.50 mmol) in Ac2O (30 mL) was immersed in a room-temperature water bath. A mixture of HOAc (1.50 mL) and fuming HNO3 (0.90 mL) was added rapidly, dropwise. TLC indicated that the reaction was complete within 10 min. The mixture was poured into H2O (200 mL), stirred only for a few minutes, and extracted with CH2Cl2 (3 × 20 mL). The combined organic layers were washed with 1 M NaOH (2 × 20 mL) and brine, dried over MgSO4, and concentrated; a large volume remained (probably Ac2O that had not hydrolyzed). The solution was then taken up in H2O (400 mL), treated with NaOH (approximately 2 g), and stirred for approximately 30 minutes during which time a yellow precipitate developed. The mixture was extracted with Et2O (3 × 25 mL), and the combined layers were washed with saturated NaHCO3 (75 mL) and brine, dried over anhydrous MgSO4, and evaporated under reduced pressure. The crude product was purified by silica gel chromatography (n-heptane/CH2Cl2, 8:2 as eluent) gave the desired product as a pale-yellow solid.

1 H-NMR (300 MHz, CDCl3) 7.67 (m, 1H 3 ), 7.45 (ddd, 3 J = 7.9, 5 J = 1.8, 0.8 Hz, 1H 5 ), 7.37 (d, 3 J = 7.9 Hz, 1H 6 ), 7.29 (s, 4H ), 2.50 (d, 5 J = 0.8 Hz, 3H 4 ), 2.46 (s, 3H ). NMR analysis of 166 was in accordance with literature. [13] 2,7-Dimethyl-9H-carbazole-167 [12] A solution of 4,4'-dimethyl-2-nitro-1,1'-biphenyl (350 mg, 1.54 mmol) and PPh3 (1.00 g, 2.5 eq.) in o-dichlorobenzene (3.5 mL) was heated to reflux with vigorous stirring for 21 h, during which time the color changed from yellow to brown. After 16 h, the solvent was stripped under a high vacuum and the resulting dark orange semisolid slurred in heptane (5 mL) to precipitate the PPh3O, which was removed by filtration, and then purified by silica gel chromatography (heptane/CH2Cl2, 100:0 75:25) gave 180 mg (60%) of 167 as an off-white solid. ). NMR analysis of 167 was in accordance with literature. [14] 2,7,9-trimethyl-9H-carbazole-168 2,7-Dimethyl-9H-carbazole 167 (150 mg, 0.77 mmol) was dissolved in 5 mL of N,Ndimethylformamide under inert atmosphere. Sodium hydride (70 mg, 2.5 eq.) was then added, and the solution was stirred for 5 minutes at room temperature. Then, 150 L of methyl iodide (3 eq.)

were added and continued stirring for 1 h. The subsequent reaction mixture was poured into 100 mL water, extracted with dichloromethane (2 x 10 mL), and washed with water (2 x 10 mL) and brine (1 x 10 mL). The organic phase was dried over anhydrous MgSO4, and the solvents evaporated under reduced pressure. The crude product was passed through a short silica plug (nheptane/CH2Cl2, 9:1 as eluent) to yield 150 mg (94%) of 168 as a white solid. ). NMR analysis of 168 was in accordance with literature. [15] 3,6-Dibromo-2,7,9-trimethyl-9H-carbazole-169 270 mg (2.0 eq.) of N-bromosuccinimide were added to a solution of 150 mg (0.71 mmol) 2,7,9-trimethyl-9H-carbazole 168 in 20 mL of tetrahydrofuran (THF) at room temperature. Then, the mixture was stirred for 5 h at room temperature. Then, the resulting mixture was poured into water and extracted with CH2Cl2 (3 × 10 mL). The combined organic phases were washed with NaHCO3 and brine, dried over anhydrous MgSO4 and evaporated under reduced pressure.

The crude product was filtered over a silica plug (n-heptane/CH2Cl2, 9:1 as eluent) and used without further purification. 173 [10] To a solution of compound

Experimental optical rotation values

(+)-172: = 3000 ± 1%, = 19500 (c = 1.0 10 -3 , CH2Cl2).

( )-172: = +3000 ± 1%, = +19500 (c = 1.0 10 -3 , CH2Cl2).

Compound 173:

1 H-NMR (400 MHz, CD2Cl2) H 3 ), 7.43 (d, 5 J = 2.0 Hz, 1H

Experimental optical rotation values

(+)-173: = 900 ± 3%, = 5800 (c = 1.0 10 -3 , CH2Cl2).

( )-173: = +850 ± 4%, = +5500 (c = 1.0 10 -3 , CH2Cl2). L, every 8.5 minutes. ee > 94.5%

HR-MS

Résumé en français Chapitre 1 Introduction : La chiralité et les radicaux

Les matériaux -conjugués chiraux ont récemment émergé comme une voie prometteuse en science de matériaux en raison de leurs interactions spécifiques avec une lumière circulairement polarisée (CP en anglais), et du potentiel de cette dernière dans plusieurs domaines d'applications tels que les diodes organiques électroluminescentes (OLEDs en anglais), les transistors organiques à effet de champ (OFETs en anglais) ou tes chiraux. [1] Alors que des recherches approfondies se sont concentrées sur les colorants chiraux organiques avec une configuration électronique à couche fermée, attention a été accordée à leurs homologues à couche ouverte (les radicaux), vraisemblablement en raison de leurs problèmes de réactivité et de stabilité configurationnelle. Les radicaux chiraux possèdent chiralité et le spin. Bien que les radicaux chiraux intrinsèques aient été étudiés sur longue période, l'isolement de radicaux persistants est resté difficile, avec uniquement quelques exemples au cours de la dernière décennie (Figure F-2). En termes de propriétés chiroptiques, les systèmes hélicoïdaux peuvent fournir une réponse intense en dichroïsme circulaire électronique (ECD en anglais), par rapport à d'autres types de chiralité. Cependant, en termes de luminescence, ce n'est que dernièrement que la chiralité de l'hélice a présenté cette propriété dans le cas des systèmes triarylméthyle. Les radicaux chiraux avec deux spins ou plus sont encore plus exceptionnels, difficiles à obtenir, et limités à quelques systèmes seulement. Comme mentionné cidessus, les principales stratégies de stabilisation radicalaire ont été utilisées et combinées avec la stabilisation de la chiralité, qui a montré des propriétés et un potentiel unique vers les systèmes à haut spin principalement par l'extension de la -conjugaison. [2-6] Par conséquent, cette thèse vise le développement de nouveaux radicaux chiraux intrinsèques à base de carbazole étude de leurs propriétés photophysiques, chiroptiques et magnétiques, et à rationaliser le mécanisme de formation de ces radicaux via un processus d'inversion de niveau SOMO-HOMO peu commun à l'état mono-et di-radicalaire, qui er la stabilité de ces radicaux. En général, la plupart des radicaux ont une configuration électronique commune, où l'orbitale moléculaire individuellement occupée (SOMO) est l'orbitale occupée la plus haute en énergie. Néanmoins, certains radicaux organiques ne suivent pas cette règle, conduisant à une configuration électronique particulière à savoir l'inversion des niveaux SOMO-HOMO (SHI en anglais, Figure F-3). [7][8] La configuration électronique SHI est généralement confirmée par des calculs théoriques, associés à quelques expériences, comme par exemple l'électrochimie et la formation des polyradicaux correspondants. Le SHI dans les radicaux organiques a été observé depuis plusieurs décennies dans une large gamme de composés tels que les donneurs polarisés en spin (spin-polarized donors en anglais) [9][10] , les complexes organométalliques [11] et les radicaux ioniques perturbés. [12] Cependant, la compréhension et les effets du SHI sont encore peu rationalisés et il n'y a pas de critères généraux pour obtenir l'interaction électronique entre les orbitales moléculaires frontières d'une molécule à l'autre.

En outre, le SHI est apparu comme un nouveau facteur qui peut contribuer à la stabilisation chimique écule radicalair encombrants et à la délocalisation de spin sur les systèmes moléculaires -conjuguées.

nous nous sommes demandés ent être combinées avec propriété de de ce nouvelle entité, puisque ces questions entravent actuellement le domaine de la recherche sur les systèmes chiraux moléculaires à couche ouverte. [13] Nous avons ainsi porté notre attention sur le système C2-bicarbazole, un analogue de BINOL nommé BICOL (Figure F-4a). Ces dérivés ont suscité un intérêt grâce à leurs nombreuses possibilités , en biologie, [14][15] en reconnaissance chirale, [16] ainsi qu synthèse asymétrique. La différence de leurs propriétés redox nous a permis ensuite d'étudier la formation de nouveaux cations monoradicaux organiques chiraux persistants à base de bicarbazole. Une stabilité particulière, dépendante du type de chiralité, a été observée pour le radical bicarbazole axial non protégé, et non pour le monocarbazole 128b ni pour le bicarbazole hélicoïdal 129. Ces résultats ont été expérimentalement et théoriquement rationalisés, révélant la formation de SHI dans les monoradicaux bicarbazoles axiaux et du couplage électronique entre les deux unités de carbazole, modulé par leur angle dièdre respectif. Ces différents facteurs apparaissent comme étant co-responsables de la stabilité sans précédent du monoradical axial. Ces résultats nous ont permis d'explorer en profondeur le SHI dans les radicaux organiques chiraux, apportant de nouvelles informations concernant son impact sur la stabilité de ces radicaux (Figure F-6). Les diradicaux correspondants ont également montré des réponses ECD dans le PIR jusqu'à 1100 nm et les états singulet-triplet se sont révélés quasi-dégénérés avec de faibles interactions antiferromagnétiques évaluées par résonance paramagnétique électronique à température variable (VT-EPR en anglais). Les calculs théoriques ont montré que la configuration SHI dans les systèmes mono-et diradicalaires est également co-responsable de leur stabilité. À notre connaissance, ils représentent les premiers exemples de diradicaux avec SHI.

Chapitre 4 -Diradicaux chiraux diindénocarbazoles avec SHI : une direction possible vers des triradicaux chiraux stables

Dans le dernier chapitre, nous avons appliqué la stratégie décrite précédemment pour la synthèse de radicaux organiques chiraux avec une configuration électronique SHI. ces dernières centrés sur un atome de carbone ont suscité un vif intérêt en raison de leur nature trivalente qui permettent une diversité moléculaire. Cependant, ils sont souvent moins stables en raison de leur réactivité avec l'oxygène atmosphérique et de leur forte capacité à former des liaisons carbone-carbone. [21] À cet effet, nous visons à stabiliser les radicaux centrés sur le carbone en utilisant le SHI. L'un des radicaux centrés sur le carbone le plus intéressant est le radical fluorényle, un analogue carboné du carbazole (Figure F-14). Notre approche consiste à créer une unité indènyle connectée au squelette du carbazole, à savoir l'indénocarbazole, dont un seul dérivé d'indénocarbazole a été rapporté dans une publication sous la forme de polyradicaloïdes.

Conclusion et perspectives

En conclusion, dans le cadre de cette thèse, des molécules chirales à base de carbazole ont été préparées. Nous avons étudié leurs propriétés photophysiques, chiroptiques et électrochimiques à la fois en couche fermée (l'état neutre) et en couche ouverte (mono-et di-radicaux). Ils ont montré une stabilité sans précédent et des propriétés électroniques et magnétiques uniques à la fois en solution et à l'état solide. Cette stabilité unique a été rationalisée notamment pour l'inversion de niveau SOMO-HOMO (SHI) et la distribution des spins dans l'ensemble du système.

En raison de la stabilité des radicaux obtenue, nous pouvons utilisation de ces systèmes moléculaires dans plusieurs applications prometteuses telles que la préparation d OLEDs et OFETs. Il est également possible d'ajouter une unité d'ancrage à ce type de système et de l'immobiliser sur la surface d une électrode pour étudier leur spintronique et effet CISS.

Figure A .

 A Figure A. Structure of bicarbazoles and tetracarbazoles studied in this manuscript.

Figure B .

 B Figure B. Structure of indenocarbazoles studied in this manuscript.

Figure 1 - 1 .

 11 Figure 1-1. Human hands as chiral objects. Figure was reproduced from ref 2.

Figure 1 - 2 .

 12 Figure 1-2. Different types of chirality. Figure was adapted from ref 2.

Figure 1 - 3 .

 13 Figure 1-3. Chemical structure and enantiomer of thalidomide.

Figure 1 - 4 .

 14 Figure 1-4. Left and right CP-light. Figure was modified from ref 11.

Figure 1 - 5 .

 15 Figure 1-5. Top: Illustration of electronic circular dichroism (ECD, left) and circularly polarized luminescence (CPL, topright) principle with dissymmetric factors and , which refer to absorption and emission involvement. The quantities of , , , and represent the molar extinction coefficients and emission intensities for left-CP and right-CP. Figure was modified from ref 11. Bottom: Chemical structures and ECD spectra of carbo[6]helicene (H6 -binaphthol (BINOL, right) in dichloromethane.

Figure 1 - 6 .

 16 Figure 1-6. a) Illustration of the benefits of using anti-glare filters. b) Example of CP-luminescence compound base on helical chirality (1-2) and axial chirality (3-4). c) Circularly polarized luminescence (CPL) spectra of 2a and 2b in dichloromethane. d) Corresponding plots of the luminescence (from the vapor deposition film) and electroluminescence dissymmetry factors, glum and gEL, of CP-OLED devices based on compound 2b respectively. Figure was modified according

  Figure was modified according to ref 11 and 17.

Figure 1 - 7 .

 17 Figure 1-7. An iron alkynyl helicene 5 for NIR chiroptical switching. Figure was modified according to ref 22.

Figure 1 - 8 .

 18 Figure 1-8. a) Schematic represents the conditions needed to observe a MChD signal on a chiral molecule. b) Helicenebased Yb complex 6 MChD. Figures were reproduced according to ref 24 and 26.

Figure 1 - 9 .

 19 Figure 1-9. a) A scheme describing the charge and spin polarization in two enantiomers of a chiral molecule when an electric field (black arrow) is applied. The red balls indicate the electrons with their spins (small vertical black arrows) and the angular momentum of the spin is presented by the blue horizontal arrows. b) Scheme representing a spin-selective formation of 3 O2 (spin aligned) and 1 O2 (spin antiparallel). c) Chiral and achiral Zn porphyrins 7a and 7b used as photosensitizers and their supramolecular aggregation. d) Schematic represents how spin filtrating works in chiral molecular systems preventing hydrogen peroxide recombination process. e) The current density as a function of the potential in photoelectrochemical cell coated with self-assembly chiral and achiral Zn-porphyrin 7a and 7b. Figures were reproduced according to ref 35 and 40.

Figure 1 - 10 .

 110 Figure 1-10. Common monoradical analogs.

Figure 1 - 11 .

 111 Figure 1-11. Left: Open shell electronic structure. Right: Zeeman effect on the unpaired electrons in the applied magnetic field and EPR spectrum for the simplest system. Figure was reproduced from ref 48.

Figure 1 - 12 .

 112 Figure 1-12. Left: Comparison between monoradical, biradical, and diradical in EPR response. Right: Scheme represents diradical character in terms of spin and correspondent spin multiplicity. Figure was reproduced from ref 48.

- 12 ,

 12 left-middle). Diradicals can be characterized by the appearance of two spin states under the magnetic field, namely singlet (S = 0) and triplet (S = 1), Figure 1-12, right. Singlet diradicals are EPRsilent because the total spin multiplicity (2S+1 = 1) resulted in only one energy level in the magnetic field. On the other hand, triplet diradicals (spin multiplicity = 2S+1 =3) are EPR active. Diradical characters are highly dependent on the distance between the two radical centers, which can be observed by EPR analysis. In the simplest case, as depicted in Figure 1-12 (bottom), when the two aminoxyl groups are close enough, the three hyperfine signals were derived to a five-line signal together with possible forbidden transition ( ms = 2, Figure 1-13, noted as 3).

Figure 1 - 13 .

 113 Figure 1-13. Zeeman effect on the two unpaired electrons in the applied magnetic field and EPR spectrum for the diradical s = ±2) at half field.Figure was modified according to ref 48.

  Figure was modified according to ref 48.

Figure 1 - 14 .

 114 Figure 1-14. Schematic illustration of the possible electronic configurations of diradical.Figure was modified according to ref 43.

Figure 1 - 15 .

 115 Figure 1-15. Left: Simple IT vs T plot from EPR spectra for singlet (dot line), double (solid line), and triplet (dash-dot

1- 16 .

 16 Compared to paramagnetic material, ferromagnetic and antiferromagnetic interactions express a downward and upward deviation, respectively. The Curie Weiss law successfully explains such deviation by introducing the Weiss constant ( ) (equation9). The Weiss constant value has a direct relation to the magnetic behavior of the molecule, in which > 0 is the ferromagnetic system and < 0 is the antiferromagnetic system.

Figure 1 - 16 .

 116 Figure 1-16. The relationship between the inverse molar magnetic susceptibility ( m 1 ) and temperature.Figure was modified according to ref 52.

Figure 1 - 19 .

 119 Figure 1-19. Polychlorinated triphenylmethyl radicals 12-13.

Figure 1 - 20 .

 120 Figure 1-20. Phenylenyl radical and its resonance structure.

Figure 1 - 21 .

 121 Figure 1-21. Compound 14 with imidazolium stabilizer and tetrathiafulvalene radical cation 15.

Figure 1 - 22 .

 122 Figure 1-22. Organic with ferromagnetic interaction 16. The figure was reproduced according to ref. 78.

Figure 1 - 24 .

 124 Figure 1-24. Molecular structure of dithiadiazolyl radical 21. The figure was reproduced according to ref. 83.

Figure 1 - 25 .

 125 Figure 1-25. Galvinoxyl radical 22 and spin-polarized donors based on TTF, ESBN 23-25.

Figure 1 -

 1 Figure 1-26. a) Schematic of spin-polarized donor system 24 upon one-electron redox process at the donor fraction. b) Magnetic field dependence of magnetoresistance of 242ClO4 at various temperatures at a bias voltage of 7 V. c) Plausible spin-dependent electron transfer in the 24/24 + dimer. d) magnetization (M)-applied field (H) curves of 242ClO4 at 2 K. e) Magnetoresistance in an applied magnetic field at 2 K with a bias voltage at 10 V.Figure was reproduced according to ref 103.

Figure 1 - 27 .

 127 Figure 1-27. Top: Triphenylmethyl-based luminescence radical 26-28. Bottom: EQE of compounds 27 and 28, reproduced from ref 113 and 116.

Figure 1 - 28 .

 128 Figure 1-28. Left: Organic radical for OFETs 29-30. Right: Hole-drift mobility of compound 29 in white circles, reproduced from ref 119.

Figure 1 -

 1 Figure 1-29. a) Organic diradicaloid for OFETs 31-32. b) Photograph of the OFET 31. c) Schematic drawing of a bottomcontact bottom-gate OFET with a single crystal of 31, reproduced from ref 120.

Figure 1 - 30 .

 130 Figure 1-30. Schematic presents how 21 acts as a spin-flip center at the interface of a heterojunction organic solar cell. The dashed circles indicate the charge transfer states at the donor-acceptor interface. The red species is the electron-donating material, and the blue species is the electron-accepting material.Figure was reproduced according to ref 122.

Figure 1 - 26 .

 126 Figure 1-26. Left: Diradical 33. Right: Infrared thermal images of 33 powder under an 808 nm laser irradiation (0.8 W/cm 3 ) at different irradiated times. Figure was reproduced from reference 127.

1 - 29 .

 129 Figure 1-29. Molecular structure of chiral PROXYLs and DOXYLs 40-43.

Figure 1 - 30 .

 130 Figure 1-30. Chiral BEDT-TTF 44-45 and EDT-TTF 46.

Figure 1 - 31 .

 131 Figure 1-31. Example of TTF derivative with chiral methyl-oxazoline BEDT-TTF 47-chiral bis(pyrrole) derivatives 48 and chiral sulfoxide derivatives 49.

Figure 1 -

 1 Figure 1-32. a) Example of chiral TTF derivative with binaphthyl 50-51 and allene 52. b) ECD spectra of (S)-52 2+ (dashed red line), (S)-52 4+ (solid red line), (R)-52 2+ (dashed blue line), and (R)-52 4+ (solid blue line) in DCM MeCN (v/v = 4:1) solution.Figure was adapted according to ref 166.

  Figure was adapted according to ref 166.

Figure 1 -

 1 Figure 1-33. a) Example of chiral TTF derivative with planar chirality 53-54. b) ECD spectra of (R)-53 2+ (black) and (S)-53 2+ (gray) in CH2Cl2-MeCN solution and electronic absorption spectra of 53 2+ (bottom) in the same conditions. c) ECD spectra of (R)-53 4+ (black) and (S)-53 4+ (gray) and electronic absorption spectra of 53 4+ (bottom) in the same conditions.Figure was reproduced according to ref 167.

  Figure was reproduced according to ref 167.

Figure 1 -

 1 Figure 1-34. a) Stable triphenylmethyl-based radical series with propeller chirality 12-13, 55-59. EPR spectra of 56-C2 (b) and 56-D3 (c) in glassy toluene at 143 K.Figure was reproduced according to ref. 171.

  Figure was reproduced according to ref. 171.

-

  14 and -45 M -1 cm -1 , respectively). Compounds 12 and 13 are emissive and displayed a weak CPL signal centered at 569 and 605 nm with factors of 5 and 8 × 10 -4 for 12 and 13 respectively (Figure 1-35).

Figure 1 - 35 .

 135 Figure 1-35. ECD (top) and CPL (bottom) of TTM 12 (left) and PTM 13 (right) radical.[173] Figure was modified according to ref 173.

Figure 1 - 36 .

 136 Figure 1-36. Chemical structure of helicene radical anions 60-61 and helical binaphthyl nitroxide 62.

Figure 1 - 37 .

 137 Figure 1-37. Chemical structure of compound 63 and ECD spectra formed in the reaction of (M)-63 with [NO][PF 6 ] in dichloromethane. The ECD spectra were modified according to ref 183.

Figure 1 -

 1 Figure 1-38. a) Structure of helical chiral radical 64-66.[184][185][186] b) ECD spectra and chiroptical switching in acetonitrile.

  Figure was reproduced according to ref 186.

Figure 1 - 39 .

 139 Figure 1-39. Structure of helical chiral radical 67 (a) and 68 (c). b) EPR spectrum of 67 (g = 2.0038) in CH2Cl2 at 298 K. d) Structure of helical chiral radical 69 and generation of neutral 69 and radical cation 69 . EPR spectrum was reproduced according to ref 187.

Figure 1 - 40 .

 140 Figure 1-40. Structure of helical chiral radical 70-74. Top right: ORTEP drawings (thermal ellipsoids at 50% probability) of 70 hydrogens are omitted for clarity.Figure was reproduced according to ref 190.

  Figure was reproduced according to ref 190.

Figure 1 - 41 .

 141 Figure 1-41. Left: Twistacenes based radical 75-83. Right: ECD spectra of M and P enantiomers (solid and dashed lines, respectively) of 80-83 (red) and 80 -83 (blue) in acetonitrile.Figure was reproduced according to ref 196.

Figure 1 -

 1 Figure 1-42. a) Molecular structure of chiral diradicals 84-86. b) CD spectra of (Ra)-and (Sa)-85 •2[SbCl6 ] in CH2Cl2. c) Quantitative EPR spectroscopy of 0.82 mM diradical dication 86 •2[SbF6 ] in DBP. Figure was reproduced according to ref 198-199.

Figure 1 - 43 .

 143 Figure 1-43. Left: Molecular structure of cethrene derivatives 87 and 88. Right. ECD spectra of the enantiomers of c-88a (red), separated by HPLC employing a chiral stationary phase, and o-88 (blue), generated from the c-88a upon irradiation (365 nm, 1 min). The spectra of toluene samples were recorded at 283 K, and the absolute configurations were assigned with the aid of TD-DFT calculations (vertical lines). The ECD spectra were modified according to ref 189.

Figure 1 - 44 .

 144 Figure 1-44. Structure of diradicaloid picene 89. Right: ECD spectra of 89b in CHCl3. Figure was reproduced according

  Figure 1-44. Structure of diradicaloid picene 89. Right: ECD spectra of 89b in CHCl3.Figure was reproduced according to ref 201.

Figure 2 - 1 .

 21 Figure 2-1. Schematic comparison between the electronic configuration found in classical radicals and the organic radicals presenting SOMO-HOMO inversion (SHI). The figure was modified according to ref 5.

Figure 2 - 2 .Figure 2 - 3 .

 2223 Figure 2-2. Galvinoxyl radical 22 and its orbital energies configuration.

2 - 4 .

 24 Figure 2-4. a) Schematic illustration of the spin-polarized donor structures with corresponding torsion angle between the radical and donor fragments. b) Nitronyl nitroxide radical 91c, 91l, and 91m. Degrees mentioned in 91c and 91m display a torsion angle between the donor and radical fragments. c) Electronic structure of (A) classic radical and (B, C) spinpolarized donor radicals. The curved arrow represents an electron removed by one-electron oxidation. The figure was modified from ref 28.

Figure 2 - 5 .

 25 Figure 2-5. Electron delocalization of m-xylylene diradical and p-xylylene diradicaloid represents non-disjoint and disjoint SOMOs, respectively, notion by Borden and Davidson.

Figure 2 - 6 .

 26 Figure 2-6. Examples of spin-polarized donors reported in the last 20 years.

Figure 2 - 7 .

 27 Figure 2-7. a) Tempodt 92a, platinum-tempodt complex 92, and dimerized complex. b) UV-vis spectra of 92 and 922 2+ . c) EPR spectrum of 922 2+ . The figure was modified according to ref 46.

Figure 2 - 8 .

 28 Figure 2-8. Examples of radical-metal complexes with SHI.

2- 9 )

 9 and discussed the electronic configuration of the latter molecule either in the protonated or non-protonated form of the acidic group. While 95 exhibited SHI, its protonated species restored the usual molecular orbital configuration (non-SHI), 96, representing an unprecedented possibility to switch between SHI and non-SHI configuration associated with pH or other cations. Further theoretical and experimental experiments showed that the SHI configuration contributes to increase the stability of the radical species, opening an interesting approach to study for less stable radicals, based for instance on carbon derivatives.

Figure 2 - 9 .

 29 Figure 2-9. Molecular orbital configurations of the carboxy-aminoxyl in both anion radical (95) and neutral radical (96) forms. The figure was modified according to reference 50.

Figure 2 - 10 .

 210 Figure 2-10. Azathia[7]helicene 75 and its analogs 75a, thia[7]helicene 69, and oxathia[7]helicene 97.

Figure 2 -

 2 Figure 2-11. a) DFT-optimized structure of the 75. b,c) Orbital energies (in eV) and isosurfaces (±0.030 a.u.) of the selected MOs for the neutral closed-shell neutral (b) and the corresponding radical cation (c) for the N-protonated form of ATH, respectively. The figure was reproduced from ref. 5.

2 - 12 .

 212 Figure 2-12. Examples of organic ion-radicals with SHI electronic configuration.

Figure 2 - 13 .

 213 Figure 2-13. Compounds 106 and 107 where the red color represents the spin density of the corresponding radical species.

Figure 2 - 14 .

 214 Figure 2-14. Top: Polychlorophenylmethayl radical based donor-radical systems 28, 108, and 109.

Figure 2 - 15 .

 215 Figure 2-15. Energies and wave functions for the frontier molecular orbitals of 28 (a), 108 (b), and 109 (c). The figure was reproduced according to ref 12.

Figure 2 - 16 .

 216 Figure 2-16. Cyclicvoltammograms of compounds 108 (left), 28 (middle), and 109 (right) with a comparison between each fraction of the molecules. The figure was modified according to reference 12.

Figure 2 - 17 .

 217 Figure 2-17. BINOL, BIFOL and BICOL analogues.

  -17).BICOL is the C2-biaryl system class composed of two carbazole units, linked in their 4--positions. This compound is easily functionalized thanks to the presence of an amino group at 9-position, which allows chemists to tune their properties by either pre-or post-functionalization reactions. Several C2-bicarbazole systems can be considered depending on a link between the two carbazole units (Figure2-18 B ICOL most common pattern by means of BINOL -connection.

Figure 2 - 18 .

 218 Figure 2-18. Top: Carbazole numbering system. Bottom: Example of bicarbazole-diol isomers, the numbering of position entire the molecule can be count from each carbazole unit with hydroxy-prioritized.

Figure 2 - 19 .

 219 Figure 2-19. Enantiomers of BICOL and enantiomeric identification based on the CIP rule.

Figure 2 -

 2 Figure 2-20. a) Illustration of exciton coupling phenomenon. b) (S)-1,19-binaphthalene structure. c) Calculated CD spectra as a function of the dihedral angle of (S)-1,19-binaphthalene structure. d) Experimental spectra of two compounds demonstrating the same effect (calculated dihedrals 55 for blue structure, solid line, and 90 ; for red structure, dotted line). e) Definition of exciton chirality and theoretical excitonic coupling signature in ECD. The figure was reproduced according to ref 77.

Figure 2 - 21 .

 221 Figure 2-21. ECD spectra of (R)-BICOL (red) and (S)-BICOL (blue). The ECD was recorded according to ref 82 and the absolute configuration realized by ref 83.

Figure 2 - 22 .

 222 Figure 2-22. Natural BICOL derivatives.

Figure 2 - 23 .

 223 Figure 2-23. Left: chiral recognition observed by ECD of b-DNA interacted with BICOL. The figure was reproduced from ref 82. Right. BICOL derivatives 112-113 as a ligand for asymmetric hydrogenation.

position 2 using 2 - 1 .

 221 Scheme 2-1. Synthesis towards bicarbazole 1102 and 1112.

Figure 2 -

 2 Figure 2-24. X-ray structure of a) BICOL, b) 128, and c) 129 with the corresponding dihedral angle between the carbazole units. Hydrogen atoms are omitted for clarity reasons and optimized structures of carbazole compounds d) 128 and e) 129.

Figure 2 -

 2 Figure 2-25. 1 H NMR spectra of compound 128 (in CD2Cl2) and 129 (in CDCl3) in aromatic region (400 MHz, 298 K).

Figure 2 -

 2 Figure 2-26. X-ray structure of 130 (a, two molecules within the same unit cell) and 131 (b) with the corresponding dihedral angle between the carbazole units. Hydrogen atoms are omitted for clarity. c) Conformers of 130 with a different dihedral angle; 65.5 (blue) and 106.6 (red).

Figure 2 -

 2 Figure 2-27. 1 H NMR spectra of compounds 130 and 131 (CD2Cl2, 400 MHz, 298 K).

bicarbazoles 128 -

 128 131 have been measured in dichloromethane with concentrations in the range of 10 -5 -1 , and rationalized by (TD)-DFT calculations for bicarbazoles 128-130 performed by Dr. Laura Abella and Pr. Jochen Autschbach, University at Buffalo, State University of New York, USA).

Figure 2 - 28 .

 228 Figure 2-28. Chemical structure of carbazoles 128b and 130b and bicarbazoles 128-131.

Figure 2 - 29 .

 229 Figure 2-29. UV-vis spectra of compound 128 (black), 129 (red), 130 (green), 131 (blue), 128b (violet) and 130b (orange) in dichloromethane (ca. 10 -5 M) at 298 K. Inset a) UV-vis spectra of 128 and 128b b) UV-vis spectra of 128 and 129 in the same condition as the main figure.

Figure 2 - 30 .

 230 Figure 2-30. Left: Isosurfaces (±0.030 a.u.) of HOMO-1, HOMO, and LUMO for 128 and 129. Right: Calculated (Calc.) absorption spectra for (+)-128 (black) and (+)-129 (red). Selected transitions and oscillator strengths are Tables 2-3 and 2-4.

2 Figure 2 - 31 .

 2231 Figure 2-31. ECD spectra of compound (+)-128 (black), (+)-129 (red), (+)-130 (green) and (+)-131 (blue) in dichloromethane (ca. 10 -5 M) at 298 K. Corresponding (-)-enantiomers are represented in grey lines.

Figure 2 - 32 .

 232 Figure 2-32. Left: Experimental (Expt.) electronic circular dichroism (ECD) spectra for (+)-128 (solid black line) and (+)-129 (solid red line) in DCM. Right: Calculated (Calc.) ECD spectra for (+)-128 (solid black line) and (+)-129 (solid red line). Corresponding (-)-enantiomers are represented in dashed lines. Selected transitions and rotatory strengths are indicated

Figure 2 - 33 .

 233 Figure 2-33. Experimental (Expt.) ECD spectra of (+)-130 and Calculated (Calc.) ECD spectra for the two different conformers of (+)-130. The conformer with a dihedral angle of 106 is plotted in purple, while the other conformer (65°) appears in black.

Figure 2 - 34 ,

 234 left. Bicarbazoles 128 and 129 display moderately intense fluorescence around 400 nm, with photoluminescence quantum yields in the range of 20% (Figure 2-34 and Table2-6).The greater electronic communication between the two carbazole units in 129, observed when comparing the UV-vis absorption spectra of the latter with compound 128, also remains present in the excited state as indicated by the red-shifted 20 nm of its emission peak, in comparison to the emission band of 128, found at 405 nm. In fact, the emission profile of 128 appears very close to the one recorded for carbazole 128b, confirming that the electronic coupling between the carbazole -systems also remains weak in the excited state of 128. The influence of the tert-butyl group in 130, 131, and 130b is also limited in the excited state with a slight red-shift of 5 nm observed in their corresponding maximum emission peaks comparing to their non-functionalized analogs.

Figure 2 - 34 .

 234 Figure 2-34. Left: Fluorescence spectra of compound 128 (black), 129 (red), 130 (green), 131 (blue), 128b (violet) and 130b (orange) in dichloromethane (ca. 10 -5 M) at 298 K. Right: Calculated emission spectra of 128 (black) and 129 (red) using the first electronic transition in the excited state optimization in gas phase. The intensities are plotted based on Gaussian broadening with . Corresponding experimental data is indicated in dashed lines.

Figure 2 -

 2 35 (right, vide infra), and normalized to 2 on the maximum of their corresponding photoluminescence spectra to allow a direct lecture of the glum factor at this emission wavelength. Each pair of enantiomer gave mirror-image CPL spectra, enabling us to determine promising glum factors of 0.6, 1.5, 0.6, and 1.3 10 -3 for 128-131,

3 IFigure 2 - 35 .

 3235 Figure 2-35. Left: gabs spectra. Right: CPL spectra of compounds (+)-128 (black), (+)-129 (red), (+)-130 (green), and (+)-131 (blue) in dichloromethane (ca. 10 -5 M) at 298 K. Corresponding (-)-enantiomers are represented in dashed lines.

Figure 2 -

 2 Figure 2-36 and Table 2-7), compounds 128 and 130b display a first reversible oxidation event

Figure 2 - 36 .Scheme 2 - 10 . 2 . 9 Scheme 2 - 11 .

 23621029211 Figure 2-36. Cyclic voltammograms of 128 (black), 129 (red), 128b (purple), and 131b (orange) versus saturated calomel electrode (SCE) as the reference and 0.2 M Bu4NPF6 in dichloromethane with ferrocene as internal standard.

Figure 2 - 37 .

 237 Figure 2-37. Left: UV-vis-NIR absorption spectra of 130b (black) and 130b + BF4 -(red). Middle: UV-vis-NIR absorption spectra of 128 (black) and 128 + BF4 -(red). Right: UV-vis-NIR absorption spectra of 129 (black) and 129n + BF4 -(red).

129 Figure 2 - 38 .

 129238 Figure 2-38. UV-vis titration studies of 128 (left) and 129 (right) by magic blue in dichloromethane (c = 7 × 10 -5 M) at 298 K.

130b + -Air c Figure 2 - 39 .Figure 2 -

 c2392 Figure 2-39. UV-vis-NIR absorption spectra of 128 + in dichloromethane at 298 K under argon atmosphere (a) and air atmosphere (b) and 130b + in dichloromethane at 298 K under air atmosphere (c).

Figure 2 -

 2 Figure 2-41a. LRMS spectrum (dithranol, dichloromethane) of the sample obtained after a reduction of monoradical cation 128 under argon atmosphere. The spectrum suggests that an oligomerization process occurred as one of the degradation pathways of 128 .

Figure 2 -

 2 Figure 2-41b. LRMS spectrum (dithranol, dichloromethane) of the sample obtained after a reduction of monoradical cation 128 under air atmosphere. The spectrum suggests that an oligomerization process occurred as one of the degradation pathways of 128 .

Figure 2 -

 2 Figure 2-42. a) EPR spectra of monoradical (128 (black) and 130b (orange)) with AgBF4 in dichloromethane at 298 K. b) Simulated EPR spectra of 128 suggesting the presence of organic radical with ½ spin. g refers to g-value of the free electron, lineshape refers to a value of Lorentzian content of line, and simple LW refers to a value of the constant spectral linewidth in Gauss.

3 in 1 , 2 -Figure 2 - 43 .

 312243 Figure 2-43. Experimental (left, Expt.) and calculated (right, Calc.) ECD spectra of (+)-128 (black) and (+)-128 + BF4 - (red) with their corresponding enantiomers marked with a dashed line in dichloromethane at 298 K with an experimental extension of the NIR-ECD spectra of (+)-and (-)-128 + BF4 -.

Figure 2 - 44 .

 244 Figure 2-44. Calculated spin density with an isosurface of ±0.002 a.u., orbital energies (in eV) and isosurfaces (±0.035 a.u.) of frontier molecular orbitals computed for monoradicals 128 (left) and 129 (right). The HOMO-SOMO energy differences are averaged over the highest occupied spin orbital energies. Oxidation potentials and separation of the two first oxidation potentials in V vs. SCE, theoretical (calc.) and experimental (exp.) dihedral angles between the carbazole fragments.

by the easier formation of monoradical 128 +

 128 (EOx = 0.92 V vs. SCE) than 129 + (EOx = 1.14 V vs. SCE, Figure 2-48), and theoretically reproduced by the corresponding calculated vertical ionization potentials, which indicate a higher value for 129 (5.42 eV) than 128 (5.16 eV, Figure 2-47); The difference amounts of 25 kJ/mol. An additional notable difference between 128 + and 129 +

Figure 2 -

 2 45, oxidation of monoradical with SHI may result in a diradical with triplet ground state multiplicity, in accordance the chirality nature of the molecule, this possible diradical formation could be one of the rare examples of chiral organic diradical with a triplet ground state (see chapter 1.5).

Figure 2 - 45 .

 245 Figure 2-45. Schematic illustration of the electronic configurations that can be obtained upon oxidation of a radical exhibiting a SOMO/HOMO inversion.

Figure 2 - 46 .

 246 Figure 2-46. Cyclic voltammograms of 128 (black), 129 (red), 130 (green) and 131 (blue) versus saturated calomel electrode (SCE) as the reference and 0.2 M Bu4NPF6 in dichloromethane with Fc/Fc + as internal standard.

higher for helical radical 131 +Figure 2 - 47 .Scheme 2 - 12 .Figure 2 - 48 .Figure 2 - 52 )

 131247212248252 Figure 2-47. UV-vis-NIR absorption spectra during the electrochemical oxidation of 128 (left), 130 (middle), and 131 (right). The spectra were measured in dichloromethane with 0.2 M n-Bu4NPF6 at 298 K.

Figure 2 -

 2 Figure 2-49. a) EPR spectra of monoradicals (128 with AgBF4 (black), 130 (green), and 131 (blue) with magic blue) in dichloromethane at 298 K. b) Simulated EPR spectra of 130 suggesting the presence of organic radical with ½ spin. g refers to g-value of the free electron, lineshape refers to a value of Lorentzian content of line, and simple LW refers to a value of the constant spectral linewidth in Gauss.

Figure 2 - 50 .

 250 Figure 2-50. UV-vis-NIR absorption spectra of 130 in dichloromethane (5 × 10 -5 M) under argon atmosphere (left) and air atmosphere (right) at 298 K.

Figure 2 - 51 .

 251 Figure 2-51. Left: Zeroth-order fitting plot of absorption of 130 + as a function of time under argon atmosphere. Right: Zero-order fitting plot of absorption of 130 + as a function of time under air atmosphere.

Figure 2 - 52 .

 252 Figure 2-52. LRMS spectrum (dithranol, dichloromethane) of the sample obtained after a reduction of monoradical cation 130 after 96 h. The spectrum suggested that the radical decomposition of 130 was not associated with any oligomerization.

Figure 2 - 53 .

 253 Figure 2-53. Experimental (Expt.) and calculated (Calc.) absorption spectra for 130 (black), 130 + (red), and 130 2 2+

Figure 2 - 54 .

 254 Figure 2-54. Calculated spin density with an isosurface of ±0.002 a.u., orbital energies (in eV), and isosurfaces (±0.035 a.u.) of frontier molecular orbitals computed for monoradicals 130 + (left) and diradical 130 2 2+ (right). The HOMO-SOMO energy differences are averaged over the highest occupied spin orbital energies.

Figure 2 -

 2 Figure 2-55. a) ECD spectra and b) absorption dissymmetry factor (gabs) spectra of compound 130 + SbCl6 -(black) and 130 2 2+ •2SbCl6 -(red) in acetonitrile form NIR-ECD recorded in the range from 400 to 1100 nm (ca. 10 -3 M) at 298 K.

  Figure 2-56, left).[113] Given the high stability of 130 2 2+ •2SbCl6 -(more than 66 hours in solid state, Figure 2-57), superconducting quantum interference device (SQUID) measurements were also performed on the powder of 130 2 2+ •2SbCl6 -at a magnetic field strength of 1 T to investigate the spin interaction. By plotting MT vs. T, a molar susceptibility of C = 0.79 cm 3 K mol -1 was determined at 298 K for 130 2 2+ •2SbCl6 -(Figure 2-56, right). The molar susceptibility started to decrease for temperatures below 170 K, indicating a singlet ground state nature. The energy difference between the two spin states appeared extremely sma

Figure 2 - 56 .Figure 2 - 57 .

 256257 Figure 2-56. Left: Variable temperature EPR spectra of diradical 130 2 2+ ( = 9.4858 GHz). Inset: Half-field region showing no forbidden transition after 100 scans. Right: SQUID magnetometry of solid diradical 130 2 2+ •2SbCl6 - MT vs T at H = 1 T in the MT vs T data, corrected for diamagnetism.

  solvent polarity plays a crucial role in spin distribution and radical stability. Their corresponding diradicals showed near-infrared electronic circular dichroism responses up to 1100 nm and almost degenerate singlet-triplet ground states with weak antiferromagnetic interactions evaluated by VT-EPR. Theoretical calculations highlighted the SHI configuration in both mono-and di-radical states and its role in their mono-and diradicals stability. To the best of our knowledge, they represent the first examples of diradical with SHI and ECD sign inversion as a function of the solvent, which may attract strong interest for their ability to show chirality-induced-spin-selectivity (CISS) effect. 100

bicarbazole radical 128 Scheme 3 - 1 and

 12831 Scheme 3-1 and Figure 3-1b. As a result, the formation of -carbazole dimer in pathway Asuggests the possibility to increase the radical stability of helical bicarbazole, through delocalization of the unpaired electron on an -conjugated system.

Figure 3 - 1 .

 31 Figure 3-1. Possible oligomerization pathway for axial and helical bicarbazoles.

designed and obtained two new tetracarbazoles 132 and 133 ,

 133 presenting an extended conjugation pathway at positions , together with a model bicarbazole 134 for comparative study (Figure 3-2).

Figure 3 - 2 .

 32 Figure 3-2. Tetracarbazoles 132 -133 and model -bicarbazole 134 investigated in this chapter. The blue shade is highlighting the helical bicarbazole part in the system.

Scheme 3 - 2 .

 32 Scheme 3-2. Possible isomers of 132 from the oxidative coupling of rac-129.

Figure 3 - 3 . 1 H

 331 Figure3-3.1 H NMR of the obtained crude mixture of 132 and 132b after a first column chromatography, resulting from the dimerization of racemic starting material in CD2Cl2 at 298 K. The red circles determine the major product and the black squares determine the minor product Discussion regarding the NMR characterizations of the enantiopure compounds of 132 will be detailed later (vide infra).

Figure 3 - 4 .Scheme 3 - 3 .Scheme 3 - 4 .Scheme 3 - 5 .

 34333435 Figure 3-4. a) Chromatogram of analytical HPLC from crude product showing the presence of two enantiopure (+)-132 and (-)-132 and one meso compound 132b. b) ECD signal corresponding to chromatogram a). The chiral stationary phase is (S,S)-Whelk-O1, and the mobile phase is heptane/ethanol/dichloromethane (20/40/40). Note: Discussion regarding the NMR characterization of the enantiopure 132 will be in the dedicated part (vide infra).

Scheme 3 - 6 .

 36 Scheme 3-6. Synthetic route towards 134. Reaction conditions: (i) DDQ, TFA, DCM, a mixture of several products; (ii) K2CO3, Pd(PPh3)4, DMF/H2O, Ar, 110 o C, 50%.

and H 7 in 132 and H 5

 1325 and H in 133 of the inner carbazole units and the aromatic rings of the peripheral carbazole fragments (H-centroid distances between 2.933 and 3.285 Å, Figure 3-5g. These interactions seem to be also present in solution since the 1 H NMR signal of the H 7 proton of the -bicarbazole unit in 132 appears highly shielded with a doublet at 5.54 ppm while for 133, H 7 appears moderately shielded as a doublet at 6.64 ppm compared to the obtained double signals at 7.25 and 7.14 ppm in model bicarbazoles 129 and 132, respectively (Figure 3-6). Deeper analysis of the 1H NMR spectra of these compounds also highlights these structural differences. Most internal bicarbazole proton signals are affected by the ring current of peripheral carbazole and shielded to the high field region, see

Figure 3 - 5 .

 35 Figure 3-5. X-ray structures of (+)-132, 133 -diethyl--bicarbazole. a) Side view and b) top view of 132, c) side view and d) top view of 133, and c) side view and d) top view of -diethyl--bicarbazole with the corresponding dihedral angle of -bicarbazole fragments ( a) an -bicarbazole fragments ( b). Solvent and hydrogen atoms are omitted for clarity. -bicarbazole was taken from ref 4 (CCDC#1865706). Arrows in the top view suggest the orientation of N-CH3 bonds, which are in trans direction for 132 -diethyl--bicarbazole while 133 depicts in a cis direction. g) X-ray structures of 132 and 133 highlighted CH-H 5 and H 7 in 132 and H 5 and H 5 in 133.

Figure 3 - 6 . 1 H

 361 Figure 3-6. 1 H NMR spectra of compounds 129 and 132-134 (in CDCl3) in aromatic region (400 MHz, 298 K).

Figure 3 - 7 .

 37 Figure 3-7. Possible conformer of 132.

10 - 5 - 1

 1051 and rationalized by (TD)-DFT calculations performed by Dr. Laura Abella and Pr. Jochen Autschbach (University at Buffalo, State University of New York, USA). Solvent effects were included by means of the polarizable continuum model (PCM) for dichloromethane to match the experimental conditions. i. UV-visible spectroscopy Tetracarbazoles 132, 133, and bicarbazole 134 display similar UV-vis spectra, which appear more intense and slightly different for the lower energy region than the one recorded for 129. The UV-vis spectra show a broad maximum of absorption between 280 and 330 nm ( = 7.2, 6.5 and 5.1 × 10 4 M -1 cm -1 , for 132, 133 and 134, respectively) and a less intense vibronic pattern between 340 and 415 nm ( 1.5 × 10 4 M -1 cm -1 , Figure 3-8). The red-shift observed for the low energy band for 132 and 133, in comparison to 129, clearly indicate the extension of the -conjugated system for these new derivatives. The expected difference in absorption intensity between 132, 133, and 134 can be readily explained by the number of bicarbazole building blocks in the two formers (two units of 4--and one unit of -for 132 and one unit of 4-and two units of 6-133, respectively).

Figure 3 - 8 .For both tetracarbazole 132 and 133 ,

 38133 Figure 3-8. UV-vis spectra of compound 129 (black), 132 (blue), 133 (green), 134 (red) in dichloromethane (ca. 10 -5 M) at 298 K.

Figure 3 - 9

 39 Figure 3-9 displays the experimental vs. calculated absorption spectra for the most stable conformer of dimers 132 and 133. Besides a small blue shift of 0.1-0.3 eV in the calculations, the experimental and computational spectra are in good agreement. Two dominant spectral bands with distinct intensities can be identified for 132 and 133, which are assigned from low to high energy as follows: 132, HOMO to LUMO and HOMO to LUMO+4; 133, HOMO to LUMO, and a mixture of HOMO-1 to LUMO+4 and HOMO to LUMO+5. The corresponding molecular orbitals of 132 and 133 associated with the most intense excitations are provided in Tables 3-4 and 3-5.

Figure 3 - 9 .

 39 Figure 3-9. Calculated (Calc.) absorption spectra for (+)-132 (blue) and (+)-133 (green). Selected transitions and oscillator strengths are Tables 3-4 and 3-5.

Figure 3 - 10 .

 310 Figure 3-10. ECD spectra of compound (+)-129 (black), (+)-132 (blue) and, (+)-133 (green) in dichloromethane (ca. 10 - 5 M) at 298 K. Corresponding ( )-enantiomers are represented in grey lines.

Figure 3 - 11 .

 311 Figure 3-11. Calculated electronic circular dichroism (ECD) spectra for (+)-132 (blue) and (+)-133 (green).

Figure 3 - 12 .Figure 3 - 12 .

 312312 Figure 3-12. Normalized luminescence spectra of compound 129 (black), 132 (blue), 133 (green), 134 (red) in dichloromethane (ca. 10 -6 M) at 298 K.

Figure 3 -

 3 Figure 3-13. a) CPL spectra of compounds (+)-129 (black), (+)-132 (blue), and (+)-133 (green) in dichloromethane (ca. 10 -5 M) at 298 K. b) gabs spectra of compounds (+)-132 (blue) and (+)-133 (green) in dichloromethane (ca. 10 -5 M) at 298 K. Corresponding (-)-enantiomers are represented in dashed lines.

  -14a), with the latter corresponding to a two-oxidation process, as evidenced by differential pulse voltammetry (DPV, Figure3-14b).Compound 133 exhibits two consecutive sets of two one-oxidation processes at 0.84 and 0.93 V, and at 1.23 and 1.27 V. The presence of oxidation events at lower potentials for 132 and 133 than for 129-bicarbazole fragment, as confirmed by the CV of model 134, which shows one reversible oxidation at 0.76 V, followed by an irreversible event at ca. 1.11 V vs.SCE.In line with the previous characterizations, 133 thus appears bicarbazole fragments while 132 is an intermediate case between compounds 129 and 134. It is noteworthy to mention that the reversibility difference observed for the oxidation events when comparing 132 and 133 to model bicarbazoles 129 and 134 highlights an important role of the peripheral carbazole substituents.

  to a solution of 132, 133, and 134 in dichloromethane quantitatively afforded persistent monoradicals 132 + SbCl6 -, 133 + SbCl6 -, and 134 + SbCl6 -, respectively -bicarbazole 129 (see chapter 2). The obtained three persistent radicals display similar UV-vis-NIR absorption spectra with notably a 13-18 × 10 3 M -1 cm -1 , Figure 3-15a), weak signals between 500 and 800 nm, followed by a broad NIR signature from 800 nm to 2000 nm ( 5-13 × 10 3 M -1 cm -1 , Figure 3-15a) with three main peaks around 900, 1320, and 1700-2000 nm. These obtained spectra are strongly different than the characteristic one obtained for the stable oxidized monocarbazole (see chapter 2), indicating a much stronger electron delocalization of the unpaired electron in the monoradical tetracarbazole derivatives. Since a similarity was observed between the absorption spectra of 132 + , 133 + , and 134 + , this suggests that the electron delocalization occurs on the -bicarbazole fragment of each derivative. Theoretical calculations further confirm this aspect, and notably reveal a spin density for 132 + , 133 + , and 134 + mainly delocalized on the two phenyl rings and the linked nitrogen atoms of the -bicarbazole fragments (Figure 3-15c).

Figure 3 -

 3 Figure 3-15. a) UV-vis-NIR absorption spectra of 132 + SbCl6 -(blue), 133 + SbCl6 -(green), and 134 + SbCl6 -(red). measured in dichloromethane (c = 10 -5 M) at 298 K. b) Calculated UV-Vis-NIR spectra for 132 + (blue), 133 + (green), and 134 + (red). c) Calculated spin density with an isosurface of ±0.002 au for monoradicals 129 , 132 , 133 , and 134 .

Figure 3 - 16 .

 316 Figure 3-16. Time-dependent UV-vis-NIR absorption spectra of (a) 132 + SbCl6 -, (b) 133 + SbCl6 -, and (c) 134 + SbCl6 - in dichloromethane under air-saturated atmosphere at 298 K. d) Second-order fitting plot of of 132 + SbCl6 -as a function of time at 1750 nm (blue), 133 + SbCl6 -as a function of time at 1550 nm (green), and 134 + SbCl6 -as a function of time at 950 nm (red). The EPR responses of these three persistent monoradical cations were recorded and displayed a similar broad intense doublet signal centered at 338.2, 338.4 and 339.2 mT for 132 + SbCl6 -, 133 + SbCl6 -, and 134 + SbCl6 -, respectively, characteristic of organic nitrogenbased radicals (g = 2.00, Figure 3-17). All the EPR spectra were reproducible by EPR simulation and thus confirmed the presence of a spin (ms = ½) in the system (Figure 3-18).

Figure 3 - 17 .

 317 Figure 3-17. EPR spectra of monoradical (132 + SbCl6 -(blue), 133 + SbCl6 -(green), and 134 + SbCl6 -(red)) in dichloromethane at 298 K.

Figure 3 - 18 .Scheme 3 - 8 .

 31838 Figure 3-18. Simulated EPR spectra of monoradicals a) 132 + SbCl6 -, b) 133 + SbCl6 -, and c) 134 + SbCl6 -.

Figure 3 - 19 .

 319 Figure 3-19. UV-vis-NIR absorption spectra of a) 132 + SbCl6 -, b) 133 + SbCl6 -, and c) 134 + SbCl6 -in dichloromethane (DCM, black) and acetonitrile (MeCN, blue), (c = 5 × 10 -5 M) at 298 K.

Figure 3 - 20 .

 320 Figure 3-20. Time-dependent UV-vis-NIR absorption spectra of (a) 132 + SbCl6 -, (b) 133 + SbCl6 -, and (c) 134 + SbCl6 - in acetonitrile under air atmosphere at 298 K.

Figure 3 -Figure 3 - 22 .

 3322 Figure 3-21. a) First-order fitting plot of of 132 + SbCl6 -as a function of time at 915 nm (blue), 133 + SbCl6 - as a function of time at 1550 nm (green), and 134 + SbCl6 -as a function of time at 950 nm (red). b) Half-life time values (t1/2) of monoradicals 132 + 2SbCl6 -, 133 + SbCl6 -, and 134 + SbCl6 -in dichloromethane (DCM) and acetonitrile (MeCN)under air atmosphere at 298 K.

Figure 3 - 22 .

 322 Figure 3-22. NIR-ECD of in situ generated monoradicals a) (+)-132 + SbCl6 -and b) (+)-133 + SbCl6 -in dichloro-methane (black) and acetonitrile (blue) at 298 K with their corresponding (-) enantiomers marked as grey lines.

Figure 3 - 23 .

 323 Figure 3-23. Calculated ECD spectra of (+)-132 + (left) and (+)-133 + SbCl6 -(right).

Figure 3 - 24 .

 324 Figure 3-24. Calculated spin density with an isosurface of ±0.002 au, orbital energies (in eV) and isosurfaces (±0.035) of frontier molecular orbitals computed for monoradicals a) 129 , b) 134 , c) 132 , and d) 133 . The HOMO-SOMO energy differences are averaged over the highest occupied spin-orbital energies.

  chapter. Mixing AgBF4 in a dry dichloromethane solution of 134 resulted in an instantaneous oligomerization reaction as observed from the loss in overall absorption (Figure 3-25b), in line with the obtained irreversible nature of the second oxidation process in cyclic voltammogram (Figure 3-14, vide supra). Although the diradical 134 was not stable enough to be obtained, the DFT calculations of this diradical suggest the diradical 134 possesses a triplet ground state

Figure 3 - 123 ii. Generation of diradical 134 , 132 and 133 Scheme 3 - 9 .

 312313413213339 Figure 3-25. a) Attempts to generate diradical 134 2 2+ using different chemical oxidation conditions. b) UV vis NIR absorption spectra of 134 (black), 134 + SbCl6 -(red), and 134 n n+ BF4 -(blue) in dichloromethane at 298 K. c) Calculated orbital energies (in eV) and isosurfaces (±0.035 au) of frontier molecular orbitals computed for diradicals 134 2 2+ .

Figure 3 - 26 .

 326 Figure 3-26. Top: UV vis NIR absorption spectra of a) 132 (black), 132 + SbCl6 -(red), and 132 2 2+ •2SbCl6 -(blue), b) 133 (black), 133 + SbCl6 -(red), and 133 2 2+ •2SbCl6 -(blue) in dichloromethane at 298 K. Bottom: c) 132 (black), 132 + SbCl6 -(red), and 132 2 2+ •2SbCl6 -(blue), d) 133 (black), 133 + SbCl6 -(red), and 133 2 2+ •2SbCl6 -(blue) in acetonitrile at 298 K.

  -26c), suggesting the presence of a more localized carbazole radical together with conjugated bicarbazole radical as suggested by calculated spin density of 132 2 2+ (Figure 3-34, vide infra). The calculated spectra in dichloromethane for both diradicals reproduced well the experimental one and notably allowed us to assign the low-energy bands between 700 and 1600 nm to excitations to the LUMO and LUMO+1 (Figure 3-27).

Figure 3 - 27 .

 327 Figure 3-27. Calculated absorption spectra for the most stable conformer of neutral, monoradical, and diradical 132 (left) and 133 (right) vs. the corresponding experimental (Expt.) spectra of the diradical in dichloromethane. Selected transitions and oscillator strengths are

- 28 ) 2 =Figure 3 - 28 .

 282328 Figure 3-28. Half-life time values (t1/2) of diradicals 132 2 2+ •2SbCl6 -and 133 2 2+ •2SbCl6 -in dichloromethane (DCM) and acetonitrile (MeCN) under inert atmosphere at 298 K.

Figure 3 -Figure 3 -Figure 3 -Figure 3 -

 3333 Figure 3-29. a) Kinetic UV-vis-NIR absorption of 132 with time in dichloromethane (5 × 10 -5 M) under inert atmosphere at 298 K. b) a plot of the absorbance ratio of 132 between 550 and 1475 nm. Corresponding half-life time (t1/2) is defined as the intersection between the two linear plots namely fast and slow decay respectively.

Figure 3 - 33 .

 333 Figure 3-33. Left: Molecular structures of 132 (top) and 133 (bottom), where the red shade highlights the spin density of the SOMOs and the blue shade highlights the spin density of the HOMOs. Right: Calculated spin density with an isosurface of ±0.002 au for the most stable conformer of diradicals 132 and 133 .

Figure 3 - 34 .

 334 Figure 3-34. Orbital energies (in eV) and isosurfaces (±0.035) of frontier molecular orbitals computed for diradicals 132 2 2+(left) and diradical 133 2 2+ (right). The SOMO-SOMO energy differences are .

Figure 3 - 35 .

 335 Figure 3-35. ECD spectra of neutral (black), monoradical (red), and diradical (blue) of a) (+)-132 and b) (+)-133 in dichloromethane, c) 132 and d) 133 in acetonitrile form NIR-ECD recorded in the range from 400 to 1100 nm (ca. 10 -3 M) at 298 K. Corresponding (-)-enantiomers are represented in grey lines.

Figure 3 - 37 .

 337 Figure 3-37. EPR spectra of diradicals 132 2 2+ •2SbCl6 -(blue) and 133 2 2+ •2SbCl6 - = 9.4858 GHz).

Figure 3 - 37 .

 337 Figure 3-37. Variable temperature EPR spectra of diradicals a) 132 2 2+ •2SbCl6 -and b) 133 2 2+ •2SbCl6 -( = 9.4858 GHz). c) IT vs. T plot of frozen solution of diradicals 132 2 2+ •2SbCl6 -(blue) and 133 2 2+ •2SbCl6 -(green) in dichloromethane.

Figure 4 - 0 .

 40 Figure 4-0. Indenocarbazole and diindenocarbazole-based radicals described in this chapter

Figure 4 - 1 .

 41 Figure 4-1. Structural comparison of 9H-carbazole, 9H-fluorene, and phenalene together with their corresponding radical species.

Figure 4 - 2 .

 42 Figure 4-2. Fluorenyl-based radical 138 and 139.

Figure 4 - 3 .

 43 Figure 4-3. Dibenzofluorenyl-based radicals 140a-c with anthryl-protecting group.

Figure 4 - 4 .

 44 Figure 4-4. Fluorenyl-based radicals with alkynyl protecting group 141a-c and their corresponding intermolecular coupling products 142 and 143b-c.

Figure 4 - 5 .

 45 Figure 4-5. Fluorenyl-based radicals with oxasmaragdyrin protecting group 144.

Figure 4 - 6 .

 46 Figure 4-6. Fluorenyl-based diradicals and diradicaloids with anthryl protecting groups 145 and 146a-c.

Figure 4 - 7 .

 47 Figure 4-7. a) Examples of fluorenyl-based singlet ground state diradical 147 and its oxidized product 148. b) VT-EPR of diradical 147 showing the antiferromagnetic singlet ground state with its corresponding forbidden transition at 163 K. Figure was reproduced from ref 12.

Figure 4 - 8 .

 48 Figure 4-8. Examples of fluorenyl-based diradicaloid 32, 89, 149-151.

Figure 4 - 9 .

 49 Figure 4-9. Examples of indenocarbazole-based polyradicaloids 152a-c.

Scheme 4 - 1 .

 41 Scheme 4-1. Generation of fluorenyl-based radicals.

Figure 4 - 10 .

 410 Figure 4-10. Target diindenocarbazole 173.

Scheme 4 - 2 .

 42 Scheme 4-2. Schematic synthetic route towards indenocarbazole 155a-b. Reaction conditions: (i) 2-formylboronic acid (for 153a) or 2-formyl-5-methylphenylboronic acid pinacol ester 160 (for 153b), K2CO3, Pd(PPh3)4, DMF/H2O, ; (ii) 2-MesMgBr, THF, Ar, -78 rt. (iii) BF3OEt2 iv. B2Pin2, KOAc, Pd(dppf)Cl2, 1,4-

Figure 4 -

 4 Figure 4-11. X-ray structure of compound 155a. Hydrogen atoms (except at the fluorenyl position) have been omitted for clarity reasons.

Figure 4 -

 4 Figure 4-12. 1 H-NMR spectrum of compound 155a and 155b in CD2Cl2 at 298 K.

- 5 - 1 .Figure 4 - 13 ).Figure 4 - 13 .

 51413413 photophysical properties of 155a by around 5 nm (Figure4-13).

Figure 4 - 14 .

 414 Figure 4-14. ECD spectra of compound (+)-155a (black) and (+)-155b (red) in dichloromethane at 298 K. Corresponding (-) enantiomers were shown in grey.

Figure 4 - 15 .

 415 Figure 4-15. Cyclic voltammograms of 155a (black) and 155b (red) versus saturated calomel electrode (SCE) as the reference and 0.2 M Bu4NPF6 in dichloromethane with ferrocene as internal standard.

Scheme 4 - 3 .

 43 Scheme 4-3. Synthesis of fluorenyl-based radical 157 and subsequent oxygenated species 158. i) 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), dichloromethane, Ar, rt.

Figure 4 -

 4 Figure 4-16. 1 H NMR spectra in the aliphatic region of hydroindenocarbazole 155a and p-quinonemethidocarbazole 158 in CD2Cl2 at 298 K.

Figure 4 -

 4 Figure 4-17. 1 H NMR spectra in the aromatic region of hydroindenocarbazole 155a and p-quinonemethidocarbazole 158 in CD2Cl2 at 298 K.

Figure 4 -

 4 Figure 4-18. 13 C NMR spectrum of p-quinonemethidocarbazole 158 in CD2Cl2 at 298 K indicating the presence of C=O bond.

Figure 4 - 19 . 146 Scheme 4 - 4 .Figure 4 - 20 .Figure 4 - 21 ).Scheme 4 - 5 .Figure 4 - 21 .Scheme 4 - 6 .Scheme 4 - 7 .

 41914644420421454214647 Figure 4-19. LRMS spectrum (dithranol, dichloromethane) of the p-quinonemethidocarbazole 158.

Figure 4 -- 8 .Scheme 4 - 8 .

 4848 Figure 4-24. a) 1 H NMR spectrum of a mixture of diastereomer 172 and 173 in CD2Cl2 at 298 K. b) Chromatogram of analytical HPLC from crude product showing the presence of two diastereomers 172 and 173. The chiral stationary phase is (S,S)-Whelk-O1, and the mobile phase is heptane/dichloromethane (80/20).

Figure 4 -

 4 Figure 4-25. 1 H NMR spectrum in the aliphatic region of diastereomers 172 and 173 compared to model indenocarbazole 155b in CD2Cl2 at 298 K.

Figure 4 -

 4 Figure 4-26. 1 H-1 H COSY between the aliphatic and aromatic region of 172 in CD2Cl2 at 298 K.

Figure 4 -

 4 Figure 4-27. 1 H-1 H COSY between the aliphatic and aromatic region of 173 in CD2Cl2 at 298 K.

Figure 4 - 28 .

 428 Figure 4-28. Top: 1 H-1 H COSY correlation between fluorenyl protons H 7 and H 7 for 172 and 173 in CD2Cl2 at 298 K. Bottom: 1 H-1 H NOESY correlation between fluorenyl protons H 7 and H for 173 in CD2Cl2 at 298 K. (NOESY correlation for 172 is currently investigating).

Figure 4 - 29 .

 429 Figure 4-29. UV-vis absorption (thick line) and fluorescence (dash line) spectra of compounds 155b (black), 172 (red) and 173 (blue) in dichloromethane (ca. 10 -5 M) at 298 K.

173 Figure 4 - 172 Figure 4 - 29 .

 1734172429 Figure 4-30. a) ECD spectra of (+)-155b (black), (+)-172 (red), and (+)-173 (blue) in dichloromethane at 298 K. b) gabs spectra (solid line) of (+)-172 (red) and (+)-173 (blue) and glum spectra (dash line) of (+)-172 in dichloromethane at 298 K. The corresponding (-) enantiomers are shown in grey line.

Figure 4 -

 4 Figure 4-30. 1 H-NMR spectra of diastereomer mixture 172 and 173 (top) and a mixture after purification from dehydrogenation-oxidation reaction (bottom) in CD2Cl2 at 298 K.

Figure 4 -

 4 Figure 4-31. a) Kinetic UV-vis-NIR absorption of 173 in dichloromethane (6 × 10 -4 M) filled with argon at 298 K.

Figure 4 - 32 .

 432 Figure 4-32. LRMS spectrum (dithranol, dichloromethane) of the radical species after the UV-vis-NIR kinetic measurement for 7 days indicating the presence of oxygenated species.

1 Figure 4 -

 14 Figure 4-33. a) Variable temperature EPR spectra of 173 2 . b) IT vs. T plot of frozen solution of diradicals of 173 2 in dichloromethane.

Figure 4 - 34 .

 434 Figure 4-34. Left) Proposed oxidation of 173 . Right) A preliminary experiment of oxidation of 173 with portions of magic blue oxidant.

Figure 4 -

 4 Figure 4-35. a) Example of organic radicals on surfaces. [25] b) Proposed example of chiral organic radicals on surfaces.

Figure B- 2 .

 2 Figure B-2. Carbazole-based persistent radicals in this thesis.

Figure B- 3 .

 3 Figure B-3. Diindenocarbazole diastereomers 172 and 173.

Figure B- 3 .

 3 Figure B-3. Proposed design of redox-active chiral organic molecule on the surface.

Figure B- 4 .

 4 Figure B-4. Recent reported BICOL-based donor-acceptor systems.

1 H

 1 NMR (400 MHz, CD2Cl2 3 J = 8.8 Hz, 2H 2 ), 7.44 (d, 3 J = 8.8 Hz, 2H 1 ), 7.34 (d, 3 J = 8.2 Hz, 2H 8 ), 7.28 (ddd, 3 J = 8.2, 6.9, 5 J = 1.3 Hz, 2H 7 ), 6.66 (ddd, 3 J = 8.0, 7.0, 5 J = 1.1 Hz, 2H6 ), 6.53 (dt, 3 J = 7.9, 5 J = 0.9 Hz, 2H 5 ), 3.93 (s, 6H 3 ), 3.75 (d,5 J = 4.2 Hz, 6H 9 ) 13 C NMR (101 MHz, CD2Cl2 C 7 -H), 122.5, 122.0, 121.4 (C 5 -H), 120.0, 118.0 (C 6 -H), 112.1 (C 1 -H), 108.1 (C 8 -H), 108.0 (C 2 -H), 57.6 (OC 3 H3), 29.1 (N-C 9 H3).

  3 (C 1 -H), 109.0 (C -H), 108.1 (C 1 -H, C 8 -H), 104.3 (C 5 -H), 104.0 (O-C 3 -H-O), 56.3 (O-C -H), 29.7 (C -H ), 29.1 (C 9 -H). HR-MS Thermo-Fisher Q-Exactive, ESI (+), CH3OH/CH2Cl2 (90/10); ion [M+Na] + , C55H42N4O4Na, m/z calculated 822.32006, m/z 6,6'-Dimethoxy-9,9'-dimethyl-9H,9'H-3,3'-bicarbazole -134

R1

R1

  second fraction by preparative separation 128 are dissolved in 4.2 mL of dichloromethane. S,S)-Whelk-O1 (250 x 4.6 mm), hexane / dichloromethane (75/25) as mobile phase, flow-rate = 5 mL/min, UV detection at 254 nm.

k enantiomerisation = 9 .

 9 40.10 -8 s -1 (180°C, 1,2-dichlorobenzene) G = 173.5 kJ.mol -1 (180°C, 1,2-dichlorobenzene) t1/2 = 43 days (180°C, 1,2-dichlorobenzene) chiral HPLC separation for compound 155b column, and detected with an UV detector at 254 nm and a circular dichroism detector at 254 nm. The flow-rate is 1 mL/min.

Figure F- 1 .

 1 Figure F-1. Configuration électronique à couche fermée et ouverte et les propriétés spécifiques.

Figure F- 2 .Figure F- 3 .

 23 Figure F-2. Exemples de composés radicalaires chiraux décrits dans la littérature.

[17- 19 ]

 19 revisité la synthèse de BICOL et de ses dérivés pour caractériser leurs propriétés photophysiques et chiroptiques, à la fois expérimentalement dièdre entre les deux unités bicarbazole 128 et 129 avec deux chiralités différentes, nommées axiale vs. hélicoïdale (Figure F-4b).

Figure F- 5 .

 5 Figure F-5. a) BINOL et BICOL analogues. b) monocarbazole 128b, bicarbazole axial 128, and bicarbazole hélicoïdal 129 sans fonctionnalisation en position 6.

3 IFigure F- 5 .

 35 Figure F-5. Spectres ECD (ligne épaisse) et spectres CPL (tirets) des composés (+)-128 (noir) et (+)-129 (rouge) dans le dichlorométhane (environ 10 -5 M) à 298 K. Les énantiomères (-) sont représentés par des lignes grises.

Figure F- 6 .

 6 Figure F-6. Densité de spin calculée avec une isosurface de ±0,002 au, énergies orbitales (en eV) et isosurfaces (±0,035) des orbitales moléculaires frontières calculées pour les monoradicalaires 128 (à gauche) et 129 (à droite). Les différences d'énergie HOMO-SOMO sont moyennées sur les énergies orbitales de spin les plus occupées. Potentiels d'oxydation et séparation des deux premiers potentiels d'oxydation dans V vs. SCE, angles dièdres théoriques (calc.) et expérimentaux (exp.) entre les fragments de carbazole.

Figure F- 7 .

 7 Figure F-7. Illustration schématique de la formation de configurations électroniques diradicalaires triplet lors de l'oxydation d'un radical présentant une inversion SOMO/HOMO et les structures moléculaires des composés 130 et 131.

Figure F- 8 .

 8 Figure F-8. À gauche : spectres de facteur de dissymétrie d'absorption (gabs) du diradical (+)-130 2 2+ •2SbCl6 -(rouge) acétonitrile pour des ECD enregistrés dans une plage de 400 à 1100 nm (environ 10 -3 M) à 298 K. Énantiomères correspondants (-) marqués d'une ligne grise. À droite : magnétométrie SQUID du diradical solide 130 2 2+ •2SbCl6 -: tracés de MT vs T à H = 1 T en montée en température. Données MT vs. T, corrigées du diamagnétisme.

Figure F- 9 .Figure F- 10 .

 910 Figure F-9. Les tétracarbazoles 132 -133 et le modèle 6,6'-bicarbazole 134 étudiés dans le chapitre 3. La teinte bleue met en évidence la partie hélicoïdale du bicarbazole dans le système.

Figure F- 11 .Figure F- 12 .

 1112 Figure F-11. Spectres d'absorption UV-vis-NIR de 132 + SbCl6 -(a) et 133 + SbCl6 -dans le dichlorométhane (DCM, noir) et l'acétonitrile (MeCN, bleu), (c = 5 × 10 -5 M) à 298 K.

  132 a une stabilité 6 fois plus élevée que 133 dans une solution de dichlorométhane sous argon (Figure F-13).

Figure F- 13 .

 13 Figure F-13. Densité de spin calculée avec une isosurface de ±0,002 au, énergies des orbitales (en eV) et isosurfaces (±0,035) des orbitales moléculaires frontières calculées pour les diradicaux 132 2 2+ (à gauche) et 133 2 2+ (à droite). Les différences d'énergie SOMO-SOMO sont notés comme E. Le tableau montre les valeurs de demi-vie des diradicaux 132 2 2+ et 133 2 2+ dans différents solvants (dichlorométhane vs. acétonitrile).

Figure F- 14 .

 14 Figure F-14. Carbazole, fluorène et leurs radicaux correspondants.

Figure F- 15 . 1 )

 151 Figure F-15. Modèles d'indénocarbazole radicalaires et diindenocarbazole diradicalaire étudiés dans le chapitre 4.

1 Figure F- 16 .

 116 Figure F-16. a) Absorption cinétique UV-vis-NIR de 173 dans du dichlorométhane (6 × 10 -4 M) sous argon à 298 K. b) Graphique IT vs. T d'une solution congelée de diradicaux de 173 dans du dichlorométhane.

Table 2 - 1 :

 21 Optimization of the synthesis of (±)-BICOL via oxidative coupling reaction.

	Entry	Reaction time	O2 source	Solvent	VO(acac)2 loading	Reaction Scale	Yield
	1	6+7+7 h	Ambient airflow		5-10 mol%	50 mg	65 %
	2	24 h	O2 Bubbling		10 mol%	100 mg	45 %
	3 4	24 h 24 h	Ambient airflow Ambient airflow	MeCN	10 mol% 10 mol%	200 mg 1 g	66 % 63 %
	5	24 h	Ambient airflow		10 mol%	2.4 g	60 %
	6	24 h	Ambient airflow		10 mol%	3 g	45 %

Table 2 - 2

 22 Different chemical shifts (ppm) in 1 H-NMR between compounds 128 and 129.

	Proton position	Chemical shift for 128 (ppm)	Chemical shift for 129 (ppm)	Chemical shift difference (ppm)
	1	7.44	7.49	0.05
	2	7.58	7.56	0.02
	5	6.95	6.53	0.42
	6	6.53	6.66	0.13
	7	7.28	7.25	0.03
	8	7.34	7.35	0.01

rac-130 and rac-131 crystallized in the P21/n space groups and displayed dihedral angles between 98 and 102 for rac-130 rac-131 (Figure 2-26). However, there were two conformers observed for 130 in the calculations with dihedral angles of 65 and 106.6 (Boltzmann population of 4% at 298 K). Therefore, 130 did not crystallize in its lowest energy conformer. The calculated properties of 130 further support the higher abundance of the conformer with a dihedral angle of 65 in solution by comparison with the experimental chiroptical properties (vide infra).

Table 2 - 3

 23

(vide infra).

Table 2 -

 2

3 Specific and molar rotations measured for the enantiopure compounds together with the values of BICOL for

  2

Table 2 - 4 .

 24 Selected excitations and occupied (occ)-unoccupied (unocc) MO pair contributions (greater than 10%) for (+)-

	128.
	Excitation	E [eV]	[nm]	f	R [10 -40 cgs]	occ. no.	unocc no.	%
	#1	3.788	327	0.144	-23.02	HOMO	LUMO	93
	#5	4.355	285	0.117	271.87	HOMO-2	LUMO	91
	#6	4.426	280	0.110	-142.64	HOMO-3	LUMO	88
	#9	5.024	247	0.410	694.34	HOMO	LUMO+2	78
	#12	5.148	241	0.498	-538.15	HOMO	LUMO+3	63

Table 2 - 5 .

 25 Selected excitations and occupied (occ)-unoccupied (unocc) MO pair contributions (greater than 10%) for (+)-

	129.
	Excitation	E [eV]	[nm]	f	R [10 -40 cgs]	occ. no.	unocc no.	%
	#1	3.492	355	0.199	-49.15	HOMO	LUMO
	#2	3.645	340	0.020	-54.73	HOMO-1	LUMO
	#3	4.058	306	0.096	372.62	HOMO -1	LUMO
	#5	4.281	290	0.141	-66.46	HOMO	LUMO +1
	#14	5.202	238	0.742	-805.41	HOMO	LUMO +3
						HOMO -2	LUMO +1

Table 2 -6. Photoluminescence 128-131 in dichloromethane.

 2

	Compound
	128	22
	129	15
	130	24
	131	17
		excitation = 370
	nm. The CPL spectra are depicted in

Table 2 -

 2

	Compound
	128	+0.92	+1.11	+1.63
	129	+1.14	+1.40	-
	128b	+0.95	+1.60	-
	130b	+0.87	+1.63	-

7. Oxidation potential (EOx in V) of 128, 129, 128b, and 130b versus saturated calomel electrode (SCE).

Table 2 -

 2

	Compound	Environment	A	B	r 2	half-life
	128	Air Ar	-0.00306 0.00795	-0.00439 -8.34031×10 -4	0.9944 0.9927	158 ± 29 min 831 ± 48 min
	130b	Air	0.133	-0.000798	0.9438	84 ± 0.2 hours

8. Linear fitting from the first-order fitting equation with half-life calculation of compound 128 +

Table 2 - 9 .

 29 Oxidation potential (EOx in V) of 128-131 versus saturated calomel electrode (SCE) and difference between the

	Compound
	128	+0.92	+1.11	190 mV
	129	+1.14	+1.40	260 mV
	130 (DCM)	+0.87	+1.10	230 mV
	130 (MeCN)	+0.79	+0.98	190 mV
	131	+1.06	+1.37	310 mV

Table 2 -

 2

	Compound	Environment	A	B	r 2	half-life (hours)
	130	Air Ar	0.243 0.634	-0.00125 -0.00342	0.9565 0.9932	97 ± 0.2 93 ± 0.2

10. Linear fitting from kinetic optical density of 130 as a function of time with half-life calculation

Table 3 -

 3

	Meanwhile, the two peripheral carbazoles also experience the ring current from the inner
	bicarbazole. The proton H 4 of 133 is strongly shielded due to the presence of the bicarbazole core
	and appeared at 7.43 ppm (vs. 8.40 ppm in bicarbazole model 134). Additionally, protons in the
	dioxepine group (H

1 for NMR signals summary. Beside proton H

7

, proton H 5 is noteworthy to mention with a different deviation by shielded in 132 and deshielded in 133 comparing to 129 (6.80 and 7.43 vs. 6.95 ppm, respectively). This remarkable difference is presumably caused by the effects of peripheral carbazoles.

3

) of both 132 and 133 have small ring current interaction as observed in a similar chemical shift compared to compound 129. Interestingly, the dioxepine group of 132 showed diastereotopic hydrogens with J coupling equal to 3.3 Hz instead of a sharp singlet signal, system.

Table 3 -

 3

	Proton position	Chemical shift for 129 (ppm)	Chemical shift for 132 (ppm)	Chemical shift for 133 (ppm)	Chemical shift for 134 (ppm)
	1	7.49	7.48	7.64	7.50
	2	7.56	7.48	7.52	7.86
	5	6.95	6.80	7.43	7.69
	7	7.25	5.54	6.64	7.14
	8	7.35	6.95	7.17	7.37
			7.43	7.78
			7.36	7.74
				7.43	8.40 (marked as 4)
			7.05	7.62
		6.52 (marked as 6)	6.57
			7.32	7.14
			7.50	7.32
	3	5.65 (s)	5.64 (d, A )	5.68 (s)

1. The difference in chemical shift (ppm) in 1 H-NMR for compounds 132 and 133 compared to model bicarbazole 129 and 134.

Table 3 -

 3

2 (vide infra).

Table 3 - 2

 32 Specific and molar rotations measured for the enantiopure compounds together with the values of 129 for

	comparison
	Compound	Concentration (g L -1 )	(10 -1 deg•cm 2 •g -1 )	(10 -3 deg•cm 2 •g -1 )
	(+)-129	1.3 × 10 -3	+640	+2,570
	(-)-129	1.1 × 10 -3	-650	-2,640
	(+,+)-132	1.0 × 10 -3	+659	+5,315
	(-,-)-132	1.1 × 10 -3	-659	-5,320
	(+)-133	5.0 × 10 -3	+1,055	+8,680
	(-)-133	5.0 × 10 -3	-1,190	-9,790

Table 3 - 3 .

 33 Isosurfaces (±0.030 au) of HOMO-1, HOMO and LUMO for 132 and 133.

	Compound	HOMO-1	HOMO	LUMO
	132
	133

Table 3 -

 3

	Excitation	E [eV]	[nm]	f	R [10 -40 cgs]	occ. no.	unocc no.	%
	#1	3.191	388	0.076	190.08	HOMO	LUMO	46
	#2	3.302	376	0.050	-141.8	HOMO	LUMO +1	45
	#7	3.829	324	0.077	-136.1	HOMO -2	LUMO +1	27
	#10	4.005	310	0.066	132.2	HOMO	LUMO +2	12
	#11	4.021	308	0.134	237.3	HOMO	LUMO +2	23
	#15	4.174	297	0.358	60.4	HOMO	LUMO +4	33

4. Selected excitations and occupied (occ)-unoccupied (unocc) MO pair contributions for (+)-132.

Table 3 -

 3

	Excitation	E [eV]	[nm]	f	R [10 -40 cgs]	occ. no.	unocc no.	%
	#1	3.281	378	0.066	26.97	HOMO	LUMO	45
	#7	3.944	314	0.057	100.90	HOMO	LUMO +3	40
	#11	4.073	304	0.170	244.40	HOMO -4	LUMO	38
	#12	4.085	303	0.128	-672.48	HOMO -5 HOMO -6	LUMO LUMO	24 16
	#16	4.286	289	0.250	1042.00	HOMO	LUMO +4	32
	#17	4.321	287	0.498	-1043.27	HOMO -1 HOMO	LUMO +4 LUMO +5	19 15

5.

Selected excitations and occupied (occ)-unoccupied (unocc) MO pair contributions for (+)-133.

Table 3 -

 3

	Compound
	129	+1.14	+1.40	-	-
	132	+0.85	+1.15	+1.30	-
	133	+0.83	+0.93	+1.23	+1.27
	134	+0.71	+1.11	-	-

6. Oxidation potential (EOx in V) of 129, 132, 133, and 134 versus saturated calomel electrode (SCE) identified by differential pulse voltammetry (DPV) with ferrocene as internal standard.

Figure 3-14. a) Cyclic voltammograms (CVs) and b) differential pulse voltammograms (DPVs) of 129 (black), 132 (blue), 133 (green), and 134 (red) versus saturated calomel electrode (SCE) as the reference and 0.2 M Bu4NPF6 in dichloromethane with ferrocene as internal standard.

3.

8 Monoradical 132 + , 133 + and 134 + i. Experimental and theoretical investigations Scheme

3-7. Synthetic route to radical 132 + SbCl6 -, 133 + SbCl6 -, and 134 + SbCl6 -.

Table 3 - 7 .

 37 Linear fitting from second-order fitting equation with half-life calculation

	Species	A0	B	r 2	half-life (h)
	132 + SbCl6 -	0.6906	1.58498×10 -4	0.9592	134 ± 8.0
	133 + SbCl6 -	0.4069	0.00277	0.9867	15 ± 0.4
	134 + SbCl6 -	0.6483	0.00394	0.9954	6.5 ± 0.1

Table 3 - 8 .

 38 Linear fitting from second-order fitting equation with half-life calculation

	Species	A0	B	r 2	half-life (min)
	132 + SbCl6 -	0.1888	-0.03046	0.9888	22 ± 8.0
	133 + SbCl6 -	0.1144	-0.01696	0.9968	40 ± 0.4
	134 + SbCl6 -	0.1685	-0.02214	0.9969	31 ± 0.1

  C-NMR, and LRMS. The formation of 158 allowed us to observe a signal in the NMR due to a closed-shell electronic structure instead of the open-shell one. Moreover, this molecular system loses its chirality from the dehydrogenation-oxidation as observed by the combined proton signals in omethyl group (H 15 and H19 ) of the mesithyl group (from 2.97 and 2.30 to 2.23 ppm, Figure4-16)as well as the m-protons (H 16 and H 18 from 7.18 and 6.62 to 7.15 ppm). Furthermore, the disappearance of H11 and the highly shielded signal for H4 in compound 158 suggested the formation of oxidized species (Figure 4-17).

-34).

	1				173 2
					173 3 +
	Absorbance	Fluorenyl radical	Carbazole radical	173 2 2+ 173 3+
	0
		400	800	1200	1600	2000
			wavelength / nm

  H NMR (300 MHz, Acetone-d6 2H 9 ), 7.55 (d, 3 J = 8.6 Hz, 2H 2 ), 7.37 (d, 3 J = 8.1 Hz, 2H 8 ), 7.25 (d, 3 J = 8.6 Hz, 2H 1 ), 7.18-7.08 (m, 2H 7 and 2H 3 ), 6.75 (d, 3 J = 7.9 Hz, 2H 5 ), 6.59 (t, 3 J = 7.5 Hz, 2H6

1

  The crude mixture was diluted and washed with water, then dried over MgSO4, filtered, and evaporated under pressure. The obtained solid was dissolved in 30 mL of acetone and transferred to a pre-dried Schlenk flask under argon. Potassium carbonate 105 mg (10 eq.) was added and the reaction mixture was stirred for 5 minutes at room temperature before being heated to reflux. Then, 20 µL of diiodomethane (0.300 mmoL, 3 eq) was added and the medium further refluxed for 16 h.The reaction mixture was allowed to cool to room temperature and was diluted with EtOAc. The organic phase was then extracted with water (2 x 30 mL) and brine (1 x 30 mL), dried over anhydrous MgSO4, and the solvents evaporated under reduced pressure. The crude mixture was purified over silica gel column chromatography (n-heptane/ethyl acetate, 19:1 as eluent) to give 10 mg (25% yield) of 131 as a white solid.

	(±)-	-Methylenedioxy-	-di(1,1-dimethylethyl)-	-bis-(9-methyl-9H-carbazole) -131
		Boron tribromide (1 M in dichloromethane, 0.45 mmol, 6 eq) was slowly added to a solution
	of 131 (40 mg, 0.075 mmol) in dry dichloromethane (5 mL) at room temperature, which was stirred
	for 3 h. 1 H-NMR (400 MHz, CD2Cl2	3 J = 8.6 Hz, 2H 2 ), 7.50 (d, 3 J = 8.6 Hz, 2H 1 ), 7.31 7.29
	(m, 2H 7 , 2H 8 ), 6.89 6.72 (m, 2H 5 ), 5.70 (s, 2H 3 ), 3.96 (s, 6H 9 ), 0.66 (s, 18H 6 ).
	13 C-NMR (101 MHz, CD2Cl2		C 7 -H), 122.2, 121.9, 120.6
	(C 5 -H), 118.7 (C 1 -H), 109.2 (C 2 -H), 107.7 (C 8 -H), 104.4 (OC 3 H3), 34.3 (C-C 6 H3), 31.3 (C 6 H3), 29.8
	(N-C 9 H3).
	HR-MS Bruker MaXis 4G, ESI (+), CH3OH/CH2Cl2 (90/10); ion [M+Na] + , C35H36N2O2Na, m/z
	calculated 539.2669, m/z experimental 539.2671 (	0 ppm).
	1 H NMR (400 MHz, CD2Cl2	7.50 (d, 3 J = 8.8 Hz, 2H 2 ), 7.39 (d, 3 J = 8.8 Hz, 2H 1 ), 7.30 (dd, 3 J
	= 8.6, 5 J =2.0 Hz, 2H 7 ), 7.20 (d, 3 J = 8.5 Hz, 2H 8 ), 6.52 (d, 5 J = 2.0 Hz, 2H 5 ), 3.83 (s, 6H 9 ), 3.74
	(s, 6H 3 ), 0.97 (s, 18H 6 ).
	13 C NMR (101 MHz, CD2Cl2			C 7 -H), 122.3, 122.3, 119.9, 118.0,
	111.3 (C 1 -H), 107.8 (C 2 -H), 107.4 (C 8 -H), 57.4 (OC 3 -H3), 34.0(C-C 6 H3), 31.3 (C 6 -H3), 29.1 (N-C 9 H3).
	HR-MS Bruker MaXis 4G, ESI (+), CH3OH/CH2Cl2 (90/10); ion [M+Na] + , C36H40N2O2Na, m/z
	calculated 555.2982, m/z experimental 555.2983 (	0 ppm).

  To a pre-dried Schlenk flask, 80 mg (6 eq.) of potassium carbonate and 137(130 mg, 6 eq.) were added to a solution of 135 (87 mg, 0.13 mmol) in a mixture of 15 mL of dimethylformamide and 5 mL of water. Then, the solution was purged with argon for 15 minutes. To this pre-purged mixture, 10 mg of Pd(PPh3)4 (0.1 eq.) were added and the solution mixture was heated at 115 C for 3 h. The resulting mixture was poured into water and extracted with ethyl acetate. The combined organic phases were washed with water and brine, dried over anhydrous MgSO4, and evaporated under reduced pressure. The crude product was filtered over a silica plug and purified by recycling SEC eluting with CHCl3 to give 20 mg (19% yield) of 133.

	11,14-Bis(6-methoxy-9-methyl-9H-carbazol-3-yl)-8,17-dimethyl-8,17-dihydro-[1,3]dioxepino	[4,5-
	c:7,6-c']dicarbazole -133
	7.64 (d, 3 J = 8.7 Hz, 2H 1 ), 7.62 (d, 5 J = 2.7 Hz, 2H ), 7.52 (d, 3 J = 8.6 Hz, 2H 2 ), 7.43 (s, 2H 4 ), 7.43
	(d, 5 J = 4.2 Hz, 2H 5 ), 7.32 (d, 3 J = 8.8 Hz, 2H ), 7.17 (d, 3 J = 8.4 Hz, 2H 8 ), 7.16 7.12 (m, 2H ),
	6.64 (dd, 3 J = 8.5, 5 J = 1.8 Hz, 2H 7 ), 5.68 (s, 2H ), 4.17 (s, 6H 9 ), 4.01 (s, 6H 3 ), 3.79 (s, 6H ).
	13 C-NMR (101 MHz, CD2Cl2	146.4, 141.2, 140.4, 139.7, 136.5, 132.8, 132.7, 125.9 (C 2 -
	H), 125.4 (C 7 -H), 123.2, 122.9 (C -H), 122.8, 122.5, 121.4, 118.9 (C 2 -H), 118.2 (C 5 -H), 113.8 (C -
	1 H-NMR (400 MHz, CDCl3	s, 1H 5 ), 7.93 (dd, 3 J = 8.3, 5 J = 1.2 Hz, 1H 7 ), 7.65 (d, J =
	2.5 Hz, 1H 4 ), 7.38 (d, 3 J = 8.3 Hz, 1H 8 ), 7.32 (d, 3 J = 8.8 Hz, 1H 1 ), 7.14 (dd, 3 J = 8.8, 5 J = 2.5 Hz,
	1H 2 ), 3.93 (s, 3H 3 ), 3.81 (s, 3H 9 ), 1.43 (s, 12H 6 ).

1 H-NMR (400 MHz, CD2Cl2 3 J = 8.5 Hz, 2H ), 7.74 (dd, 3 J = 8.5, 5 J = 1.7 Hz, 2H ), H), 109.

  5 mg (0.1 eq.) of Pd(PPh3)4 were added and heated at 115 C for 3 h. The resulting mixture was poured into water and extracted with ethyl acetate. The combined organic phases were washed with water and brine, dried over anhydrous MgSO4, and evaporated under reduced pressure. The crude product was purified by silica gel chromatography (n-heptane/EtOAc, 8:2 as eluent) gave 28 mg (50% yield) of 134 as a white solid.

	1 H-NMR (400 MHz, CD2Cl2	H 4 ), 7.86 (d, 3 J = 8.6 Hz, 1H 2 ), 7.69 (s, 1H 5 ), 7.50 (d, 3 J
	= 8.5 Hz, 1H 1 ), 7.37 (d, 3 J = 8.8 Hz, 1H 8 ), 7.14 (d, 3 J = 8.9 Hz, 1H 7 ), 3.95 (s, 3H 3 ), 3.88 (s, 3H 9 ).
	13 C-NMR (101 MHz, CD2Cl2	(C 2 -H), 123.1, 118.4 (C 4 -H), 114.8
	(C 8 -H), 109.3 (C 7 -H), 108.9 (C 1 -H), 103.2 (C 5 -H), 56.0 (O-C 3 -H), 29.2 (N-C 9 -H).
	H R -M S Bruker MaXis 4G, ESI (+), CH3OH/CH2Cl2 (90/10); ion [M+Na] + , C28H24N2O2Na, m/z
	iii. Chapter 4
	2-(6-Methoxy-9-methyl-9H-carbazol-3-yl)benzaldehyde-153a
	In a dried Schlenk flask, 135 (0.35 g, 1.038 mmol), 2-formylphenyl boronic acid (0.47 g,
	3.115 mmol), K2CO3 (0.60 g, 4.15 mmol) were dissolved in a mixture of DMF (15 mL) and water
	(5 mL) under argon. The mixture was degassed by argon bubbling for 15 minutes before Pd(dppf)Cl2
	(0.1038 g, 0.07 mmol) was added and the resulting solution refluxed for 16 hours. After cooling
	down to room temperature, the reaction was poured into 20 mL of water and the organic layer was
	extracted 3 times with methylene chloride (3 × 20 mL) and thus washed with brine (20 mL) and
	dried over MgSO4. Solvents were removed under vacuum and the product was purified by silica gel
	chromatography (n-heptane/ EtOAc, 3/1 as eluent) to give 175 mg (52% yield) of 153a as a white
	solid.
	1 H-NMR (400 MHz, CD2Cl2	10.08 (s, 1H 10 ), 8.11 (d, 5 J = 1.3 Hz, 1H 4 ), 8.06 (dd, 3 J = 7.8, 5 J
	= 1.5 Hz, 1H 8 ), 7.73 (td, 3 J = 7.5, 5 J = 1.5 Hz, 1H 12 ), 7.67 7.61 (m, 1H 7 and 1H 13 ), 7.57 7.50
	(m, 1H 1 , 1H 2 , and 1H 11 ), 7.42 (d, 3 J = 8.9 Hz, 1H 14 ), 7.20 (dd, 3 J = 8.9, 5 J = 2.5 Hz, 1H 5 ), 3.95 (s,
	3H 3 ), 3.92 (s, 3H 9

  for the next step reaction. To a solution of 171 in dry dichloromethane (150 mL), boron trifluoride etherate (17 mL, BF3: 46.5%) was added, and the yellow solution turned purple immediately. After 1 h, the reaction was quenched with NaHCO3, extracted with dichloromethane, and dried by anhydrous MgSO4. The solvent was removed and the residue was purified by silica gel chromatography (heptane/CH2Cl2, 8/2 as eluent) to afford a pair of diastereomers 172 and 173.Recrystallization of the mixture of diastereomers 172 and 173 in a mixture of dichloromethane/methanol gave a diastereomer 173 in 100 mg (33%) as a white solid. J = 1.5 Hz, 1H 3 ), 7.43 (d, 5 J = 1.7 Hz, 1H 11 ), 7.37 (s, 1H ), 7.34 (d, 5 J = 1.5 Hz, 1H ), 7.28 (s, 1H 1 ), 7.22 (d, 3 J = 7.6 Hz, 1H 6 ), 7.12 7.08 (m, 1H 5 ), 7.05 (d, 5 J = 1.9 Hz, 1H ), 7.01 6.97 (m, 1H ), 6.94 (d,3 J = 7.7 Hz, 1H ), 6.63 (s, 1H ), 6.61 (s, 1H 9 ), 5.90 (s, 1H 7 ), 5.45 (s, 1H ), 4.11 (s, 3H N ), 3.09 (s, 3H 12 ), 3.03 (s, 3H 2 ), 2.73 (s, 3H ), 2.55 (s, 3H ), 2.54 (s, 3H 4 ), 2.46 (s, 3H ), 2.32 (s, 3H 8 ), 2.29 (s, 3H ), 1.12 (s, 3H ), 1.12 (s, 3H 10 ). CD2Cl2 8, 143.0, 142.9, 142.8, 142.3, 142.3, 142.1, 140.2, 137.9, 137.4, 137.2, 136.6, 136.5, 136.4, 136.3, 135.7, 135.2, 135.1, 133.5, 131.5, 130.3 (C-H 9 , C-H 9 ), 129.6 (C-H 11 ), 129.0 (C-H ), 126.5 (C-H ), 125.8 (C-H 5 ), 123.4 (C-H 6 ), 123.3 (C-H ), 123.0, 122.7 (C-H 3 ), 119.6 (C-H ), 118.0, 117.1, 112.0 (C-H 1 ), 109.5 (C-H ), 49.6 (C-H 7 ), 49.1 (C-H ), 33.2 (N-C-H), 22.4 (C-H 12 ), 22.2 (C-H 2 ), 21.7 (C-H ), 21.6 (C-H ), 21.4 (C-H 4 ), 20.6 (C-H 8 ), 20.5 (C-H ), 18.6

	Compound 172:
	1 H-NMR (400 MHz, CD2Cl2	5
		170 (220 mg, 0.48 mmol) in dry THF (50 mL)	, 2-

mesitylmagnesium bromide (1M in diethyl ether, 1.5 mL) was slowly added through a syringe. The reaction mixture was stirred for 16 h. The mixture was quenched with water, extracted with CH2Cl2, and dried by MgSO4. After removal of the solvents, the crude product of 171 was filtered over silica and used 13 C-NMR (101 MHz, (C-H ), 18.5 (C-H 10 ), 15.3 (C-H ).

  11 ), 7.39 (s, 1H ), 7.30 (s, 1H ), 7.25 (s, 1H 1 ), 7.17 (d, 3 J = 7.6 Hz, 1H 6 ), 7.09 (d, 3 J = 7.7 Hz, 1H 5 ), 7.04 (d, 5 J = 2.0 Hz, 1H ), 7.02 6.95 (m, 1H ), 6.92 (d, 3 J = 7.6 Hz, 1H ), 6.65 (s, 1H 9 ), 6.62 (s, 1H ), 5.82 (s, 1H 7 ), 5.48 (s, 1H 7 ), 4.08 (s, 3H N ), 3.03 (s, 3H 2 ), 3.02 (s, 3H 12 ), 2.73 (s, 3H ), 2.54 (s, 3H 4 , 3H ), 2.43 (s, 3H ), 2.36 (s, 3 H 8 ), 2.29 (s, 3H ), 1.18 (s, 3H ), 1.03 (s, 3H 10 ). CD2Cl2 1, 142.9, 142.8, 142.4, 142.3, 142.2, 140.1, 138.0, 137.3, 137.2, 136.6, 136.5, 136.3, 136.3, 135.6, 135.3, 135.2, 133.4, 131.5, 131.4, 130.3 (C-H 9 ), 130.2 (C-H 9 ), 129.6 (C-H 11 ), 129.0 (C-H ), 126.4 (C-H ), 125.8 (C-H 5 ), 123.3 (C-H 6 , C-H ), 123.0, 122.6 (C-H 3 ), 119.7 (C-H ), 118.0, 116.9, 112.0 (C-H 1 ), 109.4 (C-H ), 49.7 (C-H 7 ), 49.2 (C-H ), 33.2 (N-C-H), 22.4 (C-H 12 ), 22.2 (C-H 2 ), 21.8 (C-H ), 21.6 (C-H ), 21.5 (C-H 4 ), 20.6 (C-H 8 ), 20.5 (C-H ), 18.5 (C-H ), 18.4 (C-H 10 ), 15.4 (C-H ).

13 C-NMR

(101 MHz,

ray crystallographic data

	Compound	BICOL	128	129	130	131
	Empirical formula	C24H16N2O2	C28H24N2O2	C27H20N2O2	C36H40N2O2	C35H36N2O2
	CCDC number	N/A	2016849	2017143	2016850	2017144
	Formula weight (g/mol)	364.39	420.49	404.45	532.70	516.66
	Temperature	150 K	150 K	150 K	150 K	150 K
	Wavelength	0.71073	0.71073	0.71073	0.71073	0.71073
	Crystal system,	orthorhombic	triclinic	monoclinic	monoclinic	monoclinic
	space group	Pbcn	P -1	C 2/c	P 21/n	P 21/n
	a (Å)	11.1973(16)	9.5316(10)	13.408(2)	13.1390(17)	16.902(3)
	b (Å)	10.0214(13)	9.9882(11)	18.225(2)	34.437(5)	9.9528(18)
	c (Å)	15.0579(19)	12.1305(13)	7.9041(11)	13.4698(19)	17.758(2)
	(Å)	90	74.757(4)	90	90	90
	(Å)	90	77.144(4)	94.302(6)	92.046(5)	99.900(6)
	(Å)	90	74.314(4)	90	90	90
	Volume (Å 3 )	1689.7(4)	1058.4(2)	1926.0(4)	6090.8(15)	2942.8(8)
	Z	4	2	4	8	4
	Colour	colourless	colourless	colourless	colourless	yellow
	rcalculated (g.cm -3 )	1.432	1.319	1.395	1.162	1.166
	Absorption coefficient (mm -1 )	0.0092	0.083	0.089	0.071	0.072
	F(000)	760	444	848	2288	1104
	Crystal size (mm)	0.310 * 0.140 * 0.090	0.460 * 0.270 * 0.230	0.590 * 0.180 * 0.075	0.540 * 0.420 * 0.300	0.660 * 0.650 * 0.200
	range for data	2.705 to	2.169 to	3.047 to	2.208 to	2.354 to
	collection ( o )	27.533	27.604	27.484	27.550	27.519
	Tmin, Tmax	0.992, 0.781	0.858, 0.981	0.578, 0.993	0.835, 0.979	0.593, 0.986
		-14 h 14	-12 h 12	-17 h 17	-15 h 17	-21 h 21
	Limited indices	-13 k 12	-12 k 13	-23 k 21	-44 k 41	-11 k 12
		-19 l 17	-15 l 15	-10 l 10	-17 l 17	-23 l 22
	Reflections collected	9282	19999	5867	55868	23327
	Reflections unique	1910 [R(int) = 0.0673]	4856 [R(int) = 0.0527]	2216 [R(int) = 0.0834]	13753 [R(int) = 0.0647]	6630 [R(int) = 0.0735]
	Reflections [I>2sigma(I)]	1429	3871	1807	9784	4505
	Data completeness	0.976	0.987	0.996	0.979	0.981
	Absorption correction type		multi-scan
	Refinement method			Full-matrix least-squares on F 2
	Data / restraints / parameters	1910/0/133	4856/0/296	2216/0/141	13757/0/741	6630/52/383
	Goodness-of-fit	1.093	1.045	1.063	0.992	1.078
	Final R indices
	[I>2sigma(I)]

Agilent 6510, ESI (+), CH3OH/CH2Cl2 (95/5); ion [M+Na] + , C49H47NNa, m/z calculated 672.36007, m/z experimental 672.3594 1 ppm).

C. X-

  Kinetic of enantiomerization of 128 in 1,2-dichlorobenzene About 0.9 mg of the second eluted enantiomer of 128 is heated in about 15 mL of 1,2dichlorobenzene at 180°C. 20 L are taken and then injected on Chiralpak IC (90:10 heptane / 2-PrOH, 1 mL/min, UV 290 nm). The percentage decrease of the second eluted enantiomer of 128 is monitored.

				ee > 99.5%
			Chirapak IB
		Heptane / isopropanol / dichloromethane
			(90/5/5)
			RT [min]	Area	Area%
			7.94	25	0.08
			9.51	31809	99.92
			Sum	31834	100.00
			Chirapak IB
	Heptane / isopropanol / dichloromethane
			(90/5/5)
	Time (min)	% second eluted enantiomer	ln ((%t-50%)/(%(t=0)-50%))
	0		99.02	0.00000
	1422	98.18	-0.01728
	2940	97.22	-0.03741
	7583	95.31	-0.07870
	9015	93.97	-0.10872
	11561	92.99	-0.13126
				Time (minutes)
	ln ((%t-50%)/(%(t=0)-50%))	Chirapak IB Heptane / isopropanol / dichloromethane (90/5/5)
			RT [min]	Area	Area%
			7.90	4289	97.28
			9.74	120	2.72
			Sum	4409	100.00
				187

Acknowledgments

201

E. References

PMM group, Pr. Muriel Hissler and Dr.

evaluated by SQUID experiments ( EST 0.2 kcal mol -1 ). The reported findings may bring new insights on the key parameters governing the chemical and configurational stabilities of chiral organic radicals, which may offer further opportunities to design innovative organic high-spin materials.

Chapter 1 Introduction: chirality and radicals

We have successfully obtained monoradical species of both tetracarbazoles with an extended NIR absorption up to 2000 nm and found that these monoradicals have a high persistent character with half-life values up to 6.5 days under air conditions. Such high stability could be attributed to an interplay of SHI and electronic interaction from an extended conjugated bicarbazole. Moreover, the solvent polarity also tuned the electronic communication in the system, especially in 132 .

The change in UV-vis-NIR spectra when changing the solvent polarity suggested the formation of organic MV compounds class II-III. Furthermore, the solvent also impacts the ECD response for 133 . For the first time, we observed an ECD sign inversion as a function of solvent polarity.

Further investigation in diradical species provided more intense and structure UV-vis-NIR, intense NIR-5 M -1 cm -1 , and antiferromagnetic interactions evaluated by VT-EPR experiments ( ES-T 1.2 -1.4 kcal mol -1 ). The insight of the orbital arrangement revealed, for the first time, experimentally SHI in diradical 132 2 2+ with a different in SOMO energy gap 0.72 eV and co-responsible with electronic coupling between SOMO and HOMO for high stability in solution up to 220 minutes. The findings may bring further possibilities to perform chiral-induced spinselectivity (CISS) experiments and explore novel intrinsic chiral radicals with higher-spin systems.

Chapter 4

Chiral diindenocarbazole diradicals with SHI:

A possible direction towards stable chiral triradicals

This chapter is a part of publications So far, we investigated the possible decomposed product from the fluorenyl radical 161.

The solid mixture of 161 preserved at -1 H-NMR, 13 C-NMR, and LRMS after 96 h. The formation of oxidized species 164 displayed a signal in 1 H-NMR, in which the system holds its stereogenic center as observed by all the six methyl groups in the aliphatic region with a global shift to the low-field region (Figure 4

Diindenocarbazole radicals i. Synthesis and structural characterizations a) Synthesis of diindenocarbazole

In the meantime that the investigation of radicals 157 and 161, we decided to prepare helical diindenocarbazole as aza [5]helicene structure (Scheme 4-7). The synthesis of this molecule started from the preparation of 3,6-dibromo-2,7,9-trimethyl-9H-carbazole 169. More precisely, 2,7dimethyl-9H-carbazole 167 was prepared from the nitration of the -dimethylbiphenyl 165 followed by a reductive N-cyclization mediated by triphenyl-phosphine in 48% yield. [21] Then,

Conclusion and perspectives

The objectives of this Ph.D. work were focused on the development of novel chiral organic radicals and the investigation of their resulting chiroptical, photophysical, and magnetic properties.

Based on an efficient and simple synthetic strategy, fundamental aspects of radical stability were studied, offering new perspectives for the design of chiral open-shell derivatives. Such knowledge has enabled us to obtain persistent cationic and neutral chiral mono-and diradicals, which are of significant interests both in a fundamental and applied points of view due to the molecular combination of several unpaired electrons in a chiral environment. Indeed, such radicals are extremely rare, challenging to obtain, and limited to only a few systems. [1][2] Generally, the radical stabilization strategies involve by steric protection of the unpaired along with a subtle difference of electronic coupling between the two carbazole units, which is modulated by their relative dihedral angle and related to the type of chirality. Such findings thus allowed us to explore in-depth the SOMO HOMO inversion (SHI) in these molecular systems and provide new insights regarding its impact on the stability of organic radicals. The presence of the SHI in monoradicals allowed us to prepare a persistent, intrinsically chiral diradical, which notably displayed near-infrared electronic circular dichroism responses up to 1100 nm and almost degenerate singlet triplet ground states with weak antiferromagnetic interactions S-T -0.2 kcal mol -1 ) evaluated by magnetometry experiments. [3] In the second project, the question regarding the instability of unstable helical bicarbazole radicals allowed us to further investigate their dimerization. The decomposition of the monoradical 128 and unstable helical bicarbazole monoradical 129 provided evidences of oligomerization as observed by the broad NIR absorption band in the UV-vis-NIR spectroscopy, suggesting the A. General method 1 H and 13 C NMR spectra were recorded at room temperature on a Bruker AV III 400 MHz spectrometer fitted with a BBFO probe (CRMPO), Université de Rennes 1. Chemical shifts are given in ppm and coupling constants J in Hz. Chemical shifts for 1 H NMR spectra are referenced relative to residual protium in the deuterated solvent ( 1 H = 7.26 ppm, CDCl3, = 5.32 ppm, CD2Cl2, = 2.04 ppm, Acetone-d6, = 2.49 ppm, DMSO-d6). 13 C shifts are referenced to deuterated solvent ( = 77.2 ppm for CDCl3, = 53.8 ppm for CD2Cl2).

Thin-layer chromatography (TLC) was performed on aluminum sheets precoated with Merck 5735 Kieselgel 60F254. Column chromatography was carried out with Merck 5735 Kieselgel 60F (0.040-0.063 mm mesh). In order to be purified through a recycling size exclusion chromatography (SEC) apparatus, the compounds were solubilized in HPLC grade chloroform (stabilized with ethanol).

Prior to injection, the solution was filtered through a 0.45 m PTFE filter. Purification was performed on a LC-9160 II NEXT system from the Japan Analytical Industry Co., Ltd. (JAI) equipped with coupled UV-vis 4 channels NEXT through a set of two JAIGEL-2H columns at an elution rate of 10 mL•min -1 (CHCl3).

All commercial chemicals were purchased and used as received. High-resolution mass (HR-MS) determinations were performed at CRMPO on a Bruker MaXis 4G or Thermo-Fisher Q-Exactive apparatus by ASAP (+ or -) or ESI with CH2Cl2 as solvent techniques. Experimental and calculated masses are given with consideration of the mass of the electron.

Electrochemical measurements were performed with a potentiostat-galvanostat AutoLab PGSTAT 302N controlled by resident GPES (General Purpose Electrochemical System 4.9) software using a conventional single-compartment three-electrode cell. The working and auxiliary electrodes were platinum electrodes and the reference electrode was the saturated potassium chloride calomel electrode (SCE). The supporting electrolyte was 0.2 M Bu4NPF6 (tetrabutylammonium hexafluorophosphate) in dichloromethane and solutions were purged with argon before the measurements. All potentials are quoted relative to SCE.

UV-Visible/NIR (UV-vis-NIR, in M -1 •cm -1 ) absorption spectra were recorded on a Jasco V-770 spectrophotometer. Fluorescence spectra were measured on an FL 920 Edinburgh fluorimeter, while 03 integrating sphere.

Spectroelectrochemical measurements were performed with potentiostat-galvanostat Princeton by using optically transparent thin-layer electrochemical (OTTLE) cell as OMNI-cell body. The optical pathlength is ca. 0.2 cm. Enantiopure compounds were obtained from chiral HPLC platform (collaboration with N.

Vanthuyne Aix-Marseille University, Marseille, France) Optical rotations were measured on a Jasco P-2000 polarimeter with a sodium lamp (589 nm) in a 1 or 10 cm cell, thermostated at 25°C with a Peltier controlled cell holder. Specific rotations are given in 10 -1 deg•cm 2 •g -1 , and molar rotations are given in 10 -3 deg•cm 2 •mol -1 .

Electronic circular dichroism (ECD, in M -1 •cm -1 ) was measured on a Jasco J-815 Circular Dichroism Spectrometer IFR140 facility. Part of this work has been performed using the PRISM core facility (Biogenouest©, UMS Biosit, Université de Rennes 1 -Campus de Villejean-35043 Rennes Cedex, France).

The circularly polarized luminescence (CPL) measurements were performed using a home-built CPL spectrofluoropolarimeter (constructed with the help of the JASCO Company). The samples were excited using a 90° geometry with a Xenon ozone-free lamp 150 W LS. The spectra were measured with a diluted solution ca. 10 -6 M. Excitation of the samples was performed as indicated in the chapter. These following parameters were used: emission slit width 2 mm, integration time = 4 sec, scan speed = 50 nm/min, accumulations = 7.

Electron paramagnetic resonance (EPR) measurements were carried out with a Bruker 300 spectrometer (X-band, 100 kHz field modulation). Frozen solution spectra were obtained by very rapidly cooling down in a small capillary tube ( ca. 1.0 mm) the solution to avoid the formation of small crystallites.

The DC and AC magnetic susceptibility measurements were performed on solid polycrystalline samples with a Quantum Design MPMS-XL SQUID magnetometer between 2 and 300 K in an applied magnetic field of 0.2 T for temperatures of 2-20 K and 1T for temperatures of 20-300 K. constants.

B. Synthesis of compounds i. Chapter 2

3-Bromo-9H-carbazole 127, [1] 3-methoxy-9H-carbazole 115, [2] and 3-hydroxy-9H-carbazole 116 [3] were obtained according to literature procedures. 1 H-NMR analyses were in according to literatures. [1][2][3] (±)--Bis-(9H-carbazole) -BICOL [3] 2.4 g (13.1 mmol) of 3-Hydroxy-9H-carbazole 116 were dissolved in 230 mL of acetonitrile in a 250 mL round-bottom flask. Vanadyl acetylacetonate (350 mg, 10 mol%) was added and the mixture was stirred under continous bubling with a flow of ambient air at room temperature for 24 h. After that, the mixture was filtered through a short celite/silica gel plug and washed with ethyl acetate. The solvents were evaporated under reduced pressure, and the crude product was purified by column chromatography (heptane/EtOAc, 9:1 3:1 as eluent) to yield 1.3 g (55 % yield) of BICOL as a grey solid.

B. Preparation of radicals and their kinetic analysis

Preparation and recovery analysis of 130 2 2+

To a dry and degassed acetonitrile solution of 130, 2 equivalents of magic blue oxidant (EOx = 1.05 V vs SCE in acetonitrile) were added and the resulting solution was further stirred at room temperature for 5 min while its color turned to dark green (Scheme 2-11). This solution was then transferred to a dedicated cuvette for UV-vis-NIR and ECD analysis. The same procedure was performed for both enantiomers of 130.

For the SQUID experiment, 16 mg (2 eq.) of magic blue were added into an acetonitrile solution contained 5 mg (1 × 10 -4 mmol) of 130 under argon atmosphere. Then, the solution was allowed to stir and controlled by UV-vis-NIR. After full conversion to 130 2 2+ , the solution was dried under vacuum. 6.0 mg of this solid was loaded into capsules and mounted in colorless plastic straws. After the background SQUID run, magnetization for the background, Mbck, was point-bypoint subtracted from magnetization for the sample, Msample, to provide corrected magnetization, Mradical, accounting for diamagnetism of sample holder. Thus, Mradical corresponded to a mass of 3.3 mg.

Recovery analysis of 130 2 2+

To a solution of BICOL derivatives 130 (5 mg, 9.39 M) in 10 mL acetonitrile (MeCN) under argon atmosphere, 16.2 mg of magic blue (2.1 equivalent) were added and the solution was stirred for 10 minutes under argon atmosphere to ensure full conversion. Then, the solution was quenched by the addition of Na2S2O3 ged from dark green to yellow. The solution was evaporated under reduced pressure and purified by column chromatography (SiO2, pentane/CH2Cl2, 1:1) to obtain a white powder of 130 (4.0 mg, 80% recovery), which was confirmed by 1 H NMR analysis (400 MHz, CD2Cl2). Since the NMR of the crude reaction shows only starting material 130 and reduced magic blue oxidant, and no presence of other side products, it is reasonable to say that the loss of 1 mg occurred during the purification step (and not from a possible degradation of 130 2 2+ ).

UV-vis titration studies

Oxidation process in dichloromethane were studied by UV-vis-NIR spectroscopy at 298 K.

Solution of each molecule (10 -5 M) was prepared using dry-dichloromethane as a solvent. Increasing number of (4-BrPh)3NSbCl6 (so-called magic blue, EOx = 1.16 V vs SCE) [16] equivalents were added to the separate vials under argon (3.0 mL in a 1 cmconcentration was kept constant.

Oxidation of 128 + , 130 + , and 130b +

Generation of monooxidized-species in dichloromethane were studied by UV-vis-NIR spectroscopy at 298 K. Solution of each molecule (10 -5 M) was prepared using dry-dichloromethane as a solvent. The excess amount of AgBF4 (EOx = 1.11 V vs SCE) [16] equivalents was added to the vials under either argon of air (3.0 mL in a 1 cm-pathlength quartz cell). Then, the compound was All radical species in this analysis were prepared according to the described procedure and added directly to the separated cuvettes under argon or air atmosphere. After measurement of monoradical, the sample was reduced by Na2S2O3 -resolution mass spectrometry (LRMS) using dithranol as a matrix carrier. For 130 2 2+ , a specific procedure will be described in its corresponding section.

Kinetic analysis of 132 + , 133 + , and 134 +

Oxidation process in either dichloromethane or acetonitrile were studied by UV-vis-NIR spectroscopy at 298 K. Solution of each molecule (10 -5 M) was prepared using dry-dichloromethane or degassed-acetonitrile as a solvent. An exact amount of (4-BrPh)3NSbCl6 (so-called magic blue, EOx = 1.16 V (CH2Cl2) and 1.05 V (MeCN) vs SCE) [16] equivalents was added to the separate vials under ambient (for monoradical) and under argon (for diradical, 3.0 mL in a 1 cm-pathlength quartz cell). The concentration of bicarbazole and tetracarbazole derivatives was kept constant.

General procedure for dehydrogenative-oxidation of indenocarbazole derivatives [17] Under argon atmosphere and in the dark, the hydrogenated compound (0.10 eq.) was dissolved in dry THF (4 ml). Then, t-BuOK (2.0 eq.) was added with the solution becoming dark red colored immediately. The solution was stirred for 1.5 h in the dark at room temperature; then p-chloranil (2.7 eq.) was added and continued stirring for 2 h. After completion of the reaction, the solvent was removed under vacuum and the crude product was purified by silica gel column chromatography (petroleum ether/CH2Cl2, 2:1 as eluent). The crude products were used without further purification.

D. Chiral HPLC separation and analysis

These chiral separations and analyses were performed by Dr. Nicolar Vanthuyne and co-workers (Aix-Marseille University, France).

Analytical chiral HPLC separation for compound 128

and detected with a UV detector at 230 nm and a circular dichroism detector at 254 nm. The flow rate is 1 mL/min. Semi-preparative separation for compound 133:

133 are dissolved in 20 mL of dichloromethane. S,S)-Whelk-O1 (250 x 10 mm), ethanol / dichloromethane (50/50) as mobile phase, flow-rate = 5 mL/min, UV detection at 254 nm.

L, every 7.7 minutes. Preparative purification for compound 172+173:

172+173 are dissolved in 3 mL of a mixture of dichloromethane and hexane (50/50).

Chromatographic conditions: (S,S)-Whelk-O1 (250 x 10 mm), hexane / dichloromethane (80/20) as mobile phase, flow-rate = 5 mL/min, UV detection at 254 nm.

L, every 9.5 minutes. 172, then separated on another column) Abstract : Chiral -conjugated materials have recently emerged as a promising direction in materials science due to their specific interaction with circularly polarized light and the potential of the latter in several domains of applications such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and magnets. While extensive researches have been focusing on organic chiral dyes with closed-shell electronic configuration, few attentions have been paid on their open-shell counterparts (radicals), presumably because of their reactivity and stability issues. This thesis has aimed to develop novel intrinsic chiral radicals based-on carbazole moiety. We explored a new molecular design of persistent intrinsically chiral organic radicals via a SOMO-HOMO level inversion (SHI) process. This electronic configuration allowed us to highlight certain key parameters governing the stability of the obtained radical species. We have extended this approach to various cationic and neutral radical structures, resulting in the generation of novel and relatively stable cationic and neutral chiral mono-and di-radicals, presenting both fundamental and promising directions in optoelectronic applications.