-Qin Wang

Hirosato Monobe
email: monobe-hirosato@aist.go.jp

Bertrand Donnio
email: bertrand.donnio@ipcms.unistra.fr

Wen-Jing Deng

Shuai Liu

Hang Lin

Ke-Xiao Zhao
email: kqzhao@sicnu.edu.cn

Xiao-Yan Bai

Ke-Qing Zhao

Ping Hu

Bi-Qin Wang

Ditriphenylenothiophene butterfly-shape liquid crystals. The influence of polyarene core topology on self-organization, fluorescence and photoconductivity

Ditriphenylenothiophene butterfly-shape liquid crystals.

The influence of polyarene core topology on self-organization, fluorescence and photoconductivity

Introduction

The concerted design of organic semiconducting and luminescent liquid crystals (LCs) has attracted a lot of attention in the last two decades due to their great potential for applications in optoelectronics. The development of the corresponding technologies mainly relies on methodical molecular approaches, based on both highly creative molecular design and systematic advances in the chemistry of π-conjugated systems. 1,[START_REF] Coropceanu | Charge Transport in Organic Semiconductors[END_REF] The crucial parameter for the evaluation of the performance of organic semiconducting materials is the charge carrier mobility rate (μ), which is typically governed by intermolecular orbital overlaps. Thus, the importance of precisely controlling such intermolecular interactions is to achieve effective charge-transport properties. Research in this domain has primarily focused on synthesizing large π-extended polycyclic heteroaromatic hydrocarbons (PAHs) to maximize molecular orbital overlaps to improve intermolecular interactions and their electronic/optical/physical properties, and for instance, charge transport efficacy. [START_REF] Stępień | Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications[END_REF] In this effort, the main fabrication strategy consists of the stepwise connection of different types of π-conjugated fragments together through various functional groups in order to extend the π-conjugated core system. 4- 7 An underlying consequence of this molecular strategy is the possibility to modulate further and very precisely the electronic coupling between these different building blocks by simply modifying the mutual orientation, position and/or arrangement of these groups and/or their linkages. The latter molecular concept based on positional isomerism has been advantageously and is being increasingly used in the design of many new families of organic chromophores and semiconductors. [START_REF] Poriel | Dihydroindenofluorene Positional Isomers[END_REF] Another compelling approach in this field of research consists of the grafting of aliphatic chains in the periphery of these polyaromatic systems. [START_REF] Watson | Big Is Beautiful-"Aromaticity" Revisited from the Viewpoint of Macromolecular and Supramolecular Benzene Chemistry[END_REF] The presence of these paraffinic chains not only improves their solubility and ease of device fabrication through low-cost solution-processing techniques, but also plays a crucial role in inducing anisotropic ordered molecular self-assemblies (liquid crystals) and thin films with a long-range structured morphology in order to optimize intermolecular interactions in specific directions and over sufficiently long ranges. The phase segregation occurring at the molecular level between the various immiscible molecular parts, i.e. chains and π-conjugated cores, indeed leads to ordered nanostructures which favor charge transfer in specific directions, whilst limiting this effect in other directions. [START_REF] Feng | Towards high charge-carrier mobilities by rational design of the shape and periphery of discotics[END_REF] Among the widely studied rod-like luminescent and semiconducting liquid crystals, thiophene-containing systems usually show outstanding performances, with large μ values 10- 15 and fine device properties. [START_REF] Shimizu | Mesophase semiconductors in field effect transistors[END_REF] Numerous structure-property relationship studies revealed that the expansion of sulfur atomic orbitals in π-conjugated polyaromatics is beneficial for more efficient intermolecular π-π orbital overlap and stronger π-π and sulfur-sulfur interactions between the molecules and the highly ordered lamellar architectures of the liquid crystals, enlarging the intermolecular electron hopping rates (μ). With such studies, thiophene has been proved to be an indispensable building block for two-dimensional semiconductors based on smectic phases. [START_REF] Kato | Transport of Ions and Electrons in Nanostructured Liquid Crystals[END_REF] Similarly, thiophene-fused discotic liquid crystals (DLCs) [START_REF] Kumar | Recent developments in the chemistry of triphenylene-based discotic liquid crystals[END_REF][START_REF] Sergeyev | Discotic liquid crystals: a new generation of organic semiconductors[END_REF][START_REF] Kaafarani | Discotic Liquid Crystals for Opto-Electronic Applications[END_REF][START_REF] Wöhrle | Discotic Liquid Crystals[END_REF][START_REF] Yuan | From S,N-Heteroacene to Large Discotic Polycyclic Aromatic Hydrocarbons (PAHs): Liquid Crystal versus Plastic Crystalline Materials with Tunable Mechanochromic Fluorescence[END_REF][START_REF] Kwon | Charge Transportation and Chirality in Liquid Crystalline Helical Network Phases of Achiral BTBT-Derived Polycatenar Molecules[END_REF][START_REF] Ghosh | Liquid crystals from shape-persistent porphyrin stars with intrinsic free space[END_REF][START_REF] Cabral | Columnar Liquid-Crystalline Dibenzopentacenodithiophenes by Photocyclization[END_REF][START_REF] Gan | Guanine-oligothiophene conjugates: liquid-crystalline properties, photoconductivities and ion-responsive emission of their nanoscale assemblies[END_REF][START_REF] Tober | Tris(5-aryl-1,3,4-oxadiazolyl)benzotrithiophenes -Discotic Liquid Crystals with Enormous Mesophase Ranges[END_REF][START_REF] Taing | 1,3,5-Triazine(trithiophenylcarboxylate) esters form metastable monotropic nematic discotic liquid crystal phases[END_REF][START_REF] Bala | High hole mobility in room temperature discotic liquid crystalline tetrathienoanthracenes[END_REF][START_REF] Hu | An Electric-Field-Responsive Discotic Liquid-Crystalline Hexa-peri-Hexabenzocoronene/Oligothiophene Hybrid[END_REF][START_REF] Zhang | Discotic Triphenylene Twins Linked through Thiophene Bridges: Controlling Nematic Behavior in an Intriguing Class of Functional Organic Materials[END_REF][START_REF] Xiao | Propeller-Shaped Fused Oligothiophenes: A Remarkable Effect of the Topology of Sulfur Atoms on Columnar Stacking[END_REF][START_REF] Li | Thiophene-fused polyaromatics: synthesis, columnar liquid crystal, fluorescence and electrochemical properties[END_REF][START_REF] Suzuki | Topological Control of Columnar Stacking Made of Liquid-Crystalline Thiophene-Fused Metallonaphthalocyanines[END_REF][START_REF] Dang | Isomeric organic semiconductors containing fusedthiophene cores: molecular packing and charge transport[END_REF] consisting of a π-extended polyaromatic core surrounded by peripheral alkyl chains also display remarkable assets: they spontaneously self-organize into stable columnar mesophases and show unidimensional μ values ranging from 10 -4 up to 10 -2 cm 2 V -1 s -1 . [START_REF] Kwon | Charge Transportation and Chirality in Liquid Crystalline Helical Network Phases of Achiral BTBT-Derived Polycatenar Molecules[END_REF][START_REF] Zhao | Boardlike Fused-Thiophene Liquid Crystals and their Benzene Analogs: Facile Synthesis, Self-Assembly, p-Type Semiconductivity, and Photoluminescence[END_REF][START_REF] Liu | Molecular design of benzothienobenzothiophene-cored columnar mesogens: facile synthesis, mesomorphism, and charge carrier mobility[END_REF][START_REF] Ma | Nonlinear Nonacenes with a Dithienothiophene Substructure: Multifunctional Compounds that Act as Columnar Mesogens, Luminophores, π Gelators, and p-Type Semiconductors[END_REF][START_REF] Ma | Butterfly-like Shape Liquid Crystals Based Fused-Thiophene as Unidimensional Ambipolar Organic Semiconductors with High Mobility[END_REF] While developing such DLC-based semiconducting systems, various strategies, including, notably, the extension of πconjugated polyaromatic cores, [START_REF] Bushby | Liquid Crystalline Semiconductors[END_REF][START_REF] Schmidt-Mende | Self-Organized Discotic Liquid Crystals for High-Efficiency Organic Photovoltaics[END_REF] molecular dynamic motion controlled by intermolecular hydrogen-bonding, [START_REF] Demenev | Quasi Temperature Independent Electron Mobility in Hexagonal Columnar Mesophases of an H-Bonded Benzotristhiophene Derivative[END_REF][START_REF] Paraschiv | H-Bond-Stabilized Triphenylene-Based Columnar Discotic Liquid Crystals[END_REF] and nanosegregation by hydrophilic/hydrophobic 6 and fluorophilic/fluorophobic interactions, [START_REF] Sosa-Vargas | Liquid crystalline and charge transport properties of novel non-peripherally octasubstituted perfluoroalkylated phthalocyanines[END_REF] have been largely considered and successfully applied to promote and enhance charge carrier mobility. Despite numerous studies, the effect of positional/regio-isomerism on the physical properties of sulfur-containing π-conjugated disc-like polyaromatics has been rarely investigated to date. [START_REF] Xiao | Propeller-Shaped Fused Oligothiophenes: A Remarkable Effect of the Topology of Sulfur Atoms on Columnar Stacking[END_REF][START_REF] Li | Thiophene-fused polyaromatics: synthesis, columnar liquid crystal, fluorescence and electrochemical properties[END_REF][START_REF] Suzuki | Topological Control of Columnar Stacking Made of Liquid-Crystalline Thiophene-Fused Metallonaphthalocyanines[END_REF][START_REF] Dang | Isomeric organic semiconductors containing fusedthiophene cores: molecular packing and charge transport[END_REF] For some polycyclic thiophene-fused DLCs reported, not only the mesomorphous properties (phase type, temperature ranges, and transition temperatures) and air/thermal/photo/chemical stabilities, but also the fluorescence behavior and photoconductivity/device performances were found to be strongly controlled by the relative orientations of the sulfur atoms, which also significantly alter π-π stacking and sulfur-involved intermolecular interactions between isomers. Investigation of the molecular isomerism of thiophene-based DLCs therefore appears as an important and inevitable step in the development of organic-based electronic and optoelectronic devices with optimized performances.

Chart 1 Various thiophene-containing butterfly-shaped columnar liquid crystalline semiconductors synthesized by Suzuki-Miyaura cross-coupling (blue bonds) and Scholl oxidative (red bonds) reactions tandem (DT, 34 BTBT, [START_REF] Liu | Molecular design of benzothienobenzothiophene-cored columnar mesogens: facile synthesis, mesomorphism, and charge carrier mobility[END_REF] DTT, 36 CDTO, 37 DTPTB and DTPTA, this work).

Herein, we report the design and facile synthesis of two series of isomeric butterfly-shaped mesogens based on a dibenzothiophene core fused with triphenylene wings, namely α,β-and β,β-fused ditriphenylenothiophene, DTPTA and DTPTB, respectively (Chart 1), equipped with eight long peripheral alkoxy chains, by the Suzuki-Miyaura coupling/Scholl oxidative cyclization reaction combination. Their self-organizational behavior, organic solvent gelling properties, UV-vis absorption and fluorescence emission in solution and in the solid state, light-induced charge carrier mobility measured by the time-of-flight (TOF) method are reported, and discussed in relation to their molecular structures.

Results and discussion

Synthetic procedures and characterization. Based on the recently developed synthesis of (tetraalkoxy)biphenyl-Br/biphenyl-Bpin building blocks, [START_REF] Hang | Butterfly Mesogens Based on Carbazole, Fluorene or Fluorenone: Mesomorphous, Gelling, Photophysical, and Photoconductive Properties[END_REF][START_REF] Ramakrishna | Conveniently Synthesized Butterfly-Shaped Bitriphenylenes and their Application in Solution-Processed Organic Field-Effect Transistor Devices[END_REF] various butterfly-shaped πconjugated molecules (see Chart 1 for some thiophene-containing representative examples) can be synthesized in two steps by Pd-catalyzed Suzuki-Miyaura coupling [START_REF] Miyaura | Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds[END_REF][START_REF] Suzuki | Cross-Coupling Reactions Of Organoboranes: An Easy Way To Construct C-C Bonds (Nobel Lecture)[END_REF][START_REF] Sarhan | Iron(III) chloride in oxidative C-C coupling reactions[END_REF] and FeCl3promoted Scholl cyclo-dehydrogenation reactions tandem. [START_REF] Grzybowski | Comparison of Oxidative Aromatic Coupling and the Scholl Reaction[END_REF][START_REF] Grzybowski | Synthetic Applications of Oxidative Aromatic Coupling-From Biphenols to Nanographenes[END_REF][START_REF] Zhao | Facile transformation of 1-aryltriphenylenes into dibenzo[fg,op]tetracenes by intramolecular Scholl cyclodehydrogenation: synthesis, self-assembly, and charge carrier mobility of large π-extended discogens[END_REF][START_REF] Zhao | Design of Janus triphenylene mesogens: Facile synthesis, mesomorphism, photoluminescence, and semiconductivity[END_REF][START_REF] Myśliwiec | Peripherally Fused Porphyrins via the Scholl Reaction: Synthesis, Self-Assembly, and Mesomorphism[END_REF][START_REF] Dai | Liquid crystal ionic self-assembly and anionselective photoluminescence in discotic azatriphenylenes[END_REF][START_REF] Oyama | High-Mobility Regioisomeric Thieno[END_REF] Here, di-and tetrabromodibenzothiophenes [START_REF] Donnio | A Generalized Model for the Molecular Arrangement in the Columnar Mesophases of Polycatenar Mesogens. Crystal and Molecular Structure of Two Hexacatenar Mesogens[END_REF] were used as starting reagents, and coupled with biphenyl-2-boronic and phenylboronic ester building blocks (Schemes S1 and S3, ESI †), respectively, to yield the two sets of isomeric tetraphenyldibenzothiophenes, Dn and Tn. The two corresponding fused isomeric butterfly-shaped ditriphenylenothiophene derivatives, DTPTAn and DTPTBn, were readily accessible by Scholl cyclodehydrogenation (Scheme 1). In brief, 2,3,7,8-tetrabromodibenzo [b,d]thiophene [START_REF] Donnio | A Generalized Model for the Molecular Arrangement in the Columnar Mesophases of Polycatenar Mesogens. Crystal and Molecular Structure of Two Hexacatenar Mesogens[END_REF] was reacted with 2-(3,4bis(alkoxy)phenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, and 4,6dibromodibenzo [b,d]thiophene was reacted with 4,4,5,5-tetramethyl-2-(3′,4,4′,5tetrakis(alkoxy)-[1,1′-biphenyl]-2-yl)-1,3,2-dioxaborolane by Pd catalyzed Suzuki-Miyaura cross-coupling to give intermediates Tn (n = 12, 14, 16) and Dn (n = 8, 10, 12), respectively, in high yields (>80%). Subsequently, Scholl oxidative cyclodehydrogenation by FeCl3 generated the corresponding homologous fused DTPTBn and DTPTAn compounds. It is worth noting that a primary study showed that DTPTBn displayed high phase transition temperatures and so compounds with longer alkoxy chains were synthesized (n = 12, 14, 16) in order to decrease the temperatures; in contrast, since DTPTAn isomers showed low phase transition temperatures, only short-chain homologues were synthesized (n = 12, 10, 8). Both regioisomers with the same chain-lengths, DTPTB12 and DTPTA12, were synthesized for a direct comparison. DTPTBn compounds were purified using a basic alumina (Al2O3) chromatography column as they are prone to decay on an acidic silica gel chromatography column, and obtained in only ca. 60% yields. DTPTAn compounds were synthesized in short reaction times and obtained with high yields (ca. 80%). All the butterfly-shaped molecules were fully characterized by 1 H NMR, [START_REF] Oikawa | High Carrier Mobility of Organic Field-Effect Transistors with a Thiophene-Naphthalene Mesomorphic Semiconductor[END_REF] C NMR, EA and HRMS (Fig. S10 and S11, ESI †); [START_REF] Oikawa | High Carrier Mobility of Organic Field-Effect Transistors with a Thiophene-Naphthalene Mesomorphic Semiconductor[END_REF] C NMR spectra could not be recorded for DTPTBn due to their tendency to aggregate in solvent. The results were in good agreement with the expected chemical structures.

Thermal stability (TGA) and mesomorphic properties (DSC, POM, S/WAXS).

The high thermal stability of semiconducting organic materials is essential for device fabrication by vapor phase deposition and improving order by thermal annealing. Prior to the careful analysis of the liquid crystalline properties, we evaluated the thermal stability of the precursors Dn and Tn, and the corresponding cyclized DTPTBn and DTPTAn compounds by thermogravimetric analysis (TGA) in dynamic mode (see Fig. S1 in the ESI † for details). All compounds showed high thermal stability, with decomposition temperatures (measured at 5% weight loss) in the same range above ca. 360 °C, and almost not affected by the core topology (Dn vs.Tn, Dn vs.DTPTAn, Tn vs.DTPTBn, and DTPTAn vs.DTPTBn) or by the alkyl chain length (n = 8, 10, 12, 14, 16, Tables S1 andS2, ESI †).

The mesomorphic properties of the intermediates and target compounds were first investigated by polarizing optical microscopy (POM, Fig. 1 and Fig. S2, ESI †) and differential scanning calorimetry (DSC, Fig. S3, ESI †). Except for the non-mesomorphous Dn precursors (Table S3, ESI †), all Tn, DTPTBn and DTPTAn derivatives exhibited enantiotropic LC phases; T16 was found to be monotropic (mesophase induced on cooling only). As the samples were slowly cooled from the isotropic liquid, typical fan-shaped textures were observed for Tn and DTPTBn, while long linear defects and large homeotropic zones, demonstrating their strongly homeotropic alignment behaviour (ordered face-to-face columnar stacks on an untreated glass substrate, with a perpendicular column axis), were observed for DTPTAn. All polarized optical textures supported the characteristic features of columnar mesophases (Fig. 1 and Fig. S2, ESI †). Overall, upon increasing the alkoxy chain length, the isotropisation temperatures (Cr → Iso for Dn, or Col → Iso for the other compounds) decreased smoothly for all compounds (Fig. 2 and Fig. S3, ESI †). For both precursors, isotropisation temperatures are systematically higher for Tn than for Dn. For the mesomorphous precursors, the mesophase ranges narrowed rapidly from T12 to T14, to completely disappeared for T16; T12 thus exhibits the widest mesophase range of ca. 59 °C, covering room temperature (Fig. S3, ESI †). For DTPTBn, the mesophase ranges were obviously widened due to the fused peripheral benzene rings and the consequent enlargement and extension of the π-conjugated system of the central ditriphenylenothiophene core (Fig. 2). The clearing temperatures of DTPTBn were all higher than 200 °C, and the highest one was for DTPTB12, up to 240 °C. Mesomorphism was induced in the DTPTAn compounds in agreement with π-conjugation extension and flattening of the core. Compared with DTPTBn, the clearing points of DTPTAn were much lower and the mesophase ranges were consequently also narrower. The highest clearing point, 193 °C, and the largest mesophase range, 126 °C, were found for DTPTA8. In contrast, the melting points (Cr → Col) of DTPTAn and DTPTBn lie in the same range (86-89 °C, except for DTPTA12, 70 °C, Table S4, ESI †). The difference of the mesophase ranges is a priori attributed to the core architecture and planarity, as seen below.

The nature of the mesophases and supramolecular organizations of these butterfly-shaped ditriphenylenes, DTPTBn and DTPTAn, and precursors Tn, was deduced from small-and wideangle X-ray scattering (S/WAXS, Fig. 3 and Fig. S4, Table S5, ESI †) and the main geometrical data are summarized in Table 1. ). d Columnar slice thickness, hmol = Vmol/A (Å), and stacking distance, hπ (Å), average π-π stacking distance between molecules determined from the S/WAXS pattern, and ξ: correlation length (Å), determined by the Debye-Scherrer formula. e Out-of-plane tilt angle of mesogen cores inside columns (°), ψ = arcos(hπ/hmol). f Aromatic volume fraction, χcore = Var/Vmol, with Var ≈ 625 Å 3 . g Diameter (Å) of equivalent circular cross-sectional area Acore, Dcyl = √(4 × Acore/π), with Acore = χcoreA. h Cylinder area per chain, Sch = πDcyl × hmol/nch (Å 2 ), where nch is the number of chains per molecule, i.e. nch = 8. i Chain packing ratio, q = Sch/σch, where σch (Å 2 ) is the cross-sectional area of a molten chain (σCH2 = VCH2/1.27).

In all cases, the S/WAXS patterns possess the characteristic features of liquid-crystalline phases with sharp, small-angle reflections emerging from nanosegregated structures formed by the antagonistic aromatic and aliphatic segments, along with the two scattering signals in the wide-angle region, hch and hπ, arising, respectively, from liquid-like lateral distances between molten chains (hch) and from the stacking between successive mesogenic cores (hπ). The assignment of the Colhex mesophase was unambiguously confirmed by S/WAXS for the Tn and DTPTBn compounds, with the presence of one sharp and very intense first-order reflection (indexed as 10), along with additional weaker higher-order reflections, indexed as (11), (20), and ( 21) or (30) for Tn and ( 11) and (20) for DTPTBn, respectively (Table S5, ESI †), according to the sequence of squared spacing ratios 1 : √3 : 2 : √7 (or 3), confirming the longrange ordering of a two-dimensional hexagonal lattice. The S/WAXS patterns of DTPTAn only displayed one single and intense small-angle reflection making its assignment ambiguous. However, supported by characteristic optical textures (POM, Fig. 1 and Fig. S2, ESI †), this reflection was nevertheless associated with the fundamental reflection (10) of a Colhex mesophase. The wide-angle parts for both isomers consisted of a broad double-peak corresponding to molten chains and π-stacking, respectively. The signal corresponding to the core-core stacking is, however, significantly more intense and of longer range for DTPTBn compounds than for DTPTAn ones (Fig. 3 and Fig. S4, Table S5, ESI †), suggesting a slightly more efficient and correlated stacking for the former. As for the Tn compounds, the four phenyl groups connected to the central rigid dibenzothiophene core via simple σ bonds can rotate freely (DFT, Fig. 4), thus hindering perfect core-core stacking, and consequently giving rise to a single large scattering signal for the undifferentiated contribution of both alkyl chains and cores, except for T16, for which a very intense peak could emerge from the broad scattering, suggesting a long-range π-π stacking correlation. For DTPTB12, an additional transition was detected by DSC, at about 132 °C on heating, and fully reversible (ca 110 °C) on cooling, between the crystalline phase and the upper Colhex mesophase. However, no difference could be made neither by POM (Fig. S2b,ESI †) nor by S/WAXS between this mesophase and the Colhex phase just above, which suggests the formation of a second Colhex phase (here referred to as Col'hex). The differentiation between both mesophases could only be made on the intensity variation of the WAXS signal corresponding to the disc stacking, hπ, which increases in the Col'hex mesophase i.e. the extension of the order-range of the core stacking (Fig. 3, hπ), possibly due to an a priori more regular molecular stacking (see below).

As shown by DFT calculations (Fig. 4) on the homologous methoxy derivatives, DTPTA1 and DTPTB1, the π-conjugated cores of these isomers have a different topology, as expected. The close proximity of the aliphatic chains near the congested cavity (where the sulfur atom of the thiophene fragment is hidden by two triphenylene side-arms and chains) of DTPTA1 produces out-of-plane steric distortions of the π-conjugated core, further reducing substantially the efficiency of the orbital overlaps, likely detrimental to perfect stacking. In contrast, DTPTB1 remains perfectly flat, since the triphenylene side-arms lie further apart, and consequently, the chains are more homogeneously distributed around the core, in agreement with an easier stacking along the columnar axis, similarly to other structurally related butterfly-shaped mesogens. [START_REF] Zhao | Boardlike Fused-Thiophene Liquid Crystals and their Benzene Analogs: Facile Synthesis, Self-Assembly, p-Type Semiconductivity, and Photoluminescence[END_REF][START_REF] Liu | Molecular design of benzothienobenzothiophene-cored columnar mesogens: facile synthesis, mesomorphism, and charge carrier mobility[END_REF][START_REF] Ma | Nonlinear Nonacenes with a Dithienothiophene Substructure: Multifunctional Compounds that Act as Columnar Mesogens, Luminophores, π Gelators, and p-Type Semiconductors[END_REF][START_REF] Ma | Butterfly-like Shape Liquid Crystals Based Fused-Thiophene as Unidimensional Ambipolar Organic Semiconductors with High Mobility[END_REF] The emergence of the hexagonal symmetry implies that the columns are localized at the nodes of the hexagonal network, and that they must have an average circular cross-section allowing the homogeneous distribution of the aliphatic chains around the columns in an infinite continuum. Unlike classical discotic mesogens with a high degree of rotational symmetry such as triphenylenes, the rigid aromatic cores of both DTPT α/β-isomers are not discoidal, as revealed by DFT calculations (Fig. 4), and moreover, both mesogens have a bald side with less aliphatic chains, suggesting that a chain compensation mechanism is at work to overcome this deficiency, likely involving primarily the neighboring mesogens from above and below. The core/chain interface, defined by the segregation between the immiscible parts, can take the shape of a cylinder if the molecules stack on top of each other with antiparallel stacking and a continuous change of orientation of their long molecular axis between the neighboring pseudo-ellipsoidal molecules (Fig. 5), [START_REF] Zhao | Boardlike Fused-Thiophene Liquid Crystals and their Benzene Analogs: Facile Synthesis, Self-Assembly, p-Type Semiconductivity, and Photoluminescence[END_REF][START_REF] Liu | Molecular design of benzothienobenzothiophene-cored columnar mesogens: facile synthesis, mesomorphism, and charge carrier mobility[END_REF][START_REF] Ma | Nonlinear Nonacenes with a Dithienothiophene Substructure: Multifunctional Compounds that Act as Columnar Mesogens, Luminophores, π Gelators, and p-Type Semiconductors[END_REF][START_REF] Ma | Butterfly-like Shape Liquid Crystals Based Fused-Thiophene as Unidimensional Ambipolar Organic Semiconductors with High Mobility[END_REF] to generate columns of nearly average circular cross-section (whose resulting equivalent circular cross-sectional diameter can be approximated to Dcyl, Table 1). This alternated piling, which may somehow resemble at first that of a helicoidal stacking, is necessarily driven by the reduced density of chains around one side of the dibenzothiophene segment, leading to this compensating mechanism, but unlike for helicoidal columns, this stacking is not concerted, and random changes of the molecular orientations with respect to the columnar axis are likely to occur (Fig. 5, middle). This associative mechanism finally results in the even distribution of chains around the supramolecular columnar cores, as in polycatenar systems. [START_REF] Voskuhl | Mesogens with aggregation-induced emission properties: Materials with a bright future[END_REF] The deficiency of chains is also regulated by the neighboring columns through the aliphatic continuum. If necessary, additional tilting of the cores, ψ, relative to the lattice plane, along the stacking direction, can also take place in order to fully accommodate the chain interface. In all cases, the surface area required for the peripheral chains was found to be greatly compatible with the interface area offered by these π-conjugated core stacks, as evidenced by the ratio q 53 (Table 1) which does not deviate much from unity (maximum deviation of less than 7% for DTPTB compounds, and less than 5% for DTPTA compounds). The chains are therefore stretched and densely packed, which allows easy orientational changes between the neighboring molecules within the same column, as discussed above, and, obviously, between the columns, and hence the homogeneous and dense distribution of the aliphatic chains at their periphery. The values of molecular slice thicknesses, hmol, deduced from the ratio of the molecular volume to columnar surface area for all compounds, are slightly larger than hπ (Table 1), which can be interpreted to a slightly tilted stacking (10 < ψ < 30°) of the mesogenic cores along the columnar axis for DTPTB compounds, and to the deviation from flatness for the DTPTA homologs. A schematic model of the supramolecular organization is proposed in Fig. 5. These models (Fig. 5) are consistent with the high mesophase stability observed in these series of compounds, and explain the difference in stability between the two regio-isomers in their ability to propagate the long-range ordered stacking and maintain column cohesion in the mesophase. DFT calculations of model compounds T1 and D1 (Fig. 4) for precursors are also fully consistent with the reduction of the mesophase stability for Tn, or by the lack of mesomorphism in Dn derivatives.

Photophysical properties

As mentioned earlier, the design of fluorescent liquid crystalline materials is an interesting research subject for the numerous potential applications they offer in various fields (in optical sensing and detection, as probes, or optoelectronic displays). [START_REF] Babu | Functional π-Gelators and Their Applications[END_REF] S-Containing hetero-aromatics usually have outstanding optical properties. The photophysical properties of these new compounds were studied by UV-vis absorption in solution and fluorescence emission in both solution and thin film states (Fig. 6) and DFT calculations performed. The detailed parameters are gathered in Table 2. a Absorption (λabs) and emission (λem) wavelengths in nm; molecular absorption coefficient (ε × 10 4 , L mol -1 cm -1 ); QY, absolute quantum yields (%) measured in THF solutions at a concentration of 1 × 10 -5 mol L -1 (see excitation wavelengths in the caption to Fig. 6).

In the UV-vis spectra, Tn compounds have a wide absorption band containing two main absorption peaks (280-282 and 326 nm, Fig. 6a), which can be attributed to the intramolecular electronic transition from the lower energy occupied molecular orbitals to higher energy unoccupied molecular orbitals of the π-conjugated core. Dn compounds also present a wide absorption band containing three absorption peaks (242, 292 nm and an additional weak band at 326 nm, Fig. 6a). As was expected, Dn showed different absorption spectra from the Tn derivatives (band at 242 nm essentially) because of the changing environment around the dibenzothiophene core. DTPTBn compounds have their maximum absorption at 298 nm, which is attributed to the di-triphenylene nuclei with π-conjugated extension, and also the absorption peaks at 258 nm and 378 nm (Fig. 6d); the additional absorption band at 325 nm would, according to the DFT calculation (ESI † part, Fig. S9 and Table S3), likely come from the excitation of HOMO-1 to the LUMO and HOMO-2 to the LUMO. DTPTAn isomers have their maximum absorption at 304 nm, which is also attributed to the double triphenylene part of the π-conjugated extension. In addition, there are three smaller absorption peaks of the same and weaker intensity at 352 nm, 370 nm and 384 nm. These values showed that due to the extension of the π-conjugated system, the absorption spectra of DTPTBn and DTPTAn were red-shifted and their intensity increased. By comparing the strongest absorption peaks of DTPTAn and DTPTBn, the small red shift of DTPTAn (≈6 nm) indicated that the position of annulation on the ditriphenylenothiophene nucleus have a certain influence on the electronic structure. In other words, the βsubstituted DTPTBn absorbed light at relatively shorter wavelengths than the αsubstituted DTPTAn ones, likely caused by the distorted nuclear core, and thus lowered the molecular symmetry and split molecular orbitals.

All Tn, Dn, DTPTBn and DTPTAn emit blue-purple light in solution (Fig. 6b ande). Tn/Dn only have one large emission peak at 398/406-410 nm in solution, respectively, and in the thin film state, one emission broad peak at around 404-407/392-394 nm (Fig. 6c), respectively, due to the molecular conformational changes in the solid state. In solution, DTPTBn compounds have two isolated strong emission peaks at 418 nm (strongest) and 442 nm, and DTPTAn compounds have two strong emission peaks at 396 nm (strongest) and 417 nm. In thin films, DTPTBn and DTPTAn have only one, though broad, emission peak at about 460 nm and 450 nm, respectively (Fig. 6f). DTPTBn compounds emit at longer wavelengths of light than DTPTAn, likely because, in the thin-film state, the former compounds have more effective π-orbital overlap due to the planar nuclear core.

In summary, the optical properties are strongly affected by the molecular framework, whereas the peripheral alkyl chain length has little effect. The quantum yields (Φ) of these new compounds were measured in solution. In diluted THF solution, T12/D12 compounds have a Φ of 15.73/4.97%, respectively, while for their corresponding cyclized counterparts, DTPTB12/DTPTA12, these values are around 11.50/20.21%. It is understandable that, compared with its regio-isomer DTPTB12, DTPTA12 has a more twisted nuclear core which causes a lower degree of π-π aggregation in THF, and therefore the aggregation-caused-quenching (ACQ) of fluorescence is weaker and Φ is higher.

Since the molecular topology of these ditriphenylene DLCs effectively modulates the absorption and emission properties, we applied density functional theory at the B3LYP-D3/6-311++G(d,p) level to further understand the structure-property relationships of these new πconjugated organic systems, and study their optimized molecular conformations, frontier molecular orbital distributions, energy levels and band gaps. The corresponding methoxy derivatives of these π-conjugated molecular scaffolds were used as representatives in order to save the calculation time.

The HOMO/LUMO of D1/T1 (Fig. 7) showed wider energy gaps (4.41/3.99 eV, respectively) than their cyclized DTPTB1/DTPTA1 counterparts (3.65/3.87 eV, respectively) with the former HOMO (-5.04/-5.38 eV) and LUMO (-1.05/-0.97 eV) levels being relatively distinct from the latter HOMO (-4.95/-5.09 eV) and LUMO (-1.30/-1.22 eV) levels. These differences are logically explained by the larger extended π-conjugated systems and better molecular planarity through cyclization of DTPTB1/DTPTA1 compared to their precursors. In addition, these computational results were consistent with the measured photophysical properties: the fused π-systems DTPTB1/DTPTA1 showed red-shifted absorption and emission. Furthermore, D1/T1 and DTPTB1 displayed distinct HOMO/LUMO wave function distributions (see the ESI † for details), which implied the presence of intramolecular charge transfer (ICT), thus theoretically explaining their lowered fluorescence quantum yield (Φ). However, the HOMO and LUMO of DTPTA1 are located in the same parts of the molecular framework, in agreement with the highest Φ value of 20%. Furthermore, the core of DTPTAn deviating from planarity and the resulting low degree of aggregation in solution (see the following organogel part) might be another reason for this higher Φ value.

Organogels and morphology of xerogels

The presence of strong non-covalent bond interactions (π-π interactions, hydrogen bonds, dipole-dipole interactions, and hydrophilic/hydrophobic assembly, etc.) between organic molecules contributes to the formation of physical gels, [START_REF] Hirai | Enhanced Hole-Transporting Behavior of Discotic Liquid-Crystalline Physical Gels[END_REF] which have many potential applications. [START_REF] Monobe | Ambipolar Charge Carrier Transport Properties in the Homologous Series of 2,3,6,7,10,11-hexaalkoxytriphenylene[END_REF] We have recently reported thiophene-containing butterfly-shaped liquid crystals, i.e.DT, DTT, and BTBT (Chart 1) with an enlarged polycyclic aromatic nucleus that presented excellent solvent gelling properties (see some structurally related systems in Chart 1). [START_REF] Liu | Molecular design of benzothienobenzothiophene-cored columnar mesogens: facile synthesis, mesomorphism, and charge carrier mobility[END_REF][START_REF] Ma | Nonlinear Nonacenes with a Dithienothiophene Substructure: Multifunctional Compounds that Act as Columnar Mesogens, Luminophores, π Gelators, and p-Type Semiconductors[END_REF][START_REF] Ma | Butterfly-like Shape Liquid Crystals Based Fused-Thiophene as Unidimensional Ambipolar Organic Semiconductors with High Mobility[END_REF][START_REF] Hang | Butterfly Mesogens Based on Carbazole, Fluorene or Fluorenone: Mesomorphous, Gelling, Photophysical, and Photoconductive Properties[END_REF] As DTPTBn and DTPTAn also have an extended ditriphenylenothiophene rigid core, which is comparable to the DTT one, we anticipated that they would also behave as organic gelators.

In the experimental study, we found that both DTPTAn and DTPTBn compounds can easily form gels in organic solvents when the temperature was lowered or the concentration was increased. The critical gelation concentrations (CGCs) of DTPTAn were much higher than those of DTPTBn, indicating that the intermolecular π-π interactions of DTPTBn were stronger, in agreement with the higher planarity of the latter. DTPTB14 was selected as a representative example of this series to investigate gel properties in detail (Fig. 8). The gelling behavior of DTPTB14 was tested in a variety of organic solvents by heating the mixture to complete dissolution and then slowly cooling to room temperature. The critical gelation concentration (CGC) is usually used to describe the gelation capacity of π-gelators. DTPTB14 showed a very strong gelling capacity in both polar and non-polar solvents (Fig. 8). The gels also luminesce upon UV-light irradiation, as in films. On the other hand, DTPTAn also showed gelation capacity, but with CGC values higher than 20 mg mL -1 . Concentration-dependent 1 H NMR spectroscopy was chosen to explore the aggregation behavior of DTPTAn in solution. As shown in Fig. 9, it can be seen that the aromatic proton signals of DTPTA8 shift significantly to high fields with an increase in the concentration. Such a shift is associated with the increase of the intermolecular π-π interactions, which ultimately therefore will favor molecular aggregation. The difference in aggregation behavior between DTPTB and DTPTA essentially comes from their molecular structure. For DTPTB, these interactions already exist since the π-extended core is more planar and are very strong at low concentrations, thus favoring this behavior at an earlier stage, in contrast to the more distorted core structure of DTPTA, with the π-π and sulfursulfur interactions between the molecules being less efficient. To further analyze the gel behavior, xerogels from different organic solutions were prepared by the freeze-drying method, and their morphologies were characterized by scanning electron microscopy (SEM). As shown in Fig. 10, the gel morphology seems to be strongly related to the fixation of the solvent by the winding network structure with the formation of sheets (a/e), spheres (b), coral-like structures (c/d), and complex threedimensional network structures (f) (for DTPTB14, Fig.

Charge carrier mobility measured by the photocurrent time-of-flight (TOF) technique

POM and S/WAXS results displayed that polyaromatics DTPTBn and DTPTAn assembled both into columnar hexagonal mesophases. The π-π stacking of the ditriphenylenothiophene cores with eight alkyl mantles self-organize into one-dimensional supramolecular columns, which, as expected, can play the role of electron charge-carrier transport channels. On the other hand, the transient photocurrent time-of-flight (TOF) technique is a unique, accurate, direct, and simple method to measure the charge carrier mobility rate of organic semiconductors with a very long-range charge-hopping pathway. Furthermore, the charge carriers drift a distance of 15-20 μm along the π-π overlapping columns stacked by thousands of butterflyshaped molecules, which is very similar to the configuration in electronic devices for OLEDs and OPVs. The measured TOF mobility here was high compared with a standard hole transport OLED material triarylamine α-NPD with a mobility of 10 -4 cm 2 V -1 s -1 . 1b

The transient photocurrent decay curves were all in good shape and non-dispersive (Fig. 11a-d), demonstrating the high purity of these semiconductors and the excellent homeotropic alignment behavior (Fig. S6 and S7, ESI †) and thermal stability in ITO cells (Tables S6-S9, ESI †). However, only hole mobility was detected for both DTPTB12 and DTPTA12 (Fig. 11e andf), and no electron mobility signals could be captured. Therefore, the present TOF results showed that both compounds are purely p-type organic semiconductors. The hole mobility of DTPTB12 was relatively stable in the entire mesophase temperature range, with two regimes, a μhole ≈ 2.1 × 10 -3 cm 2 V -1 s -1 in the higher temperature Colhex mesophase that increases to ca. 3.0 × 10 -3 cm 2 V -1 s -1 in the lower temperature Col'hex mesophase during the cooling process, reflecting the formation of increasingly ordered 1D π-stacked nanostructures with the homeotropic configuration in the hexagonal phase. This TOF measurement is very sensitive because it is able to detect the phase transition between the two hexagonal phases, during the heating and cooling cycles, as shown by the jump of the hole mobility at exactly the same temperature recorded by DSC (Fig. 11e). This mobility value is about one order of magnitude higher than that of the α-NPD (3.6 × 10 -4 cm 2 V -1 s -1 , TOF) which is a standard OLED hole transport material. 1b This result indicates that DTPTBn compounds have promising applications as organic semiconducting materials. On the other hand, the hole mobility of its regio-isomer DTPTA12 was almost constant above 130 °C, and then decreased slightly following the temperature decrease. The hole mobility of DTPTA12, measured on cooling in the Colhex phase (μhole ≈ 6.4-2.7 × 10 -4 cm 2 V -1 S -1 ), was somehow about 10 times lower than that of the β-counterparts, but still in a reasonable range for the Colhex mesophase. According to the substitution pattern of the triphenylene fragments and DFT computational study, it was obvious that due to the flatter core of DTPTB than DTPTA, the intermolecular π-π stacks were consequently stronger in the former, which is obviously a more favorable situation for optimizing orbital overlaps and electron hopping. From the combination of S/WAXS data and the DFT-simulated molecular core structure, it was thus logical that the DTPTB compounds had higher μhole values than their DTPTA regio-isomer. However, despite all these, the substantial difference in the μhole value between both liquid crystalline regio-isomers, of about one order of magnitude, is still very intriguing. These results showed that regio-isomerism is an effective approach to control the core topology and the stacking ordering of these butterfly-shaped liquid crystals and that it has a significant impact on the semiconducting properties.

At this stage, it is delicate to a priori draw broad conclusions, as the comparison between different molecular systems may be affected by the experimental conditions (cell quality and thickness, alignment conditions, etc.) and other parameters such as the temperature of the experiment, the aliphatic volume fraction (length and number of alkoxy chains), and the symmetry of the mesophase (here, Colrecversus Colhex). However, at first sight, it can be seen that the hole mobility values measured for DTPTA12 and DTPTB12 compounds in the Colhex phase remain in a similar range (i.e. 10 -3 -10 -2 cm 2 V -1 s -1 ) to those of some structurally related butterfly-shaped liquid crystals measured in the same mesophase (Fig. S8, ESI †DT, BTBT, DTT, BDTO and CDTO for fused thiophene-containing compounds, and CTP, FTP and LTP for thiophene-free compounds). [START_REF] Liu | Molecular design of benzothienobenzothiophene-cored columnar mesogens: facile synthesis, mesomorphism, and charge carrier mobility[END_REF][START_REF] Ma | Nonlinear Nonacenes with a Dithienothiophene Substructure: Multifunctional Compounds that Act as Columnar Mesogens, Luminophores, π Gelators, and p-Type Semiconductors[END_REF][START_REF] Ma | Butterfly-like Shape Liquid Crystals Based Fused-Thiophene as Unidimensional Ambipolar Organic Semiconductors with High Mobility[END_REF][START_REF] Hang | Butterfly Mesogens Based on Carbazole, Fluorene or Fluorenone: Mesomorphous, Gelling, Photophysical, and Photoconductive Properties[END_REF] The hole mobility of DTPTB12 is amongst the highest within this set of compounds (with BDTO), and is even greater than that of the model triphenylene compound. 60 Moreover, the charge mobility does not seem to be correlated with the number of thiophene fragments fused, but instead with the degree of core distortion, which appears to have a deleterious effect (e.g., DTPTA). The non-fused thiophene system (Fig. S8, ESI †BPT) and the butterflies with no thiophene groups (Fig S8, ESI †CTP, FTP and LTP) self-organize in rectangular columnar (Colrec) phases at lower temperatures, and exhibit much higher μ values than in the Colhex, which can still be high in the Colhex phase (Fig. S8, ESI †FTP and LTP). Butterfly-shaped mesogens with slower nuclear motion in the columns, as LTP10 and LTP12, [START_REF] Hang | Butterfly Mesogens Based on Carbazole, Fluorene or Fluorenone: Mesomorphous, Gelling, Photophysical, and Photoconductive Properties[END_REF] both with dimethyl groups up and down the core plan for preventing free-rotation, display the highest mobility with the best electronic performance in the Colrec phase.

Conclusions

In summary, we have designed and synthesized regio-isomeric butterfly-shaped mesogens forming columnar liquid crystals by a simple, direct and efficient two-step reaction tandem. The effects of regio-isomerism on mesomorphous, photophysical and charge carrier mobility properties were investigated.

As far as the material properties are concerned, DTPTB compounds displayed broader Colhex mesophases with higher clearing temperatures, better gel properties with lower CGCs, better molecular planarity and higher hole mobility (ca. 3 × 10 -3 cm 2 V -1 s -1 ) than the isomeric compounds, emphasizing the strong effect of isomerism. These results all indicate that DTPTBn compounds have great potential for electronic applications as anisotropic organic gelators and organic semiconductors.

Although DTPTAn compounds are slightly inferior in the comprehensive performance of the material, they are easier to separate and purify, with higher synthetic yields. In addition, they produced blue-purple light in the film state and showed a higher fluorescence quantum yield in solution, which make DTPTAn more advantageous for optical applications.

The combined molecular design strategy and the Suzuki-Miyaura coupling/Scholl reaction tandem will be used in the synthesis of other polyaromatic regio-isomers. Further investigations of the original butterfly-shaped liquid crystalline π-conjugated systems are currently in progress.

Scheme 1

 1 Scheme 1 Molecular structures, nomenclature, yields and synthesis of the butterfly-shaped α,β-and β,β-fused ditriphenylenothiophene DTPTAn and DTPTBn regioisomers and precursors Dn and Tn (blue bonds, Suzuki-Miyaura cross-coupling; red bonds, Scholl oxidative cyclodehydrogenation).

Fig. 1

 1 Fig. 1 Representative POM photomicrographs: (a) T16 at 53 °C, (b) DTPTB16 at 200 °C, and (c) DTPTA8 at 155 °C.

Fig. 2

 2 Fig. 2 Phase transition temperature and thermotropic mesophase diagram of regioisomers DTPTBn and DTPTAn. Cr: crystalline phase; Col'hex, Colhex: hexagonal columnar mesophases (see the text); white arrows refer to heating or cooling (see also Table S4, ESI †).

Fig. 3

 3 Fig. 3 Representative S/WAXS patterns of the two regio-isomers DTPTB12 and DTPTA12 at various temperatures.

Fig. 4

 4 Fig. 4 Top-and side-views of DFT calculated optimized molecular structures of T1, D1, DTPTB1 and DTPTA1 (from top to bottom).

Fig. 5

 5 Fig. 5 Molecular structures and schematic representations of the supramolecular columns and organizations of both isomers into Colhex mesophases (hexagonal lattice in green). The molten aliphatic chains between the columns are not shown for clarity. Here molecules are presented in antiparallel stacking; ψ is the angle between hmol and hπ.

Fig. 6

 6 Fig. 6 Photophysical absorption and emission spectra of Tn, Dn, DTPTBn and DTPTAn: (a and d) UV-vis absorption in THF, c = 1 × 10 -5 mol L -1 ; (b and e) fluorescence emission in THF, c = 1 × 10 -5 mol L -1 ; (c and f) fluorescence emission in film. Excitation wavelengths: (b and c) Dn (λex = 280 nm) and Tn (λex = 310 nm); (e and f) DTPTAn (λex = 310 nm) and DTPTBn (λex = 310 nm). The signal at 212-214 nm in (a and d) is not an absorption band of the compounds but is due to the transparency limit of THF.

  Fig. 7 Frontier molecular orbitals (HOMO-LUMO) and energy levels of Tn, Dn, DTPTBn and DTPTAn.

Fig. 8

 8 Fig. 8 Top: Gelling properties of DTPTB14 in various organic solvents: (a/a′) hexane, (b/b′) cyclohexane, (c/c′) toluene, (d/d′) dichloromethane, (e/e′) tetrahydrofuran, and (f/f′) ethyl acetate. Top: 365 nm UV-light irradiation. Bottom: Sunlight exposure. G indicates the gel state; o and t denote the opaque and transparent gels, respectively; numbers in brackets correspond to the CGC in mg mL -1 .

Fig. 9

 9 Fig. 9 Concentration-dependent NMR spectrum of DTPTA8 in CDCl3.

10

 10

  of DTPTBn and DTPTAn, DTPTB14 and DTPTA12 were precipitated from a solution of dichloromethane by the addition of ethanol, and the morphology of the flocks was characterized by SEM. The self-assemblies produced by DTPTA12 and DTPTB14 were substantially different. DTPTA12 showed a pore granular morphology, while DTPTB14 presented continuous three-dimensional network structures, which likely results again from the distorted versus flat aromatic cores of DTPTAn and DTPTBn, respectively (Fig. S5, ESI †).

Fig. 10

 10 Fig. 10 SEM images of the xerogels of DTPTB14 in various organic solvents: (a) ethyl acetate, (b) hexane, (c) cyclohexane, (d) dichloromethane, (e) tetrahydrofuran, and (f) toluene.

  60

Fig. 11 (

 11 Fig. 11 (a-d) Transient photocurrent decay curves in the Colhex mesophases: (a) DTPTB12, 220 °C; (b) DTPTB12, 110 °C; (c) DTPTA12, 150 °C; and (d) DTPTA12, 100 °C. The insets show a loglog plot and the transit times are labeled. Cell thicknesses are 17.7 μm for DTPTB12 and 19.7 μm for DTPTA12, respectively. (e and f) Temperature dependence of charge carrier mobility by TOF: (e) DTPTB12 and (f) DTPTA12 ( : heating run, : cooling run; straight lines: transition temperatures recorded on heating, and dotted lines: transition temperatures recorded on cooling).

Table 1

 1 Temperature of the experiment (°C).b Molecular volume (Å 3 ) and density (g cm -3 ) calculated from partial volumes of reference substances: Vmol = Var + Vch, the sum of the volume of the aromatic part, Var (from reference compounds) and the volume of the chains, Vch = 8 × (nVCH2 + ΔVCH3), where 8 is the number of chains per molecule, n is the number of methylene groups per chain, VCH2 is the volume of one methylene unit and ΔVCH3 is the volume contribution of the end methylene (as a function of temperature in °C), see

			Geometrical		parameters	of		the		Colhex mesophases
	of DTPTBn and DTPTAn compounds
	Compound	T a	Vmol b	 b	a c	A c	hmol d	h () d	 e	core f	Dcyl g	sch h	q i
	s
	DTPTB12	95	3392	0.96	33.04	945.16	3.59	3.47 (26)	15	0.184	14.89	20.98	0.93
		120	3458	0.94	33.12	949.80	3.64	3.50 (11)	16	0.181	14.78	21.14	0.93
		210	3730	0.87	32.12	893.68	4.17	3.65 (-)	29	0.168	13.81	22.63	0.93
	DTPTB14	120	3921	0.92	34.12	1008.29	3.89	3.50 (9)	26	0.159	14.30	21.85	0.96
		180	4116	0.88	33.72	984.54	4.18	3.61 (-)	30	0.152	13.80	22.65	0.95
	DTPTB16	120	4385	0.91	36.63	1161.81	3.77	3.49 (11)	22	0.142	14.52	21.52	0.94
		180	4600	0.87	35.82	1111.10	4.14	3.61 (-)	29	0.136	13.86	22.54	0.95
	DTPTA8	95	2480	1.01	27.27	644.21	3.85	3.55 (20)	23	0.252	14.38	21.74	0.97
		150	2595	0.97	26.87	625.26	4.15	3.63 (14)	29	0.241	13.85	22.57	0.97
	DTPTA10	100	2947	0.98	29.39	747.90	3.94	3.57 (14)	25	0.212	14.21	21.99	0.98
		170	3122	0.92	28.52	704.47	4.43	3.78 (-)	31	0.200	13.40	23.32	0.99
	DTPTA12	80	3354	0.97	32.57	918.91	3.65	3.53 (-)	15	0.186	14.76	21.16	0.95
		150	3542	0.91	31.16	841.15	4.21	3.67 (-)	29	0.176	13.75	22.73	0.97
	a

ref. 56; ρ = MW/(NA•Vmol). c Lattice parameter, a (Å), and area, A = a 2 √3/2 (Å 2

Table 2

 2 Spectroscopic parameters of Dn and Tn and DTPTAn and DTPTBn in solution and thin film states a

			Dn and Tn compounds					DTPTAn and DTPTBn compounds
		λabs	ε	λem (sol)	QY a	λem (film)		λabs	ε	λem (sol)	QY a	λem (film)
	D8	242	6.31	410	5.62	392	DTPTA8	304	13.5	396	19.79	447
		292	3.24					352	4.71	417
		334	5.31					370	4.29
								384	3.36
	D10	242	6.39	406	5.66	392	DTPTA10	304	12.1	396	19.70	450
		292	3.21					352	4.19	417
		334	4.71					370	3.82
								384	3.01
	D12	242	7.34	407	4.97	394	DTPTA12	304	7.70	396	20.21	447
		292	3.44					352	2.70	417
		334	5.54					370	2.46
								384	1.94
	T12	282	4.90	398	15.73	404	DTPTB12	258	4.77	418	11.50	464
		326	2.67					298	8.19	442
								324	4.94
								378	3.08
	T14	280	6.87	398	15.91	407	DTPTB14	258	5.76	418	11.90	467
		326	3.96					298	9.20	442
								324	5.86
								378	3.62
	T16	282	5.42	398	15.51	404	DTPTB16	258	6.58	418	11.78	463
		326	3.02					298	1.13	442
								324	6.71
								378	4.27

Acknowledgements

This research was financially supported by the National Natural Science Foundation of China (NSFC, Fund numbers: 51273133 [KQZ], 51773140 [KQZ], and 51973143 [PH]). KQZ and HM are grateful to the support from the NSFC-JSPS joint project (50811140156). BD thanks CNRS and the University of Strasbourg for their support.

Footnote † Electronic supplementary information (ESI) available: Materials, experimental and synthetic procedures, TGA, POM, DSC, S/WAXS, SEM, TOF, DFT, NMR, and HRMS. See https://doi.org/10.1039/d2nj00655c


Samuel Jeanjean

Fabien Halter

Guillaume Legros

Christian Chauveau

Christian Chauveau Pyrometry

Pyrometry technique Radiation and temperature of aluminum flame

Workshop on MECRE, 31st October and 1st November 2022

Pyrometry technique

Radiation and temperature of aluminum flame S. JEANJEAN (1) , F. HALTER (1,2) , G. LEGROS (1,2) , C. CHAUVEAU (1) (1) ICARE-CNRS, UPR3021, 1C av. de la Recherche Scientifique , 45071 Orléans, France

(2) Université d'Orléans Cedex 2, France Background Objectives

(f) (g) (h) (i) (n) (m) (p) (q) (l) (k) (o) (e) (d) (c) (b) (a) (j) (r) Experimental Optical Setup: (a) Backlight (b-e-j) Lens (c)Pinhole (d) Chopper (f) Laser (g) Burner (h) Photodiode (i) Acquisition system (n) Black surface (m) (p) 905nm filter (l) 700nm filer (k-q) Cameras (o) Signal generator (r) Fluxmeter

Solid angle visualization of the fluxmeter

General context:

• The severity of the restriction on pollutant emissions pushes car manufacturers towards a sophistication of the power train, and even the total electrification of the vehicles, questioning the way of storing the onboard energy and the conversion mode of the primary energy.

ANR project:

Several research teams are studying metal combustion as an energetic vector for transportation:

• The flame is considered as axisymmetric and the scattering is neglected.

The experimental set-up provides four images ; two pairs of images at 905 nm and 705 nm with and without backlight.

Each pair of images is used to evaluate the absorption at each point.

Work in progress (cameras are used)

Then with an onion-peeling-like deconvolution, it is possible to find out the local emissions considering the absorption.

The temperature is calculated thanks to the ratio of two Planck's law.

The experimental set-up allows to measure the radiated power, the power density and to acquire pictures. A spectrometer is also installed but not presented in this poster Work in progress (fluxmeter are used)

The plume radiation is negligible compared to the radiation emitted by the flame.

By observing several powder densities, the radiative power seems to be constant at around 40% for an equivalence ratio between 0.8 and 1.5. This behavior can be explained by the fact that the unburnt particles react with the ambient air and create a double flame (a premixed flame and a diffusion flame).

Under the equivalence ratio of 0.8 the drop in power highlights the stability issues and the extinction of the flame.

Image of a flame through the 700nm filter

Future works

• Describe a non-pressurized and a pressurized confined flame

• Observe the flame front closely

For the moment, too much noise is observed. The use of 4 images instead of 2 heightens this noise. This leads to an under evaluation of the absorption, especially near the flame front.

Local Absorption at 905nm

Local emission at 905nm

•

  Description of the aluminum flame • Product of the magnesium flame • Reduction of the metal oxide thanks to the solar energy • Feasibility of integration into a Presence of a 500W-pilot flame to ignite and stabilize the flame Legros, G., Wang, Q., Bonnety, J., Kashif, M., Morin, C., Consalvi, J.-L., Liu, F., 2015. Simultaneous soot temperature and volume fraction measurements in axis-symmetric flames by a two-dimensional modulated absorption/emission technique. Combustion and Flame 162, 2705-2719. https://doi.org/10.1016/j.combustflame.2015.04.006