Ping Fu

Michael A Quintero

Claire Welton

Xiaotong Li

Bruno Cucco

Michael C De Siena

Jacky Even

George Volonakis

Mikaël Kepenekian

Runze Liu

Mikaël Kepenekian

Craig C Laing

Vladislav Klepov

Yukun Liu

Vinayak P Dravid

G N Manjunatha Reddy

Can Li

Mercouri G Kanatzidis

Short Aromatic Diammonium Ions Modulate Distortions in 2D Lead Bromide Perovskites for Tunable White-Light Emission

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Introduction

Organic-inorganic hybrid perovskites are promising candidates for optoelectronic devices, such as solar cells [START_REF] Fu | Integrating large-area perovskite solar module with thermoelectric generator for enhanced and stable power output[END_REF][START_REF] Yang | Iodide management in formamidinium-lead-halide-based perovskite layers for efficient solar cells[END_REF][START_REF] Correa-Baena | Promises and challenges of perovskite solar cells[END_REF][START_REF] Kojima | Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells[END_REF] and light-emitting diodes (LEDs), [START_REF] Stranks | Metal-halide perovskites for photovoltaic and light-emitting devices[END_REF][START_REF] Yuan | Perovskite energy funnels for efficient light-emitting diodes[END_REF] owing to their unique optical properties and high tunability. The prototypical organic-inorganic hybrid perovskites exhibit the general formula AMX3 (A= methylammonium (MA, CH3NH3 + ), formamidinium (FA, CH3(NH2)2 + ), or Cs + ; M = Sn 2+ or Pb 2+ ; X = Cl -, Br -, or I -). Inorganic ions form a framework with corner-sharing octahedral [MX6] 4-units, and the small A-site cations occupy cuboctahedral voids within the framework and counterbalance the charge of the [MX6] 4-extended anion. [START_REF] Stoumpos | Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties[END_REF] When larger spacer cations are incorporated, the structure tends to split along different crystallographic planes, typically (100), (110), and (111) planes. The resulting two-dimensional (2D) perovskites have different band structures compared to their 3D counterparts and exhibit larger structural distortions within their metal halide octahedra. [START_REF] Ahmad | Dion-Jacobson Phase 2D Layered Perovskites for Solar Cells with Ultrahigh Stability[END_REF][START_REF] Tsai | High-efficiency two-dimensional Ruddlesden-Popper perovskite solar cells[END_REF][START_REF] Li | The 2D Halide Perovskite Rulebook: How the Spacer Influences Everything from the Structure to Optoelectronic Device Efficiency[END_REF] Among them, Dion-Jacobson (DJ)-phase 2D perovskites, consisting of short diamine spacer cations between the perovskite halide slabs, represent a special class in which the slabs can come very close together and form non-bonding X•••X contacts. [START_REF] Mao | Hybrid Dion-Jacobson 2D Lead Iodide Perovskites[END_REF][START_REF] Ke | Compositional and Solvent Engineering in Dion-Jacobson 2D Perovskites Boosts Solar Cell Efficiency and Stability[END_REF] This gives rise to unique phenomena, such as enhancing the electronic coupling between perovskite layers across the organic spacer and enhancing the charge transport. [START_REF] Li | Light-activated interlayer contraction in two-dimensional perovskites for highefficiency solar cells[END_REF] Further slicing of 2D perovskites results in metal halide wires and the formation of individual octahedra, 1D and 0D structures. [START_REF] Qian | A theoretical study of hybrid lead iodide perovskite homologous semiconductors with 0D, 1D, 2D and 3D structures[END_REF] Since 2D lead bromide perovskites exhibit broadband white-light emission, [START_REF] Dohner | Self-Assembly of Broadband White-Light Emitters[END_REF] several other 2D perovskites [START_REF] Mao | White-Light Emission and Structural Distortion in New Corrugated Two-Dimensional Lead Bromide Perovskites[END_REF][START_REF] Thirumal | Morphology-Independent Stable White-Light Emission from Self-Assembled Two-Dimensional Perovskites Driven by Strong Exciton-Phonon Coupling to the Organic Framework[END_REF][START_REF] Guo | Structural Diversity in Layered Hybrid Perovskites, A(2)PbBr(4) or AA'PbBr4, Templated by Small Disc-Shaped Amines[END_REF] and even some lower-dimensional metal halide hybrids, such as 1D [START_REF] Mao | Structural Diversity in White-Light-Emitting Hybrid Lead Bromide Perovskites[END_REF][START_REF] Yuan | One-dimensional organic lead halide perovskites with efficient bluish white-light emission[END_REF][START_REF] Lin | Low-Dimensional Organometal Halide Perovskites[END_REF] and 0D perovskitoids [START_REF] Zhao | Intrinsic white-light emission from low-dimensional perovskites for white-light-emitting diodes with high-color-rendering index[END_REF][START_REF] Sun | 0D Perovskites: Unique Properties, Synthesis, and Their Applications[END_REF] have also demonstrated white-light emission at room temperature. Because different spacer cations can impose various structural distortions, it is essential to study their effects on the nature of light emission properties of these materials. Moreover, identifying novel spacer cations will help further elucidate the relationship between cation choice, structural distortions, and light emission. Compared to the flexible aliphatic alkylammonium cations, mainly used for broad white-light emission, [START_REF] Yantara | Designing Efficient Energy Funneling Kinetics in Ruddlesden-Popper Perovskites for High-Performance Light-Emitting Diodes[END_REF][START_REF] Shi | 5-Ammoniumvaleric acid stabilized mixed-dimensional perovskite submicron platelets with white light emission[END_REF][START_REF] Kennard | Growth-Controlled Broad Emission in Phase-Pure Two-Dimensional Hybrid Perovskite Films[END_REF] the rigid aromatic cations offer several unique attributes to 2D perovskites. These include greater delocalization of the positive charge on the aromatic ring, shorter interlayer spacing, more hydrogen bonding between cations and anions, higher dielectric constants, and lower exciton binding energies. [START_REF] Li | Two-Dimensional Dion-Jacobson Hybrid Lead Iodide Perovskites with Aromatic Diammonium Cations[END_REF][START_REF] Shi | Two-Dimensional Organic-Inorganic Perovskite Ferroelectric Semiconductors with Fluorinated Aromatic Spacers[END_REF] Therefore, incorporating rigid aromatic cations into perovskite structures can result in various distortions and expansion for different types of broad-emission activity.

In this study, we employed three rigid isomers, viz. aromatic para-phenylene diammonium (pPDA), meta-phenylene diammonium (mPDA), and ortho-phenylene diammonium (oPDA) di-cations to template 2D lead bromide perovskites. We observed a nontrivial influence of each isomer on the crystal structure and physical properties. The first two cations are stabilized within the 2D perovskite motif, whereas oPDA leads to new 1D structural arrangements. The detailed crystallographic structures of 2D (pPDA)PbBr4, 2D (mPDA)PbBr4, 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2, and 1D (oPDA)2Pb3Br10 perovskites reveal the precise cation-anion interactions in these emissive materials. In addition, the local structures and packing interactions at the organic-inorganic interfaces were analyzed using [START_REF] Fu | Integrating large-area perovskite solar module with thermoelectric generator for enhanced and stable power output[END_REF] H and 207 Pb solid-state NMR spectra.

All the compounds exhibit white-light emission, the wavelength and width of which are linked to the level of distortion in the inorganic framework. Density functional theory calculations suggest that (pPDA)PbBr4 and (mPDA)PbBr4 are direct-band-gap semiconductors, and they exhibit larger electronic band-gaps and effective masses than those of the corresponding Ruddlesden-Popper phases (BA)2PbBr4 (BA=butylammonium). Films of these materials were prepared successfully from N, N-dimethylformamide (DMF) solvent. The film stability test shows that the stronger hydrogen-bonding interactions in the (mPDA)PbBr4 contribute to better thermal and light stability.

Results and discussion

Single-Crystal Growth and Structures

The new compounds were synthesized in hydrobromic acid (HBr) and hypophosphorous acid (H3PO2) medium using a step-cooling method as previously reported. [START_REF] Gao | m-Phenylenediammonium as a New Spacer for Dion-Jacobson Two-Dimensional Perovskites[END_REF] By tuning the stoichiometric ratios of lead oxide and spacer cations according to the chemical formula of (xPDA)PbBr4, 2D (pPDA)PbBr4 and (mPDA)PbBr4 perovskite structures are obtained in a targeted manner. The detailed procedure for the single-crystal growth is described in the experimental section. It is worth noting that the pPDA cation behaves differently in bromide and iodide chemistry. Previous work demonstrates that in the case of iodide, the pPDA cation forms a hydrated 1D perovskite structure (pPDA)PbI4•2H2O. [START_REF] Lemmerer | Two packing motifs based upon chains of edge-sharing PbI6 octahedra[END_REF] In the present case of bromides, we have the first example of 2D pPDAPbBr4 perovskite structure (n=1) with this cation.

The oPDA cation also behaves differently in the bromide system, which does not provide any evidence for the presence of perovskite "2D (oPDA)PbBr4". The oPDA cations give the 1D The precise crystal structures are determined using single-crystal XRD, and they are shown in Figure 2ah. The selected crystallographic data and structural refinements are listed in Table 1. The compounds are refined in the centrosymmetric triclinic space group (P1 ̅ ) for 2D (pPDA)PbBr4 and in the monoclinic space group (C2/c) for 2D (mPDA)PbBr4. The octahedra in (pPDA)PbBr4 and (mPDA)PbBr4 form "corner-sharing" 2D perovskite structures. The adjacent inorganic layer with respect to the nearest metal-metal distance for the 2D (pPDA)PbBr4 and (mPDA)PbBr4 are slightly offset, with a layer shift factor of (0.15, 0.15) and (0.04, 0.04), respectively, and they formally belong to the Dion-Jacobson (DJ) family (n=1 members). [START_REF] Mao | Hybrid Dion-Jacobson 2D Lead Iodide Perovskites[END_REF][START_REF] Mao | Two-Dimensional Hybrid Halide Perovskites: Principles and Promises[END_REF][START_REF] Vasileiadou | Insight on the Stability of Thick Layers in 2D Ruddlesden-Popper and Dion-Jacobson Lead Iodide Perovskites[END_REF][START_REF] Marchenko | Layer Shift Factor in Layered Hybrid Perovskites: Univocal Quantitative Descriptor of Composition-Structure-Property Relationships[END_REF] The adjacent [PbBr4] 2-slabs are close but do not interact. For comparison, the standard van der Waals distance between the two bromine atoms is 3. In the ideal tetragonal structure of the n=1 members, the four nearest metal atoms in a plane form a square, and the octahedra are untitled (e.g., the Pb-Br-Pb angle is 180 °), but for the tilted structures, as in the present cases, two opposite edges of the square are "pulled-in" and the other two are "pushed-out." Specifically, the average Pb-Br-Pb angles were 142.08° and 143.03° for the 2D (pPDA)PbBr4 and (mPDA)PbBr4, respectively, revealing considerable octahedra tilting. For comparison, i) the typical RP phase (BA)2PbBr4 and (PEA)2PbBr4 (PEA: phenylethylamine), the average Pb-Br-Pb angles are 154.82 o and 151.46 o , respectively; [START_REF] Shibuya | Poly[bis(phenethyl-ammonium) [di-bromidoplumbate(II)]-di-mu-bromido[END_REF][START_REF] Smith | Structural origins of broadband emission from layered Pb-Br hybrid perovskites[END_REF] ii) the new hybrid layered A2PbBr4 (A = 1,2,4-triazolium or acetamidinium) and AA′PbBr4 (A = 1,2,4-triazolium and A′= imidazolium), templated by small disc-shaped amines, the average Pb-Br-Pb angles are 166.09 o , 164.4 o and 176.98 o , respectively. [START_REF] Guo | Structural Diversity in Layered Hybrid Perovskites, A(2)PbBr(4) or AA'PbBr4, Templated by Small Disc-Shaped Amines[END_REF] It is evident that the average Pb-Br-Pb angles of the 2D (pPDA)PbBr4 and (mPDA)PbBr4 are the smallest. Thus, the short aromatic diammonium ions can modulate much more distorted octahedra in 2D lead bromide perovskites than in the RP and hybrid layered cases. The selected bond lengths and angles in the [PbBr4] parts are listed in Table 2. The details of the structural distortion will be discussed later. Additionally, both cations have phenyl groups, aromatic ring stacking π-π interactions can occur if the distance between aromatic rings ranges from 3.3 to 3.8 Å. [START_REF] Janiak | A critical account on pi-pi stacking in metal complexes with aromatic nitrogen-containing ligands[END_REF] The distances between the stacked phenyl group for 2D (pPDA)PbBr4 and 2D (mPDA)PbBr4 are 3.81 Å and 3.63 Å, respectively. Both the cations in the 2D single-crystal structures have their benzene ring arranged in parallel (Figures 2c,d). The cations in (mPDA)PbBr4 present stronger π-π stacking interactions, while in (pPDA)PbBr4 relatively weaker π-π stacking interaction.

The oPDA cations template two kinds of "edge-sharing" 1D non-perovskite structures (both in the triclinic space group P1 ̅ ), based on lead bromide with or without H3PO2 (Figure 3a-h 1). As shown in Figures 3d and3h, one zigzag chain is connected by one edge-sharing octahedron and the other one is connected by two edge-sharing octahedra. These structures have rarely been found before and will be explained in detail below. The short aromatic spacer cations, mPDA and pPDA strongly influence the perovskite structure and properties. To understand the distortions in these structures, we calculated the mean distortion level in the octahedra of each compound. The bond length distortion, (Δd) is defined by ∆𝑑 = (

) ∑[

|𝑑 𝑛 -𝑑| 𝑑 ],
where d is the average Pb-Br bond distance and dn represent the six individual bond distances. [START_REF] Lufaso | Jahn-Teller distortions, cation ordering and octahedral tilting in perovskites[END_REF][START_REF] Alonso | Evolution of the Jahn-Teller distortion of MnO6 octahedra in RMnO3 perovskites (R = Pr[END_REF] The deformation of the octahedra can also be seen from the values of the bond angle variance (σ) calculated by the expression

σ 2 = ∑ 𝑖 12 1 (θi -90) 2 /11
, where θi is the individual Br-Pb-Br bond angle. [START_REF] Robinson | Quadriatic Elongation -Quantitative Measure of Distortion in Coordination Polyhedra[END_REF] The bond length distortion and bond angle variance for the compounds are listed in Table 2. For 2D structures, the degree of bond angle variance and bond length distortion, in descending order, are 2D (mPDA)PbBr4 > 2D (pPDA)PbBr4. Thus, the asymmetric arrangement of NH3 + groups (meta) in the aromatic diammonium ions exert larger octahedra tilting compared to the symmetric cases (para). The bond angle and bond length variance of 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2 is smaller than those of 2D compounds.

Cation-Anion Interactions

Hydrogen bonding plays an important role in stabilizing octahedral tilting and inducing structural distortion. [START_REF] Lee | Role of hydrogen-bonding and its interplay with octahedral tilting in CH3NH3PbI3[END_REF] Further insights into hydrogen-bonding interactions have been drawn from the single-crystal structures. For 2D (pPDA)PbBr4, the short distances of H••Br are ∼2.59, ∼2.72 and ∼2.88 Å, as shown in 4b). Thus, the stronger hydrogen-bonding interactions in (mPDA)PbBr4 might induce a larger distortion than that of (pPDA)PbBr4, which is in line with the analysis of crystal structure discussed above. In 1D

(oPDA)4(PbBr4)2Pb3Br10•4H3PO2 structure, the two sides of the ammonium cations can form hydrogenbonding interactions with the molecules H3PO2 as well as bromide anions (Figure 4c). Although the two sides of the ammonium cations can form hydrogen-bonding interactions with bromide anions, one H••Br bond is formed with one edge-sharing chain and the other one with two edge-sharing chains. The amino groups in the oPDA cations are tightly bound with these two kinds of chains, not with the same chain (Figure 4c). Thus, the amino groups of oPDA cations are too close to bridge with the same adjacent inorganic sheets simultaneously and unable to stabilize the 2D perovskite structures.

Short-Range Structures through Solid-State NMR Analysis

To further understand the organic layer and its impact on the organic-inorganic interfacial structure in these materials, we employed solid-state (ss) Nuclear Magnetic Resonance (NMR) spectroscopy. It has been used to gain insight into cation ordering and their dynamics, interfacial engineering, phase stability, and the degradation of products. [START_REF] Kubicki | NMR spectroscopy probes microstructure, dynamics and doping of metal halide perovskites[END_REF][START_REF] Spanopoulos | Tunable Broad Light Emission from 3D "Hollow" Bromide Perovskites through Defect Engineering[END_REF][START_REF] Kazemi | Molecular-Level Insight into Correlation between Surface Defects and Stability of Methylammonium Lead Halide Perovskite Under Controlled Humidity[END_REF][START_REF] Krishna | Nanoscale interfacial engineering enables highly stable and efficient perovskite photovoltaics[END_REF][START_REF] Dahlman | Dynamic Motion of Organic Spacer Cations in Ruddlesden-Popper Lead Iodide Perovskites Probed by Solid-State NMR Spectroscopy[END_REF] In this study, we used 1 H and 207 Pb magic-angle spinning (MAS) NMR spectroscopy to examine the local packing interactions of the three compounds. Particularly, 1 H and 207 Pb NMR chemical shifts are sensitive to intermolecular interactions at the organic-inorganic interface, and apical octahedral tilting. [START_REF] Piveteau | Solid-State NMR and NQR Spectroscopy of Lead-Halide Perovskite Materials[END_REF][START_REF] Raval | Understanding Instability in Formamidinium Lead Halide Perovskites: Kinetics of Transformative Reactions at Grain and Subgrain Boundaries br[END_REF] For para-, meta-, and ortho-diammonium cations (Figure 5a), the different local chemical environments of the proton sites are expected to lead to different frequencies. respectively. However, the (mPDA)PbBr4 phase exhibits peaks at 9.7 ppm (-NH3 + protons, green dots), 7.6 ppm (aromatic protons, blue dots) and a partially resolved peak at 6.8 ppm (purple dot) associated with the proton that is in the meta position with respect to -NH3 + groups. By analyzing and comparing the 207 Pb chemical shifts, we obtained insight into the organic-inorganic interfaces such as apical octahedral tilting and octahedral penetration. In the 207 Pb NMR spectra (Figure 5c), the pPDA and mPDA 2D phases displayed peaks at -50 and 50 ppm with a relative difference in the lead shift,  = 100 ppm, corroborating the different local chemical environments of PbBr 6 and octahedral tilting.

For these 2D perovskites, the 1 H chemical shift of -NH 3 + site at 9.7 ppm in the mPDA cation suggests stronger hydrogen-bonding interactions with lead bromide octahedra than the pPDA cations with the 1 H chemical shift of -NH3 + site at 9.2 ppm, which is in line with the analysis of crystal structure discussed above. In contrast, the 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2 displays a peak at 10 ppm associated with -NH3 + protons (green dots) that involve in hydrogen-bonding interactions with H3PO2. Further, a broad distribution of peaks in the 5.5-9.0 ppm range is due to aromatic protons (blue dots). As mentioned above, the -NH3 + groups in the oPDA cations cannot develop hydrogen-bonding interactions with the PbBr6 octahedra from adjacent layers of lead octahedra owing to steric effects, thus forming a 1D phase. Next, we applied 2D 1 H-1 H double-quantum single-quantum (DQ-SQ) correlation spectroscopy to probe packing interactions within the organic layer. In such experiments, 2D peaks are detected for through-space inter-and intramolecular dipolar-coupled 1 H-1 H pairs within a distance of 5 Å. These manifest as ondiagonal (chemically equivalent protons) and off-diagonal (chemically inequivalent proton sites) signals.

The DQ chemical shift evolves at the sum of the SQ chemical shifts, yielding to chemical shift dispersion in the vertical DQ axis twice as large as the horizontal SQ axis. The 2D 1 H-1 H DQ-SQ correlation spectra of the three systems (Figures 5d-5f) show different DQ peaks, which can be attributed to different packing interactions. For 2D (pPDA)PbBr4 (Figure 5d), the on-diagonal 1 H DQ peak at 16.2 ppm corresponds to the intramolecular dipolar interactions between the aromatic protons as depicted by the two blue dots. The off-diagonal DQ peak at 17.5 ppm corresponds to dipolar interactions between -NH 3 + and aromatic protons (green and blue, respectively). The on-diagonal peak at 18.8 ppm corresponds to the intramolecular dipolar interaction within the -NH 3 + groups, as represented by the two green dots. The intermolecular contributions to this peak are negligible because the nearest distance between the intermolecular -NH3 + groups in pPDA cations is 5 Å. In 2D (pPDA)PbBr4, the intermolecular aromatic H-H proximities are also > 4 Å. For comparison, the 1 H DQ spectrum of 2D (mPDA)PbBr4 (Figure 5e) exhibits an off-diagonal DQ peak at 14.4 ppm due to the through-space inter-and intramolecular dipolar interactions between the aromatic protons as depicted in blue and purple dots, and the off-diagonal DQ peak at 17.3 ppm is due to the intramolecular through-space proximity between the -NH3 + (green dots) and aromatic protons (blue dots), respectively. The strong intensity on-diagonal 1 H DQ peak at 19.4 ppm is due to the intramolecular dipolar interactions in -NH3 + groups, and the weak intensity on-diagonal 1 H DQ peak at 15.2 ppm is attributable to both inter and intramolecular 1 H-1 H proximities between aromatic protons that are in meta position with respect to each other (blue dots) for which the interatomic distance is ~4 Å.

For the 1D (oPDA)4(PbBr4)2Pb3Br10•4PO2 system (Figure 5f), we observed a broad distribution of the DQ peak at ~15 ppm, corresponding to intra-and intermolecular interactions between the aromatic protons depicted by the two blue dots. The broad signals are due to the substantial self-assembly by oPDA cations, which lead to one-to-one as well as slip-stacked dimers, resulting in different - stacking and C-H- interactions. For example, the hydrogen atoms depicted in the blue and red dots exhibit different aromatic ring current effects, leading to a broad distribution of peaks in the 6-9 ppm range. A weak off-diagonal DQ peak further corroborates this at 17.6 ppm that originates from intermolecular dipolar interactions between the aromatic (blue dots) and -NH3 + protons (green dots) for which the intermolecular 1 H-1 H distance is ~3.1 Å. In addition, the distinct on-diagonal DQ peaks at 20.2 ppm are ascribed to the intramolecular dipolar interactions between the adjacent -NH3 + protons depicted by the two green dots.

These structural differences contribute to different optical and electronic properties, as discussed below.

Optical Properties, White-Light Emission and Work Functions

The optical absorption spectra of the three compounds are shown in Although the optical spectra show sharp absorption edges, the photoluminescence (PL) spectra of all the compounds exhibit broadband emission features, as shown in Figure 6b. For 2D (mPDA)PbBr4, the maximum of PL peak is centered at 2.08 eV and the PL emission exhibits the broadest peak from 2.47 eV (502 nm) to 1.74 eV (713 nm) (Full Width Half Maximum (FWHM):0.73 eV (211 nm)) due to the largest octahedra distortion. For 2D (pPDA)PbBr4, the maximum of PL peak is centered at 2.35 eV and the PL peak exhibits the second broader peak with an FWHM of 0.69 eV (158 nm) (from 2.70 eV (459 nm) to 2.01 eV (617 nm)). It has been argued that the broad photoluminescence (PL) emission is associated with a high level of bond length distortion of the structure. [START_REF] Mao | White-Light Emission and Structural Distortion in New Corrugated Two-Dimensional Lead Bromide Perovskites[END_REF][START_REF] Wang | Perovskite light-emitting diodes based on solution-processed selforganized multiple quantum wells[END_REF] It is noteworthy to draw comparison to the published structure of the lead iodide analogues. The 2D (pPDA)PbI4 cannot be stabilized with pPDA cation, but the synthesis and photo-physical characterization of 2D (mPDA)PbI4 were previously reported in our group. [START_REF] Gao | m-Phenylenediammonium as a New Spacer for Dion-Jacobson Two-Dimensional Perovskites[END_REF] Although the average Pb-I-Pb angle for 2D (mPDA)PbI4 is 143.8 o , similar to that in (mPDA)PbBr4 (Table 2), the bond length distortion of the octahedron in 2D (mPDA)PbI4 is smaller than in (mPDA)PbBr4. This could be linked to the narrower PL emission of 2D (mPDA)PbI4 than that of (mPDA)PbBr4.

The 1D (oPDA) 4 (PbBr 4 ) 2 Pb 3 Br 6c), we observe that the average lifetimes for 2D (pPDA)PbBr4, 2D (mPDA)PbBr4, and 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2 are 3.05 ns, 3.17 ns, and 1.72 ns, respectively (Table 3), which is an indication of slower carrier recombination and improved carrier transport for 2D compounds compared to the 1D system. [START_REF] Dhanabalan | Simple fabrication of layered halide perovskite platelets and enhanced photoluminescence from mechanically exfoliated flakes[END_REF] The measured average lifetime of each sample was fitted using a three-exponent function (details are provided in the experimental section). To further explore the mechanism of the broadband emission, we performed variable-temperature PL from 80 K to 290 K for 2D (mPDA)PbBr4 and (pPDA)PbBr4 compounds (Figure S4).

Both the PL spectra present a significant red shift, decreased PL intensity and broadening of the PL peak with increasing temperature. Thus, trap-mediated excitonic recombination or self-trapped excitons (STEs) might also contribute to the broadband emission. [START_REF] Smith | Tuning the Luminescence of Layered Halide Perovskites[END_REF][START_REF] Cortecchia | White light emission in low-dimensional perovskites[END_REF][START_REF] Febriansyah | Metal Coordination Sphere Deformation Induced Highly Stokes-Shifted, Ultra Broadband Emission in 2D Hybrid Lead-Bromide Perovskites and Investigation of Its Origin[END_REF] 2. [START_REF] Ma | Tunable Color Temperatures and Emission Enhancement in 1D Halide Perovskites under High Pressure[END_REF] The photos of light emissive samples are captured under UV illumination (TOC). The CCT below 4500 K can produce neutral to warmwhite light. The (mPDA)PbBr4 has a CIE coordinate of (0.44, 0.46), which has a reddish-white emission compared to the white point at (0.33, 0.33). The CIE of (pPDA)PbBr4 and 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2 are (0.34, 0.44) and (0.21, 0.29), respectively, and they give CCT of 5450 K and >10000 K, respectively. Thus, they emit cold-white light. Considering these newly synthesized perovskite compounds could be used in future devices, it is important to know the energy positions of their valence and conduction bands in terms of the correct interface and device assembly. The valence band maximum (VBM) of the different compounds was measured by photoemission yield spectroscopy in air (PYS) (Figure 8a-d). Here we should mention that the conduction band minimum (CBM) is calculated from the difference between the VBM and the band-gap.

There might be an underestimation on the order of a few hundreds of meV due to the existence of exciton binding energy in the 2D perovskite material. [START_REF] Smith | Tuning the Luminescence of Layered Halide Perovskites[END_REF] We also compare the VBM and CBM of the three compounds with those of PbBr 2 and 3D MAPbBr 3 perovskite. [START_REF] Mao | Structural Diversity in White-Light-Emitting Hybrid Lead Bromide Perovskites[END_REF] The three compounds have a strong energy variation in the CBM (2.57 eV for (pPDA)PbBr4, 2.51 eV for (pPDA)PbBr4, and 2.04 eV for 1D

(oPDA)4(PbBr4)2Pb3Br10•4H3PO2 ), whereas the VBMs (5.49 eV for (pPDA)PbBr4, 5.54 eV for (pPDA)PbBr4, and 5.52 eV for 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2) remain almost constant. Compared with those of PbBr2 and 3D MAPbBr3, the VBM for the three compounds are similar to that of 3D MAPbBr3, while the VBM for the three compounds are between those of PbBr 2 and 3D MAPbBr 3. Thus, the different cations significantly influence the VBM and CBM, which is an important factor for the correct interface assembly.

Electronic Band Structure Calculations

The electronic band structures of (pPDA)PbBr4 and (mPDA)PbBr4 are shown in (Figure 9a-c), do not contribute to the band edges; However, for the 2D compounds, a few organic electronic states are found above the CBM, in contrast to the reference 2D compound (BA)2PbBr4. [START_REF] Smith | Structural origins of broadband emission from layered Pb-Br hybrid perovskites[END_REF] The out-of-plane interactions between halogens of adjacent inorganic slabs of 2D perovskite materials are known to play a crucial role in the electronic band structure, especially in iodides. [START_REF] Mao | Seven-Layered 2D Hybrid Lead Iodide Perovskites[END_REF][START_REF] Mao | Organic Cation Alloying on Intralayer A and Interlayer A ' sites in 2D Hybrid Dion-Jacobson Lead Bromide Perovskites (A ')(A)Pb2B7[END_REF] To quantify this effect, we calculated the VBM and CBM band dispersion along the stacking direction for the 2D materials, as shown in green in Figure 9. For the VBM of (pPDA)PbBr4 and (mPDA)PbBr4, we found small dispersions of 110 meV and 83 meV, respectively, while for the CBM 18 meV and 21 meV, within the DFT-PBE0. This is not the case for (BA)2PbBr4, for which the dispersion is 0 because the apical interlayer bromines are too far away to interact. Finally, to explore the intralayer charge carrier transport of the 2D materials, we calculated their in-plane effective masses for holes and electrons and compared them to those of (BA)2PbBr4. The effective masses of (pPDA)PbBr4 and (mPDA)PbBr4 are found slightly larger, me = 0.36 and 0.34 and mh = 0.53 and 0.50 m0, than those for (BA)2PbBr4, me = 0.19 and mh = 0.33 m0. This observation is consistent with the larger inplane distortions of the Pb-Br octahedra.

Our results show that the here-observed distortions of layered halide perovskites tend to increase the bandgap and the in-plane hole and electron effective masses. Yet, we find no direct relation between the electronic band structure of the compoudns and their emission. Hence, the existence of low-energy whitelight emission, and its observed correlation with structural distortions are not originating from the electronic structures of (pPDA)PbBr4 and (mPDA)PbBr4. Other possible physical mechanisms underly the observed emission, and can be further explored, such as exciton trapping facilitated by the strong distortions in the inorganic parts of the structures, as hinted by the results of the temperature-dependent PL spectra of (pPDA)PbBr4 and (mPDA)PbBr4 (Figure S4).

Film Properties and Stability

Most perovskite films reported previously were made from mixtures of the precursor components. [START_REF] Hadi | Improving the Stability and Monodispersity of Layered Cesium Lead Iodide Perovskite Thin Films by Tuning Crystallization Dynamics[END_REF] Herein, we dissolve the single crystals directly in the solvent, and the memory seeds could enable high structural phase purity in the 2D perovskite film. [START_REF] Sidhik | Memory Seeds Enable High Structural Phase Purity in 2D Perovskite Films for High-Efficiency Devices[END_REF] Notably, the (pPDA)PbBr4 compounds form a clear N,N-DMF solution, but a dark blue solution forms in dimethyl sulfoxide (DMSO). The 2D (pPDA)PbBr4 cannot dissolve in acetonitrile (ACN) and gamma-butyrolactone (GBL) (Figure S7). Thus, all three crystals are dissolved in anhydrous DMF. The details of the film assembly are described in the experimental section.

The XRD patterns of the films (Figure 10a) exhibit low-angle basal Bragg peaks below 2θ = 10°, similar to the powder XRD pattern of single-crystal materials. The optical absorption spectra (Figure 10b) confirm the formation of 2D perovskite pure phases for (pPDA)PbBr4 and (mPDA)PbBr4 films. For 1D (oPDA)4PbBr4Pb3Br5•4H3PO2, the absorption edge is 3.45 eV, which is also similar to the material itself. The PL from the 2D (pPDA)PbBr4 and (mPDA)PbBr4 films still show broad emission (Figure 10c). In addition, all the average lifetimes are comparable to the bulk materials at 1.93 ns, 3.17 ns, and 1.88 ns for 2D

(pPDA)PbBr4, 2D (mPDA)PbBr4, and 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2 films, respectively (Figure 10d and Table 3).

We also investigated the stability of the three-hybrid lead bromide perovskite films to assess their potential in devices (Figure S8). We used a continuous UV irradiation illumination test in the air (temperature, 22 °C; humidity, 35%). All the color and XRD results for the three films remain constant for more than 24 h. The long-term thermal stability test was conducted on a hot plate at 80 °C in the air (temperature 22 °C, humidity 35%). According to the XRD results, only the (mPDA)PbBr4 films remain stable during continuous heating in air for more than 24 h. We find splitting in the low-angle (2θ < 10°) Bragg peaks for the other two cases, suggesting the structural decomposition. The color for the (pPDA)PbBr4 films changes from white to dark grey, and light pink for the 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2 films, after 24 h heating in air. Thus, the (mPDA)PbBr4 films exhibit the best thermal stability due to the stronger hydrogenbonding interactions in its structure.

Conclusions

The influence of ammonium group positions in the short rigid aromatic moiety of phenylene diammonium family on the crystal structures of low-dimensional lead bromides is strong and leads to 2D for 5-10 min at ∼200 °C until the solution became clear. Then 64.9 mg (0.6 mmol) of pPDA was added directly to the above solution under the same conditions until complete dissolution.

Finally, the solution was cooled to 120 °C and eventually to room temperature to obtain white plate-like crystals of pPDAPbBr4. The product was isolated by suction filtration followed by drying in a filtration funnel for 30 min. The yield obtained was 750 mg (58.9% of total Pb content).

4.1.2. For (mPDA)PbBr4 n = 1. 446.4 mg (2 mmol) of PbO powder was dissolved in 3 mL of hydrobromic acid and 1 mL of H3PO2 solution (or without 1 mL of H3PO2) by heating with constant stirring for 5-10 min at ∼200 °C until the solution became clear. Then 64.9 mg (0.6 mmol) of mPDA was added directly to the above solution under the same conditions until complete dissolution. Finally, the solution was cooled to 120 °C and eventually to room temperature to obtain white plate-like crystals of mPDAPbBr4. The product was isolated by suction filtration followed by drying in a filtration funnel for 30 min. Yield obtained was 366 mg (28.7% of the total Pb content).

4.1.3. For (oPDA)4(PbBr4)2Pb3Br10•4H3PO2. 446.4 mg (2 mmol) of PbO powder was dissolved in 3 mL of hydrobromic acid and 1 mL of H3PO2 solution by heating with constant stirring for 5-10 min at ∼200 °C until the solution became clear. The only difference for 1D (oPDA)4Pb3Br10 was the absence of 1 mL of H3PO2. Next, 64.9 mg (0.6 mmol) of oPDA was added directly to the above solution with the same conditions until complete dissolution. Finally, the solution was cooled to 120 °C, and crystals were obtained at room temperature. The product was isolated by suction filtration followed by drying in a filtration funnel for 30 min. Yield obtained was 186 mg (14.6% of total Pb content).

Film Fabrication.

FTO glass substrates were first cleaned by sequential sonication in acetone and isopropanol for 15 min each. Subsequently, the FTO substrates were dried with nitrogen and treated for 30 min using ultraviolet ozone (UVO). Solutions of the studied materials were prepared by dissolving 100 mg of dried crystals in 200 μL of anhydrous DMF solvent. The substrates were heated at 110 °C on a hot plate for 10 under N2 atmosphere. Then, the precursor solution was spin-coated at 5000 rpm for 30 s in a glovebox under a N2 atmosphere. Unless otherwise specified, all the samples were spun at a MAS frequency of 50 kHz. [START_REF] Fu | Integrating large-area perovskite solar module with thermoelectric generator for enhanced and stable power output[END_REF] H relaxation delays were determined from the saturation recovery measurements and analyses. Single-pulse 1 H MAS NMR spectra were acquired by co-addition of 32 transients. The 1D 207 Pb MAS experiments were carried out using a spin-echo pulse sequence. Each spectrum was acquired with 4096 coadded transients using a relaxation delay of 800 ms. For all compounds, 2D 1 H-1 H double-quantum (DQ)-single-quantum (SQ) NMR spectra were acquired using a back-to-back sequence under fast MAS. 64 A rotor-synchronized t1 increment of 20 s was applied with a DQ excitation time of 40 µs corresponding to two rotor periods (2r). The 1 H DQ dimensions were acquired using 128 t1 FIDs, each with 16 co-added transients. The 1 H experimental spectra were calibrated with respect to that

Single-Crystal X-ray

(oPDA) 4 (

 4 PbBr4)2Pb3Br10•4H3PO2 halide when H3PO2 is added to the reaction, and the 1D (oPDA)2Pb3Br10 structure when the reaction is carried out without H3PO2. The morphology and color of 2D (pPDA)PbBr4, 2D (mPDA)PbBr4, 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2, and 1D (oPDA)2Pb3Br10 are shown in Figure 1a-d. The successful synthesis of the desired materials in their pure form is further confirmed by powder X-ray diffraction (XRD) analysis, as shown in Figure S1. The observed patterns match the calculated values well.

Figure 1 |

 1 Figure 1 | SEM images for the (a) (pPDA)PbBr4, (b) (mPDA)PbBr4, (c) (oPDA)4(PbBr4)2Pb3Br10•4 H3PO2, (d) (oPDA)2Pb3Br10, respectively. Scale bar is 100 m.

  7 Å. Specifically, the closest interlayer Br•••Br distances are nonbonding at 4.43 Å and 4.60 Å for 2D (pPDA)PbBr4 and 2D (mPDA)PbBr4, respectively.

Figure 2 |

 2 Figure 2 | Different views of the 2D structures (a, c, e, g) (pPDA)PbBr4 and (b, d, f, h) (mPDA)PbBr4, respectively. The offset of the adjacent inorganic layer is estimated by the shift distance of Pb/2×length (Pb-Br).

  where d is the average Pb-Br bond distance and dn represent the six individual bond distances in the PbBr6 octahedron.

  ). Notably, the 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2 single crystal with H3PO2 has a large cell volume of 1763.1(7) Å 3 because of the inclusion of H3PO2 molecules, while a smaller volume of 776.2(3) Å 3 (1763.1/2=881.5 Å 3 normalized) is observed for 1D (oPDA)2Pb3Br10 without H3PO2 molecules. The two 1D structures exhibit different unit cells, but both have two different types of zigzag 1D chains in their unit cell (Table

Figure 3 |

 3 Figure 3 | Different views of the 1D structures (a, b, c) (oPDA)4(PbBr4)2Pb3Br104H3PO2 and (e, f, g) (oPDA)2Pb3Br10, respectively. Magnified images of one edge-sharing chain and two edge-sharing chains for (oPDA)4(PbBr4)2Pb3Br104H3PO2 (d) and (oPDA)2Pb3Br10 (h), respectively.

Figure 4a .

 4a Figure 4a. Similarly, the distances of H••Br (∼2.49 and ∼2.55 Å) for 2D (mPDA)PbBr4 are considerably shorter than those of 2D (pPDA)PbBr4 (Figure4b). Thus, the stronger hydrogen-bonding interactions in

Figure 4 |

 4 Figure 4 | H-Br interactions for the (a) (pPDA)PbBr4, (b) (mPDA)PbBr4, (c) (oPDA)4(PbBr4)2Pb3Br10•4 H3PO2.

  Figure 5bcompares the 1D 1 H NMR spectra of 2D (pPDA)PbBr4, 2D (mPDA)PbBr4, and 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2, where the different displacements of 1 H chemical shifts of the -NH3 + groups indicate different hydrogen-bonding interactions with the PbBr6 octahedra. For (pPDA)PbBr4, the partially resolved peaks at 9.2 and 8.1 ppm correspond to the -NH3 + (green dots) and aromatic protons (blue dots),

Figure 5 |

 5 Figure 5 | (a) Structure of p, m and oPDA spacer cations (b) solid-state 1D 1 H MAS NMR spectra of (pPDA)PbBr4, (mPDA)PbBr4, (oPDA)4(PbBr4)2Pb3Br104H3PO2, and (c) 1D 207 Pb MAS NMR spectra of (pPDA)PbBr4 and (mPDA)PbBr4 perovskites. Solid-state 2D 1 H-1 H DQ-SQ correlation NMR spectra of (d) (pPDA)PbBr4 (e) (mPDA)PbBr4 and (f) (oPDA)4(PbBr4)2Pb3Br104H3PO2, respectively. Spectral analysis is indicated by the color dots as indicated in the structures shown in (a). All spectra were acquired at 18.8 T ( 1 H = 800.1 MHz, 207 Pb = 167.4 MHz), with 50 kHz MAS at room temperature.

Figure 6a . 49 Figure 6 |

 6a496 Figure 6 | (a) Optical absorption spectra, (b) steady-state PL spectra, and (c) time-resolved PL spectra for 2D (pPDA)PbBr4, 2D (mPDA)PbBr4, 1D (oPDA)4(PbBr4)2Pb3Br10•4 H3PO2, respectively.

Figure 7 |

 7 Figure 7 | CIE color coordinates of (pPDA)PbBr4, (mPDA)PbBr4, (oPDA)4(PbBr4)2Pb3Br10•4H3PO2, in 1931 color space chromaticity diagram. The chromaticity coordinates (x, y), CCT, and CRI are calculated using the Color Calculator software (OSRAM Sylvania, Inc).

Figure 8 |

 8 Figure 8 | (a) Experimental energy band alignment (VBM and CBM) of lead bromide compounds of (pPDA)PbBr 4 , (mPDA)PbBr4, and (oPDA)4(PbBr4)2Pb3Br10•4H3PO2 compared with that of the 3D MAPbBr3 and PbBr2. Work function measurement for (b) 2D (pPDA)PbBr4, (c) 2D (mPDA)PbBr4, (d) 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2, respectively.

  Figure 9a-b. Both 2D materials are direct-band-gap semiconductors at the Γ point of the Brillouin zone. Employing the hybrid functional PBE0, which is known to correct the DFT underestimated band-gap values, 55,56 we calculated the electronic band-gaps of 3.40 eV for (pPDA)PbBr4 and (mPDA)PbBr4, slightly larger than the 3.11 eV electronic band-gap of the prototypical Ruddlesden-Popper layered perovskite (BA)2PbBr4. For 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2, the band-gap is indirect (Figure S5), and larger (4.11 eV within PBE0) than the 2D materials, in agreement with the experiments. The difference between the calculated band-gaps matches the trend observed in the optical absorption spectra (vide infra). As expected, the Pb s-orbitals and Br p-orbitals contribute to the VBM, while the conduction band minimum (CBM) is composed of mainly Pb p-orbitals (Figure S6). The organic spacer layers, whose states are shown by flat non-dispersive bands

Figure 9 |

 9 Figure 9 | Electronic structure for the 2D compounds (a) (pPDA)PbBr4, (b) (mPDA)PbBr4, and prototypical layered perovskite (c) (BA)2PbBr4. The band-gap is calculated employing the hybrid exchange-correlation functional PBE0. The direction that corresponds to the layer stacking is highlighted in green.

Figure 10 |

 10 Figure 10 | (a) PXRD patterns, (b) Optical absorption spectra, (c) steady-state PL spectra, and (d) time-resolved PL spectra for 2D (pPDA)PbBr4, 2D (mPDA)PbBr4, 1D (oPDA)4(PbBr4)2Pb3Br10•4 H3PO2 films, respectively.

1 .

 1 perovskite and 1D non-perovskite motifs all with broad white-light emission. When the amino groups are in the meta and para positions, the aromatic diammonium cations allow the formation of 2D network perovskite structures (n=1). When in the ortho positions, the cations stabilize only 1D structures. New insights into the local packing arrangements of organic spacers and organic-inorganic interfaces are obtained using high-field 1 H and 207 Pb solid-state 2D-NMR spectroscopy. The (pPDA)PbBr4 and (mPDA)PbBr4 perovskite exhibit different ammonium group penetrations and hydrogen-bonding interactions, which modulate the Br-Pb-Br bond angles and the tilting of the corner-sharing PbBr6 octahedra. The NMR shows large difference in the 207 Pb ( ~100 ppm) and 1 H chemical shifts of the -NH3 + groups ( ~0.5 ppm), among the compounds reflecting the local PbBr6 distortions. We also find structure-PL correlations, which link the level of the bond length distortions in the inorganic [PbBr4] 2-layer to the broad bandwidth of the PL emission. The bond length distortions for the three compounds in descending order are 2D (mPDA)PbBr4 > 2D (pPDA)PbBr4 >1D (oPDA)4PbBr4Pb3Br5•4H3PO2. Consequently, 2D (mPDA)PbBr4 compounds exhibit the broadest white light emission, while the narrowest white emission is observed for 1D (oPDA)4PbBr4Pb3Br5•4H3PO2. Density functional theory calculations for 2D (mPDA)PbBr4 and 2D (pPDA)PbBr4 suggests direct band-gaps with relatively broad valence and conduction bands along the in-plane directions, but a slightly indirect band-gap for the 1D (oPDA)4PbBr4Pb3Br5•4H3PO2. The (mPDA)PbBr4 film exhibits better thermal stability in ambient air than the other two films, presumably because of the stronger hydrogen-bonding interactions in the material. Therefore, our findings support the general belief that tuning the structural distortion in low-dimensional perovskites based on the shape and size of the spacer cation is an effective handle for designing single-source white-light emitters. For (pPDA)PbBr4 n = 1. 446.4 mg (2 mmol) of PbO powder was dissolved in 5 mL of hydrobromic acid and 1 mL of H3PO2 solution (or without 1 mL of H3PO2) by heating, with constant stirring

4 . 4 .

 44 Crystallography: Single-crystal XRD experiments were performed using a STOE IPDS II or IPDS 2T diffractometer with Mo Kα radiation (λ = 0.71073 Å) operating at 50 kV and 40 mA. Integration and numerical absorption corrections were performed using X-AREA, X-RED, and XSHAPE programs. The structures were solved by charge flipping and refined using the full-matrix least-squares in Olex2. The PLATON software was used to identify the twinning domains and validate the space groups of the compounds. Solid-state NMR spectroscopy. All solid-state magic-angle spinning (MAS) NMR experiments were carried out using an 18.8 T ( 1 H, 800.1 MHz) Bruker Avance Neo NMR spectrometer equipped with a 1.3-mm H-X probe head. Single-crystal samples of the 1D and 2D perovskites and precursor salts were separately packed into 1.3 mm zirconia rotors (outer diameter) fitted with VESPEL ® caps.

Table 1 |

 1 Crystal

	and Refinement Data for 2D (pPDA)PbBr4, 2D (mPDA)PbBr4, 1D (oPDA)4(PbBr4)2Pb3Br10•4 H3PO2
	and 1D (oPDA)2Pb3Br10 at 293 K, respectively.
	Empirical formula	(pPDA)PbBr4	(mPDA)PbBr4	(oPDA)4(PbBr4)2 Pb3Br10•4H3PO2	(oPDA)2Pb3Br10
	Formula weight	636.99	636.99	3237.2	1640.99
	Crystal system	triclinic	monoclinic	triclinic	triclinic
	Space group	P1 ̅	C2/c	P1 ̅	P1 ̅
		a = 7.4473(15) Å,	a = 21.776(4) Å,	a = 7.7604(16) Å,	a = 7.5730(15) Å,
		α = 70.53(3)°	α = 90°	α = 89.87(3)°	α = 104.45(3)°
	Unit cell dimensions	b = 8.7255(17) Å, β = 78.47(3)°	b = 8.8113(18) Å, β = 107.16(3)°	b = 14.578(3) Å, β = 77.79(3)°	b = 10.323(2) Å, β = 96.43(3)°
		c = 11.036(2) Å,	c = 7.3950(15) Å,	c = 16.021(3) Å,	c = 11.235(2) Å,
		γ = 89.40(3)°	γ = 90°	γ = 84.54(3)°	γ = 110.67(3)°
	Volume	661.2(3) Å 3	1355.7(5) Å 3	1763.1(7) Å 3	776.2(3) Å 3
	Z	2	4	1	1
	Density (calculated)	3.199 g/cm 3	3.121 g/cm 3	2.983 g/cm 3	3.511 g/cm 3
		-9<=h<=9,	-28<=h<=27,	-9<=h<=7,	-9<=h<=12,
	Index ranges	-11<=k<=10,	-11<=k<=11,	-17<=k<=17,	-16<=k<=16,
		-14<=l<=14	-9<=l<=9	-19<=l<=19	-17<=l<=18
	Reflections collected	10586	5664	14009	12512
	Independent reflections	3027 [Rint = 0.0864]	1556[Rint = 0.1141]	6180 [Rint = 0.0529]	6702[Rint=0.0471]
	Completeness to θ = 25.000°	99.7%	99.5%	99.4%	99.2%
	Data / restraints / parameters	3027 / 0 / 124	1556 / 0 / 65	6180 / 0 / 313	6702 / 0 / 135
	Goodness-of-fit	1.172	1.122	1.024	1.035
	Final R indices [I >	Robs = 0.0826,	Robs = 0.0507,	Robs = 0.0525,	Robs = 0.0499, wRobs =
	2σ(I)]	wRobs = 0.2092	wRobs = 0.1258	wRobs = 0.1357	0.1002
	R indices [all data]	Rall = 0.1094, wRall = 0.2600	Rall = 0.0572, wRall = 0.1322	Rall = 0.0652, wRall = 0.1454	Rall = 0.1150, wRall = 0.1364
	Largest diff. peak and hole	4.775 and -4.662 e•Å -3	2.669 and -2.365 e•Å -3	1.963 and -2.542 e•Å -3	2.048 and -3.547 e•Å -3

Table 2 |

 2 Bond length distortion, bond angle variance, optical band-gaps evaluated from the onset of the absorption spectra, energy at maximum PL, full width at half maximum of PL, and average lifetimes of the

		(pPDA)PbBr4	(mPDA)PbBr4	(oPDA)4(PbBr4)2	(mPDA)PbI4
				Pb3Br10•4 H3PO2
	Pb-X-Pb minimum angle (X=Br, I) ( o )	140.59(7)	143.03(4)	--	143.2(3)
	Pb-X-Pb maximum angle (X=Br, I) ( o )	143.56(9)	143.03(4)	--	144.4(2)
	Pb-X-Pb average angles (X=Br, I) ( o )	142.08(8)	143.03(4)	--	143.8(3)
	Bond angle variance 	39.12	45.88	16.54	234.16
	Bond length distortion 	0.008	0.010	0.026	0.005
	Absorption edge (eV)	3.01	3.00	3.44	2.21
	PL emission center (eV)	2.30	2.08	2.58	2.43
	PL FWHM (eV)	0.69	0.73	0.62	0.21
	CIE x	0.34	0.44	0.21	--
	CIE y	0.44	0.46	0.29	--
	CCT	5450	3000	>10000	--

compounds calculated based on the 2D (pPDA)PbBr4, 2D (mPDA)PbBr4, and 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2, respectively.

* The bond length distortion, (Δd) is defined by ∆𝑑 = (

  10• 4H 3 PO 2 compound exhibits a narrow PL peak at 2.58 eV with an FWHM of

0.62 eV. The optical properties of the 1D (oPDA)2Pb3Br10 structures are shown in Figures S2-S3. The broad PL emission for 1D (oPDA)2Pb3Br10 might be attributed to the relatively larger bond length distortion than 1D (oPDA)4(PbBr4)2Pb3Br10•4H3PO2. From time-resolved PL experiments (Figure

Table 3 |

 3 SummaryThese low-dimensional perovskites with short rigid conjugated spacer dications can achieve large-scale tunability in the chromaticity of emission. The chromaticity diagram (CIE) and correlated color temperature (CCT) are obtained using the color calculator software (OSRAM Sylvania, Inc.), as shown in Figure7. Their coordinates deviate from the white point (0.33, 0.33) as shown in Table

	of PL average lifetimes for 2D (pPDA)PbBr4, 2D (mPDA)PbBr4, 1D
	(oPDA)4(PbBr4)2Pb3Br10•4H3PO2 with estimated standard deviations in parentheses.
		τ1	τ2	τ3	τaverage
	(pPDA)PbBr4	0.98	3.07	12.87	3.17 ns
	(mPDA)PbBr4	0.99	3.08	15.89	3.05 ns
	(oPDA)4(PbBr4)2Pb3Br104H3PO2	0.78	2.27	8.99	1.72 ns
	(pPDA)PbBr4 film	0.67	3.01	19.57	3.16 ns
	(mPDA)PbBr4 film	0.81	2.75	15.82	1.93 ns
	(oPDA)4(PbBr4)2Pb3Br104H3PO2 film	0.73	2.64	20.23	1.88 ns

of neat TMS using adamantane as an external reference ( 1 H resonance, 1.82 ppm). 207 Pb experimental shift was calibrated with respect to neat liquid Pb(NO3)2 based on IUPAC recommendation.

Acknowledgments

This work was supported by the National Science Foundation under Grant No. DMR-2019444 (IMOD an NSF-STC). This work used the NUFAB facility of Northwestern University's NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and the Northwestern MRSEC program (NSF DMR-1720139). The MRSEC program (NSF DMR-1720139) at the Materials Research Center, the International Institute for Nanotechnology (IIN), the Keck Foundation, and the State of Illinois through IIN. GNMR gratefully acknowledges financial support from ISITE international mobility grant, IR INFRANALYTICS FR2054, and EU H2020 (Grant 795091) for conducting the ssNMR experiments. P. Fu acknowledges the financial support from the Chinese Academy of Science as a visiting scholar at Northwestern University, USA, 2020RQ036, and fruitful discussion with Chenjian Lin, Yanfeng Yin, and Paige Brown.

Supporting Information

Additional experimental details, materials, and methods; The calculated/experimental XRD patterns, Optical absorption spectra, Steady-state PL spectra and Projected density of states (PDOS) and detailed single-crystal information for all compounds; Electronic structure for the 1D compounds; Temperaturedependent photoluminescence spectra for 2D compounds; Film stability of all compounds, including photographs of different solution.

Accession Codes

CCDC 2182661-2182664 contain the supplementary crystallographic data for this paper.