Nearly one-fold enhancement in photoluminescence quantum yield for isostructural zero-dimensional hybrid antimony(III) bromides by supramolecular interaction adjustments.

Zero-dimensional (0D) organic-inorganic metal halides (OIMHs) hold promise in photoluminescence properties and related applications. Thus far, the photoluminescence quantum yields (PLQYs) of the reported 0D hybrid antimony(III) bromides (HABs) are not as high as those of the chloride analogs; therefore, the improvement of PLQY is an important issue for luminescent HABs. Herein, a supramolecular interaction adjustment strategy to improve the PLQYs of HABs is proposed. Two isostructural 0D HABs that crystallize with different lattice solvent molecules, namely [EtPPh3]2[SbBr5]·EtOH (1·EtOH-Br; EtPPh3 = ethyltriphenylphosphonium; EtOH = ethanol) and [EtPPh3]2[SbBr5]·MeCN (1·MeCN-Br; MeCN = acetonitrile), have been synthesized. Both of them exhibit typical self-trapped exciton (STE) photoluminescence (PL) with broad emission, a large Stokes shift and a long lifetime. They show deviation in deep-red emission peaks (655 nm vs. 661 nm) owing to the difference in the distortion level of [SbBr5]2- anions. Most importantly, 1·EtOH-Br exhibits a nearly one-fold enhancement in PLQY compared to 1·MeCN-Br (18.26% vs. 9.29%). Density functional theory (DFT) calculations, hydrogen bonding analysis and Hirshfeld surface analysis suggest that the PLQY enhancement is due to the structural rigidity improvement brought by hydrogen bonding adjustments between the inorganic [SbBr5]2- anions and solvent molecules. This work provides a new insight into the structure-property relationship study and PLQY improvement for 0D OIMHs.

A deep-red-emission antimony(III) chloride with dual-cations: extremely large Stokes shift due to high [SbCl6] distortion.

Compound [C5mim][Mim]2[SbCl6] (1; [C5mim]+ = 1-pentyl-3-methylimidazolium; [Mim]+ = N-methylimidazolium) with dual cations exhibits the first case of deep-red emission in [SbCl6]3--based 0D OIMHs. Anion distortion due to high disequilibrium of supramolecular interactions is revealed to be responsible for the extremely large Stokes shift of 335 nm and FWHM of 210 nm in the emission.

Selective Luminescence Response of a Zero-Dimensional Hybrid Antimony(III) Halide to Solvent Molecules: Size-Effect and Supramolecular Interactions.

Zero-dimensional (0D) metal halides with solid-state luminescence switching (SSLS) have attracted attention as sensors and luminescent anticounterfeiting. Herein, selective solvent molecule response and accordingly luminescence switching were discovered in 0D [EtPPh3]2[SbCl5] (1, EtPPh3 = ethyltriphenylphosphonium). More than a dozen kinds of solvent molecules have been tested to find out the selection rule for molecule absorption in 1, which is demonstrated to be the size effect of guest molecules. Confirmed by crystal structural analysis, only the solvents with molecular volume less than 22.3 Å3 could be accommodated in 1 leading to the solvatochromic photoluminescence (PL). The mechanism of solvatochromic PL was also deeply studied, which was found to be closely related to the supramolecular interactions between solvent molecules and the host material. Different functional groups of the solvent molecule can affect its strength of hydrogen bonding with [SbCl5]2-, which is crucial for the distortion level of [SbCl5]2- unit and thus results in not only distinct solvatochromic PL but also distinct thermochromic PL. In addition, they all show typical self-trapped exciton triplet emissions. The additional supramolecular interactions from guest molecules can enhance the photoluminescence quantum yield to be as high as 95%.

Boosting Visible-Light-Driven Photocatalytic Hydrogen Production through Sensitizing TiO2 via Novel Nanoclusters.

Improving the light utilization and electron-hole separation efficiency plays a central role in photocatalysis for converting light energy to hydrogen energy. Herein, for the first time, a stable, highly dispersible discrete T4 [Cd3In17Se31]5- cluster is developed as a novel photosensitizer to sensitize TiO2 for photocatalytic hydrogen production. Compared with pristine TiO2 (near zero) and the T4 clusters (19.5 µmol g-1 h-1) that exhibit low hydrogen evolution activities, the T4/TiO2 composite, constructed from traces of 0.127 mol % T4 cluster-sensitized TiO2, exhibits a dramatically improved photocatalytic activity of 328.2 µmol g-1 h-1, highlighting that the photocatalytic efficiency strongly correlates with that of the T4 cluster. In the meantime, the T4/TiO2 composites are highly stable, remaining robust in a long-time test of 50 h for photocatalytic hydrogen production. Ultrafast transient absorption spectroscopy, in combination with electrochemical analyses, steady-state and time-resolved photoluminescence, and density functional theory calculations, indicates that the T4 cluster not only serve as a photosensitizer to absorb visible light but also form a heterojunction between the interface of the T4 cluster and TiO2 to accelerate electron injection. This work highlights the great potential of the stable and highly dispersed discrete metal chalcogenide clusters as high-efficiency photosensitizers for converting solar energy to chemical energy.

Crystalline-Phase-Recognition-Induced Domino Phase Transition and Luminescence Switching for Advanced Information Encryption.

Herein, a new mechanism, namely, crystalline phase recognition (CPR), is proposed for the single-crystal-to-single-crystal (SCSC) transition of metal halides. Chiral ß-[Bmmim]2 SbCl5 (Bmmim=1-butyl-2,3-methylimidazolium) can recognize achiral α-[Bmmim]2 SbCl5 on the basis of a key-lock feature through intercontact of their single crystals, resulting in a domino phase transition (DPT). The concomitant photoluminescence (PL) switching enables observation of the DPT in situ. The liquid eutectic interface, stress-strain transfer, and feasible thermodynamics are key issues for the CPR. DFT calculations and PL measurements revealed that the optical absorption and emission of the isomers mainly originate from [SbCl5 ]2- anions. The structural effects (e.g., supramolecular interactions and [SbCl5 ]2- distortion) on the optical emission are clarified. As a novel type of stimuli response, the CPR-induced DPT and luminescence switching exhibit potential for application in advanced time-resolved information encryption.

Co-luminescence in a zero-dimensional organic-inorganic hybrid antimony halide with multiple coordination units.

Zero-dimensional (0D) organic-inorganic hybrid metal halides (OIMHs) containing multiple halometallate species (HMSs) have received extensive attention due to their capability to achieve multifunctional photophysical characteristics. Herein we report a lead-free 0D-OIMH compound, namely [Emim]8[SbCl6]2[SbCl5] (1, Emim = 1-ethyl-3-methylimidazolium), which is the first crystal containing two distinct mononuclear [SbXn]3-n units in one single structure. The optical absorption, temperature/excitation-variable photoluminescence (PL) and PL decay were studied. 1 exhibits a broad emission centered at 577 nm, which is analyzed to be a combination of the emissions from [SbCl6]3- and [SbCl5]2-. The structural effects including SbSb distances and polyhedral distortion of [SbXn]3-n on the PL of antimony-based 0D-OIMHs are discussed in detail. This work would provide guidance for constructing Sb-based 0D OIMHs composed of multiple halometallate species.

Modulation of the Structure and Photoluminescence of Bismuth(III) Chloride Hybrids by Altering the Ionic-Liquid Cations.

Two bismuth(III) halides hybrids with room-temperature phosphorescence (RTP), namely, [BPy]2[Bi2Cl8(bpym)] (1, BPy = N-butylpyridinium) and [EPy]2[Bi2Cl8(bpym)] (2, EPy = N-ethylpyridinium), were synthesized and characterized. Structural comparison reveals that 1 and 2 possess similar anionic zigzaglike chain of [Bi2Cl8(bpym)]n2n-; however, different packing modes of anion/cations and thus different weak interactions. Interestingly, the utilization of pyridinium cations with different length of alkyl chain could tune the RTP behaviors efficiently. The RTP quantum yield (QY) is increased more than 5-fold from 1 to 2 probably due to more rigid structure of 2 arising from the additional H-bond and anion-π interactions, as confirmed by Hirshfeld surfaces analyses and PLATON calculations. Moreover, additional π-π interactions in 1 could stabilize the triplet excitons, leading to an average lifetime of 1 (11.36 ms at 77 K and 1.407 ms at 298 K) being higher than 2 (0.3618 ms at 77 K and 0.07511 ms at 298 K). Density functional theory (DFT) calculations confirm that inorganic moiety to organic ligand charge-transfer (IOCT) is involved in the phosphorescence process. The present work provides a new sight into the design of RTP metal halides through studying the structure-RTP relationship.

Material Design and Optoelectronic Properties of Three-Dimensional Quadruple Perovskite Halides.

The discovery of new halide perovskite-type structures could favor the exploration of optoelectronic materials, as in the case of double perovskites applied in solar cells, light-emitting diodes, and X-ray detectors. In this work, we propose a strategy for designing quadruple perovskites by heterovalent cation transmutation from double perovskites. Two stable quadruple perovskite halides, i.e., Cs4CdSb2Cl12 and Cs4CdBi2Cl12, with a vacancy-ordered three-dimensional (3D) crystal structure were predicted through symmetry analysis and density functional theory (DFT) calculations. The title perovskite halides are also electronically 3D with direct forbidden bandgaps. Following the indication provided by the DFT results, Cs4CdSb2Cl12 and Cs4CdBi2Cl12 as unique quadruple perovskites were successfully synthesized by a solvothermal method. The steady-state photoluminescence (PL) shows wide emission, while the transient PL exhibits carrier recombination lifetime on the order of microseconds at low temperature. The quadruple perovskite halides provide an alternative platform for promising optoelectronic material design in addition to simple and double perovskites.

[Ba13Sb36Cl34O54]8-: high-nuclearity cluster for the assembly of nanocluster-based compounds.

Herein, we report two nanocluster-based compounds built on an unprecedented cluster [Ba13Sb36Cl34O54]8-, which represents the first example of a discrete alkaline earth (AE)-containing oxochloride cluster and the largest Sb-based oxohalide cluster to date; the proton-conducting property of the compounds was investigated.

Efficient modulation of photoluminescence by hydrogen bonding interactions between inorganic [MnBr4]2- anions and organic cations.

The different hydrogen bond interactions in two organic-inorganic hybrid manganese halide compounds, namely [A]2[MnBr4] (A = N-butyl-N-methylpyrrolidinium ([P14]+) for (1) and N-butyl-N-methylpiperidinium ([PP14]+) for (2)), lead to distinct photoluminescence quantum yields (81% for 1; 55% for 2). Further applications of luminescent 1 are also developed.

Hybrid Chloroantimonates(III): Thermally Induced Triple-Mode Reversible Luminescent Switching and Laser-Printable Rewritable Luminescent Paper.

Two hybrid chloroantimonates(III), [Bzmim]3 SbCl6 (1, Bzmim=1-benzyl-3-methylimidazolium, Tm1 =410 K) and [Bzmim]2 SbCl5 (2, Tm2 =348 K) are presented. 1 exhibits green emission (quantum efficiency of 87.5 %); 2 exhibits blue and red emissions under the irradiation of 310 and 396 nm light, respectively. Using different cooling methods, crystalline 1 and IL@2 (IL=ionic liquid of [Bzmim]Cl) could be generated from the molten 1. Reversible structural and PL transformation triggered by moisture or heat was observed between 1 and IL@2. Such PL switching, combined with the crystallization-induced PL properties of 1 and 2, resulted in the firstly reported triple-mode reversible PL switching, that is, on-off (T>Tm1 ), color switching (T

Designing Polymorphic Bi3+-Containing Ionic Liquids for Stimuli-Responsive Luminescent Materials.

Solid-state luminescent materials that possess reversible fluorescence changes toward external multistimuli are of immense interest because of their potential applications in data storage and sensors. While the recent developments in this field are mainly focused on the π-conjugated organic molecules. Herein two polymorphic luminescent ionic liquid (IL)-based stimuli-responsive materials were designed by the supramolecular assemblies of an organic-decorated chlorobismuthate anion and a rotationally flexible imidazolium cation, namely, α (1)/ß (2)-[Bmmim][BiCl4(2,2'-bpy)] (Bmmim = 1-butyl-2,3-dimethylimidazolium; 2,2'-bpy = 2,2'-bipyridine). Because of the different conformations of the n-butyl chains on the imidazolium cations, tuning of the supramolecular packing structures as well as luminescent colors for 1 and 2 was realized. Single-crystal X-ray diffraction and Hirshfeld surface analyses disclose that the polymorphism-dependent emission may be attributed to the different weak interactions, especially to the π-π interactions between adjacent [BiCl4(2,2'-bpy)]- anions in two compounds. Additionally, compound 2 could be transformed into 1 spontaneously at ambient conditions, which could be triggered by the moisture in the air. Both of the title compounds could detect NH3 vapor selectively through the luminescence "turn-off" method rapidly and reversibly because of the destruction of intermolecular interactions, indicating their stimuli-responsive property toward NH3.

PbX2(OOCMMIm) (X = Cl, Br): photoluminescent organic-inorganic hybrid lead halide compounds with high proton conductivity.

Differences in the electronegativity and hydrophilicity of halogens lead to differences in proton-conducting and photoluminescence properties in hybrid organic-inorganic lead halide compounds of [PbX2(OOCMMIm)]n (X = Cl (1), Br (2), HOOCMMIm = 1-carboxymethyl-3-methylimidazolium).

α- and ß-[Bmim][BiCl4 (2,2'-bpy)]: Two Polymorphic Bismuth-Containing Ionic Liquids with Crystallization-Induced Phosphorescence.

This work reports the syntheses, structures, and luminescence properties of two supramolecular polymorphic compounds composed of a hybrid bismuth(III) chloride anion and an imidazolium cation, namely α- (1) and ß- (2) [Bmim][BiCl4 (2,2'-bpy)] (Bmim=1-butyl-3-methyl imidazolium; 2,2'-bpy=2,2'-bipyridine). They are the first two examples of Bi3+ -containing ionic liquids (ILs). Their different packing modes may be ascribed to the rotational flexibility of the butyl group on the [Bmim]+ cation. A comparative study of the weak intermolecular interactions present in the two polymorphs has been performed by Hirshfeld surface and two-dimensional fingerprint analyses. Investigations of the luminescence properties revealed that crystallization induced greenish-yellow phosphorescence with quantum yields of 26.07 % for 1 and 36.59 % for 2, which are among the highest hitherto reported for hybrid halobismuthate compounds. The difference in phosphorescence may be attributed to the different weak interactions in 1 and 2, especially π-π contacts. This work opens the way to further research on new types of polymorphism-dependent luminescent materials based on a combination of rotationally isomeric IL cations with organic decorated bismuth(III) chloride anions.

A Mg-CP with in Situ Encapsulated Photochromic Guest as Sensitive Fluorescence Sensor for Fe3+/Cr3+ Ions and Nitro-Explosives.

Here we report a fluorescent magnesium coordination polymer (Mg-CP), namely, [CH3-dpb]2[Mg3(1,4-NDC)4(µ-H2O)2(CH3OH)(H2O)]·1.5H2O (1, 1,4-H2NDC = 1,4-naphthalene dicarboxylic acid, dpb = 1,4-bis(pyrid-4-yl)benzene). Compound 1 possesses a three-dimensional (3D) host-guest structure constructed by the 1,4-NDC linkers bridging the linear trinuclear secondary building units of [Mg3(COO)8(µ-H2O)2]. The dpb molecules were in situ reacted with CH3OH resulting in photochromic cations of [CH3-dpb]+ that acted as guests located in the channels parallel to the b-axis. Photoluminescence (PL) studies indicated that 1 showed a strong green emission demonstrating sensitive fluorescence sensing of Fe3+/Cr3+ metal ions and nitro-explosive compounds. Compound 1 represents the first PL Mg-CP as a fluorescent probe for detecting metal ions. Moreover, because of the in situ encapsulation of photochromic [CH3-dpb]+ guests, 1 exhibited reversible photochromic behavior.