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

Glass Disorder Modulated Luminescence in Zero-Dimensional Antimony-Chloride Coplanar Dimers for Optical Anti-counterfeiting

Zero-dimensional metal halides have received wide attention due to their structural diversity, strong quantum confinement, and associated excellent photoluminescence properties. A reversible and tunable luminescence would be desirable for applications such as anti-counterfeiting, information encryption, and artificial intelligence. Yet, these materials are underexplored, with little known about their luminescence tuning mechanisms. Here we report a pyramidal coplanar dimer, (TBA)Sb2Cl7 (TBA = tetrabutylammonium), showing broadband emission wavelength tuning (585-650 nm) by simple thermal treatment. We attribute the broad color change to structural disorder induced by varying the heat treatment temperatures. Increasing the heating temperature transitions the material from long-range ordered crystalline phase to highly disordered glassy phase. The latter exhibits stronger electron-phonon coupling, enhancing the self-trapped exciton emission efficiency. The work provides a new material platform for manifold optical anti-counterfeiting applications and sheds light on the emission color tuning mechanisms for further design of stimuli-responsive materials.

TPP-based conjugates: potential targeting ligands

Mitochondria are one of the major sources of energy as well as regulators of cancer cell metabolism. Thus, they are potential targets for the effective treatment and management of cancer. Research has explored triphenylphosphonium (TPP) derivatives as potent cancer-targeting ligands because of their lipophilic nature and mitochondrial affinity. In this review, we summarize the utility of TPP-based conjugates targeting mitochondria in different types of cancer and other diseases, such as neurodegenerative and cardiovascular disorders. Such conjugates offer versatile therapeutic potential by modulating membrane potential, influencing reactive oxygen species (ROS) production, and coupling of molecular modifications (such as ATP metabolism and energy metabolism). Thus, we highlight TPP conjugates as promising mitochondria-targeting agents for use in targeted drug delivery systems.

Rigid Phase Formation and Sb3+ Doping of Tin (IV) Halide Hybrids toward Photoluminescence Enhancement and Tuning for Anti-Counterfeiting and Information Encryption

Multi-excitonic emitting materials in luminescent metal halides are emerging candidates for anti-counterfeiting and information encryption applications. Herein, ATPP2SnCl6 (ATPP=acetonyltriphenylphosphonium) phase was designed and synthesized by rationally choosing emissive organic reagent of ATPPCl and non-toxic stable metal ions of Sn4+, and Sb3+ was further doped into ATPP2SnCl6 to tune the photoluminescence with external self-trapped excitons emission. The derived non-toxic ATPP2SnCl6 shows multi-excitonic luminescent centers verified by optical study and differential charge-density from density functional theory calculations. Incorporation of Sb3+ dopants and the increasing concentrations induce the efficient energy transfer therein, thus enhancing photoluminescence quantum yield from 5.1 % to 73.8 %. The multi-excitonic emission inspires the creation of information encryption and decryption by leveraging the photoluminescence from ATPPCl to ATPP2SnCl6 host and ATPP2SnCl6 : Sb3+. This study facilitates the anti-counterfeiting application by employing solution-processable luminescent metal halides materials with excitation-dependent PL properties.

Manipulating Chiroptical Activities in 0D Chiral Hybrid Manganese Bromides by Solvent Molecular Engineering

0D hybrid metal halides (0D HMHs) with fully isolated inorganic units provide an ideal platform for studying the correlations between chiroptical activities and crystal structures at atomic levels. Here, through the incorporation of different solvent molecules, a series of 0D chiral manganese bromides (RR/SS-C20H28N2)3MnBr8·2X (X = C2H5OH, CH3OH, or H2O) are synthesized to elucidate their chiroptical properties. They show negligible circular dichroism signals of Mn absorptions due to C2v-symmetric [MnBr4]2- tetrahedra. However, they display distinct circularly polarized luminescence (CPL) signals with continuously increased luminescence asymmetry factors (glum) from 10-4 (X = C2H5OH) to 10-3 (X = H2O). The increased glum value is structurally revealed to originate from the enhancement of [MnBr4]2- tetrahedral bond-angle distortions, due to the presence of different solvent molecules. Furthermore, (RR/SS-C20H28N2)MnBr4·H2O enantiomers with larger bond-angle distortions of [MnBr4]2- tetrahedra are synthesized based on hydrobromic acid-induced structural transformation of (RR/SS-C20H28N2)3MnBr8·2H2O enantiomers. Therefore, such (RR/SS-C20H28N2)MnBr4·H2O enantiomers exhibit enhanced CPL signals with |glum| up to 1.23 × 10-2. This work provides unique insight into enhancing chiroptical activities in 0D HMH systems.

Fabrication strategies for chiral self-assembly surface

Chiral self-assembly is the spontaneous organization of individual building blocks from chiral (bio)molecules to macroscopic objects into ordered superstructures. Chiral self-assembly is ubiquitous in nature, such as DNA and proteins, which formed the foundation of biological structures. In addition to chiral (bio) molecules, chiral ordered superstructures constructed by self-assembly have also attracted much attention. Chiral self-assembly usually refers to the process of forming chiral aggregates in an ordered arrangement under various non-covalent bonding such as H-bond, π-π interactions, van der Waals forces (dipole-dipole, electrostatic effects, etc.), and hydrophobic interactions. Chiral assembly involves the spontaneous process, which followed the minimum energy rule. It is essentially an intermolecular interaction force. Self-assembled chiral materials based on chiral recognition in electrochemistry, chiral catalysis, optical sensing, chiral separation, etc. have a broad application potential with the research development of chiral materials in recent years.

Zero-dimensional hybrid tin halides with stable broadband light emissions

Considering the instability and toxicity of 3D Pb-based perovskite nanocrystals, lead-free low-dimensional organic-inorganic hybrid metal halides have attracted widespread attention as potential substitutes. Herein, two new tin-based 0D halides [H4BAPP]SnBr5·Br and [H4BAPP]SnCl5·Cl·H2O (BAPP = 1,4-bis(3-aminopropyl)piperazine) were synthesized successfully based on [SnX5]3- as an emission center. Typically, [H4BAPP]SnBr5·Br and [H4BAPP]SnCl5·Cl·H2O display broadband yellow and yellow-green light emissions originating from the radiative recombination of self-trapped excitons (STEs). The photoluminescence quantum yields (PLQYs) of the two compounds were calculated to be 19.27% and 2.36%, respectively. Furthermore, the excellent chemical and thermal stability and broadband light emissions reveal their potential application in solid-state white lighting diodes.

Supramolecular-Interactions-Modulated Photoluminescence in Indium Bromide-Based Isomers

Here, two isomeric ionic zero-dimensional indium bromide crystals of α (1)/β (2)-[OPy][InBr4(Phen)] (OPy = N-octylpyridinium; Phen = 1,10-phenanthroline) have been isolated simply by changing the cooling conditions in solvothermal syntheses. Structural comparisons indicate their different supramolecular interactions, which can be confirmed by Hirshfeld surface analyses. The crystal 2 has additional hydrogen bonds and π-π interactions; as a result, the more compact stacking of 2 could result in a 10-fold higher photoluminescence (PL) quantum yield (PLQY) than that of 1. Density functional theory calculations confirm the electron transition from the inorganic moiety to the organic ligand, which provides a further understanding of the optical process. This work provides a new idea for designing PL indium-based halides by understanding the structure-PL relationship.

Ultralow-loss Optical Waveguides through Balancing Deep-Blue TADF and Orange Room Temperature Phosphorescence in Hybrid Antimony Halide Microstructures

Harnessing the potential of thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) is crucial for developing light-emitting diodes (LEDs), lasers, sensors, and many others. However, effective strategies in this domain are still relatively scarce. This study presents a new approach to achieving highly efficient deep-blue TADF (with a PLQY of 25 %) and low-energy orange RTP (with a PLQY of 90 %) through the fabrication of lead-free hybrid halides. This new class of monomeric and dimeric 0D antimony halides can be facilely synthesized using a bottom-up solution process, requiring only a few seconds to minutes, which offer exceptional stability and nontoxicity. By leveraging the highly adaptable molecular arrangement and crystal packing modes, the hybrid antimony halides demonstrate the ability to self-assemble into regular 1D microrod and 2D microplate morphologies. This self-assembly is facilitated by multiple non-covalent interactions between the inorganic cores and organic shells. Notably, these microstructures exhibit outstanding polarized luminescence and function as low-dimensional optical waveguides with remarkably low optical-loss coefficients. Therefore, this work not only presents a pioneering demonstration of deep-blue TADF in hybrid antimony halides, but also introduces 1D and 2D micro/nanostructures that hold promising potential for applications in white LEDs and low-dimensional photonic systems.

Dual Monomeric Inorganic Units Constructed Bright Emissive Zero-Dimensional Antimony Chlorides with Solvent-Induced Reversible Structural Transition

A5M2X11 and A3M2X9 families (A = monovalent organic cation; M = trivalent metal; X = halogen) are receiving increasing attention because of their combination of easy solution processability and superior ferroelectricity properties. However, synthesizing highly efficient A5M2X11 and A3M2X9-type fluorophores with multiple monomeric inorganic units and achieving their structural interconversion remains challenging. Here, we report two novel zero-dimensional (0D) antimony halides, (C10H16N)5Sb2Cl11·C2H3N (1) and (C10H16N)3Sb2Cl9 (2), which not only contain two distinct [SbXn]3-n units but also have excellent orange (590 nm) and yellow-green emission (540 nm) with high PLQY of 17.7% and 31.5%, respectively. Interestingly, a reversible structural conversion could be triggered by acetonitrile steam stimulation, accompanied by luminescence switching properties. This work not only enriches the structure of hybrid Sb-based halides but also provides the possibility of well-known A5M2X11 and A3M2X9 families as structural transformation materials.

Reversible Luminescent Switching Induced by Heat/Water Treatment in a Zero-Dimensional Hybrid Antimony(Ⅲ) Chloride

Recently zero-dimensional (0-D) inorganic-organic metal halides (IOMHs) have become a promising class of optoelectronic materials. Herein, we report a new photoluminescent (PL) 0-D antimony(III)-based IOMH single crystal, namely [H₂BPZ][SbCl₅]·H₂O (BPZ = benzylpiperazine). Photophysical characterizations indicate that [H₂BPZ][SbCl₅]·H₂O exhibits singlet/triplet dual-band emission. Density functional theory (DFT) calculations suggest that [H₂BPZ][SbCl₅]·H₂O has the large energy difference between singlet and triplet states, which might induce the dual emission in this compound. Temperature-dependent PL spectra analyses suggest the soft lattice and strong electron-phonon coupling in this compound. Thermogravimetric analysis shows that the water molecules in the lattice of the title crystal could be removed by thermal treatment, giving rise to a dehydrated phase of [H₂BPZ][SbCl₅]. Interestingly, such structural transformation is accompanied by a reversible PL emission transition between red light (630 nm, dehydrated phase) and yellow light (595 nm, water-containing phase). When being exposed to an environment with 77% relative humidity, the emission color of the dehydrated phase was able to change from red to yellow within 20 s, and the red emission could be restored after reheating. The red to yellow emission switching could be achieved in acetone with water concentration as low as 0.2 vol%. The reversible PL transition phenomenon makes [H₂BPZ][SbCl₅]·H₂O a potential material for luminescent water-sensing.

Rational Design of a Super-Alkali Compound with Reversible Photoluminescence

The zero-dimensional (0D) (H₅O₂)(C₄H₁₄N₂S₂)₂BiCl₈: Sb³⁺ single crystal is obtained by the cooling crystallization method. Surprisingly, this compound shows reversible photoluminescence (PL) upon H₅O₂⁺Cl^- removal and insertion. To be specific, the release of H₅O₂⁺Cl^- resulted in red-orange emission with a very low photoluminescence quantum yield (PLQY). While on the reuptake of it, a bright yellow emission with a nearly 10-fold increase of PLQY was observed. Density functional theory (DFT) calculations and temperature-dependent PL experiments reveal that significant [SbCl₆]^3- octahedron distortion induced by guest (H₅O₂⁺Cl^-) removal at the ground state, especially at the excited state, is responsible for the disparate PL performance. Encouragingly, we also found that (C₄H₁₄N₂S₂)₂BiCl₇: Sb³⁺ exhibits a fast response (<3 s) to dilute hydrochloric acid with naked-eye perceivable PL color changes, rendering it a potential sensing material for hydrochloric acid.

Multiple Light Source-Excited Organic Manganese Halides for Water-Jet Rewritable Luminescent Paper and Anti-Counterfeiting

Rewritable luminescent paper is particularly crucial, considering the ultrahigh paper consumption and confidential information security, but a highly desirable stimuli-responsive smart luminescent material with excellent water solubility has rarely been studied. Herein, a new type of rewritable paper made by highly efficient green light emissive zero-dimensional (0D) organic manganese halides is rationally designed by virtue of the reversible photoluminescence (PL) off-on switching. Specifically, the green emission can be linearly quenched by water vapor in a wide humidity range and again recovered in a dry atmosphere, which make it a smart hydrochromic PL off-on switching and humidity sensor. Benefiting from the reversible luminescence off-on switch and excellent water solubility, rewritable luminescent paper is realized through water-jet security printing technology on 0D halide-coated commercial paper with high resolution. The printed/written information can be easily cleaned by slight heating with outstanding "write-erase-write" cycle capabilities. In addition, multiple light source-induced coincident green light emissions further provide convenience to realize anti-counterfeiting, encryption and decryption of confidential information, and so forth. This work highlights the superiority of dynamic ionic-bonded 0D organic manganese halides as reversible PL switching materials in rewritable luminescent paper, high-security-level information printing, storage and protection technologies, and so forth.

Synthetic-Method-Dependent Antimony Bromides and Their Photoluminescent Properties

Recently, excellent optical properties of low-dimensional organic-inorganic metal halides, stemming from their tunable structure and optoelectronic properties, have been demonstrated. The synthetic method is critical because it is highly related to the structure and properties of the halide. Herein, we obtain two different antimony bromides, (Bmpip)₂SbBr₅ and (Bmpip)₃Sb₂Br₉, which both possess the P2₁/c space group having different crystal structures, and this confirms the important influence of synthesis on the single-crystal structure. (Bmpip)₂SbBr₅ contains Bmpip⁺ and [SbBr₅]^2- pyramids, and (Bmpip)₃Sb₂Br₉ consists of Bmpip⁺ and Sb-based dimers [Sb₂Br₉]^3-. Under 400 nm excitation, (Bmpip)₂SbBr₅ exhibits a 640 nm orange emission with a quantum yield of ∼11.5% owing to Sb 5s² electron luminescence. A diode was fabricated by (Bmpip)₂SbBr₅ and commercial phosphors and showed a high color render index of 92. Our work reveals the effect of the preparation method on the crystal structure. A luminescent material was finally identified.

Luminescent Organic-Inorganic Hybrid Metal Halides: An Emerging Class of Stimuli-Responsive Materials

Luminescent organic-inorganic metal halides (OIMHs) are well known as a new materials family in recent years. Novel materials and applications of luminescent OIMHs have been explored by changing either the organic component or the metal halide species. Thereinto, the stimuli-responsive (SR) phenomena in OIMHs have drawn much attention recently, for not only their attractive application potential but also the helpfulness in understanding the stability of OIMHs to the external environment. Herein, the luminescent OIMHs that are sensitive to external stimuli including contact, pressure, mechanical grinding, light, heat, and gas molecules, are reviewed, with an emphasis on analyses of the structural change during the SR process. The applications of SR luminescent OIMHs in widespread fields, including gas sensing, information encryption, and rewritable luminescent paper are summarized. Finally, the challenges that deserve to be further explored in this research field are discussed, which provides certain guidance for the future study of SR luminescent OIMHs.

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.