Multi-Light-Responsive Upconversion-and-Downshifting-Based Circularly Polarized Luminescent Switches in Chiral Metal-Organic Frameworks

Temperature and Solvent Dual Switch Photochromic Chiral Ionic Hydrogen-Bonded Organic Framework for Circularly Polarized Luminescence and Advanced Encryption

Multi-response encryption materials with temperature control and time resolution have attracted widespread attention due to their unique response characteristics and higher application security. The design and development of photochromic crystalline materials with multiple stimulus responses remain challenging. In this study, we report a pair of responsive photochromic chiral ionic hydrogen-bonded organic framework (iHOF) R/S-iHOF-19, controlled by both temperature and solvent through charge-assisted synthesis. The chromophore tetrakis(4-sulfophenyl)ethylene (H4TPE) acts as an electron donor and (1R/S,2R/S)-1,2-diphenylethylenediamine (R/S-DPEN) as an electron acceptor and chiral source. Water and methanol molecules connect the donor and acceptor and interact to build a 3D supramolecular framework. Notably, water and methanol molecules form independent hydrogen-bonding channels within the iHOF structural framework, providing a transfer path for the photoinduced electrons. Surprisingly, the formation of a continuous chiral supramolecular framework by R/S-DPEN while generating photo-induced radicals under ultraviolet (UV) irradiation at -20 °C imparts excellent circularly polarized luminescence (CPL) properties to R/S-iHOF-19. The glum values reach -1.8 × 10-3 and +3.75 × 10-3, respectively, and show an enhancement of the circular polarization of light with decreasing temperature. This CPL with unique low-temperature stimulus-responsive photochromism provides new guidance and perspectives for the development of information security and multiple encryption materials.

Chiral dual-annihilator model for controllable photon upconversion and multi-dimensional optical modulation

Triplet-triplet annihilation photon upconversion seeks efficient conversion of low-energy photons to high-energy emission. However, the triplet-triplet annihilation photon upconversion system faces limitations in emission gamut because efficient triplet-triplet energy transfer between sensitizer and annihilator relies on triplet energy matching, making it challenging to realize multi-channel luminescence and multi-dimensional optical control. Here, to overcome this barrier, we propose a chiral dual-annihilator model, which mitigates the restriction of energy matching and achieves facile manipulation of circularly polarized luminescence through a dual-channel triplet-triplet energy transfer process. A theoretical equation for quantifying the overall triplet-triplet energy transfer efficiency and the energy flow between the sensitizer and two kinds of annihilators is proposed. Its accuracy is demonstrated by fine-controlling the emission bandwidth of triplet-triplet annihilation photon upconversion (average error less than 4.5%) in the experimental aspect. In addition, by introducing chiral liquid crystals, the dual-annihilator model achieves data coding and multi-dimensional optical encryption applications. This dual-annihilator model deepens the understanding of energy flow and lays the foundation for accurate, multidimensional modulation of photon upconversion.

Controlling Circularly Polarized Luminescence Enabled by Chirality and Energy Transfer from Optimized Chiral Molecules to Quantum Dots

Chirality transfer/amplification and energy transfer in artificial assembly systems are longstanding challenges inspired by biological systems. In particular, controlling intercomponent interactions to engineer CPL-active materials in multicomponent chiral coassemblies remains difficult. Here, we report the simultaneous realization of chirality and energy transfer in self-assembled hybrid systems comprising quantum dots with high photoluminescence quantum yield and organic molecules featuring aggregation-induced emission (AIE). Three chiral AIE molecules based on the tetraphenylethylene core, differing in the number and/or position of alkyl chains, were designed and synthesized. These structural variations led to distinct self-assembled morphologies, including helical fibrils, fibril bundles, and ribbons. Co-assembly with luminescent CdSe/CdS nanorods yielded organic-inorganic hybrid nanocomposites, where chirality transfer from the organic molecules to the nanorods strongly depended on the molecular structure. In parallel, efficient energy transfer from chiral donors to the nanorod acceptors was observed across all systems. Notably, the synergistic action of both chirality and energy transfer enabled the construction of CPL-active materials with high luminescence asymmetry factors. This work presents a strategy for designing chiroptical systems with enhanced chiroptical performance.

High-Performance White Circularly Polarized Photoluminescence and Electroluminescence from Multi-Emission Enantiomers

A pair of multi-emission enantiomers, (R)-DO-PSeZ and (S)-DO-PSeZ, was designed and synthesized by integrating Se-induced conformationally isomeric donors with a chiral carbonyl-containing acceptor into a unified molecular framework. The enantiomers showed white emission with blue, yellow and red multi-emission bands in solution and film at CIE coordinates of (0.39, 0.35) and (0.33, 0.34), respectively. Doped film of the enantiomers achieved a high photoluminescence quantum yield of 42 %, accompanied by mirror-image white circularly polarized photoluminescence (WCPPL) signals with a |gPL| value of 2.6×10-3. Moreover, the enantiomers also showed white circularly polarized electroluminescence (WCPEL) in organic light-emitting diodes with CIE coordinates of (0.29, 0.33) and EQEmax of 3.1 %. Notably, this work represents the first single-molecule multi-emission WCPL materials and achieved the highest performance for white OLEDs based on single-molecule organic materials with phosphorescent properties. Furthermore, leveraging Bragg reflection from dual-layer cholesteric liquid crystals, the enantiomers achieved |gPL| and |gEL| values of 1.85 and 1.88, respectively, marking the highest reported values for WCPPL and WCPEL to date.

Challenges and Opportunities of Upconversion Nanoparticles for Emerging NIR Optoelectronic Devices

Upconversion nanoparticles (UCNPs), incorporating lanthanide (Ln) dopants, can convert low-energy near-infrared photons into higher-energy visible or ultraviolet light through nonlinear energy transfer processes. This distinctive feature has attracted considerable attention in both fundamental research and advanced optoelectronics. Challenges such as low energy-conversion efficiency and nonradiative losses limit the performance of UCNP-based optoelectronic devices. Recent advancements including optimized core-shell structures, tailed Ln-doping concentration, and surface modifications show significant promise for improving the efficiency and stability. In addition, combining UCNPs with functional materials can broaden their applications and improve device performance, paving the way for the innovation of next-generation optoelectronics. This paper first categorizes and elaborates on various upconversion mechanisms in UCNPs, focusing on strategies to boost energy transfer efficiency and prolong luminescence. Subsequently, an in-depth discussion of the various materials that can enhance the efficiency of UCNPs and expand their functionality is provided. Furthermore, a wide range of UCNP-based optoelectronic devices is explored, and multiple emerging applications in UCNP-based neuromorphic computing are highlighted. Finally, the existing challenges and potential solutions involved in developing practical UCNPs optoelectronic devices are considered, as well as an outlook on the future of UCNPs in advanced technologies is provided.

Single-Site Iridium Catalyst on Metal-Organic Framework as Light-Responsive Oxidase-Like Nanozyme with High Stability for Colorimetric Detection of Antioxidant Capacity

The design and synthesis of advanced artificial enzymes are essential for developing promising surrogates for natural enzymes. Herein, we reported an efficient and facile strategy for the synthesis of a single-site iridium catalyst on a metal-organic framework (UiO-67@Ir) as a light-responsive oxidase-like nanozyme, in which UiO-67 was utilized as a host template and the iridium(III) complex was utilized as a photosensitizer with a light-responsive property. A single-site iridium catalyst on UiO-67@Ir by the coordination of the Ir (III) complex with the nitrogen atom of UiO-67 is confirmed by X-ray photoelectron spectroscopy and aberration-corrected atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. The UiO-67@Ir possesses remarkable light-responsive oxidase-like activity and good cycle and storage stability. Excellent catalytic activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) was obtained with 0.204 mM of Michaelis-Menten constant (Km) due to its large surface areas and abundant active sites. TMB was oxidized by UiO-67@Ir in the presence of O2 under light irradiation through the formation of both •OH and O2•- by type I photosensitization processes (electron transfer) and the formation of 1O2 by type II photosensitization processes (energy transfer). Moreover, a sensitive colorimetric method was developed for the detection of antioxidants with a detection limit of 0.6, 0.5, and 0.3 μM for ascorbic acid, glutathione, and cysteine, respectively. The total antioxidant capacity in fruit and drink samples were analyzed with desirable results. This study not only enlightens the novel nanozyme designing strategies but also suggests its good analytical performance in colorimetric sensing.

Chiral Cross-Linked Covalent Organic Framework Films for Highly Sensitive Circularly Polarized Luminescence Probing

The development of covalent organic framework (COF) films featuring circular polarization luminescence (CPL) probing remains a formidable challenge. Herein, we developed a chiral cross-linked COF film to obtain uniform and dense chiral COF films (chirCOFilm) possessing highly sensitive CPL probing for enantiomers. The axial chiral cross-linkers (R-/S-BBNA) are initially introduced into the channels of a COF film (COFilm/R-BBNA or COFilm/S-BBNA) by the vapor-assisted epitaxial method. Then, olefin groups in R-/S-BBNA and COF layers undergo a chiral cross-linking reaction under UV irradiation, forming a chirCOFilm. The obtained chirCOFilms have strong chirality with mirror images, fluorescence discoloration, and intense CPL properties. A multitude of rich chiral photopatterns and chirCOFilm/PDMS flexible films are prepared taking advantage of the photochromic properties of the chirCOFilms during UV illumination, showing the potential application of advanced anticounterfeiting. More importantly, the chirCOFilms realize highly sensitive CPL probing of phenethylamine enantiomers at 5% concentration, which can hardly be achieved from their corresponding fluorescence probing. This study not only provides a new strategy for preparing chiral COF films using chiral cross-linking reaction but also opens a new avenue for achieving highly sensitive probing of enantiomers though CPL.

Chiral Rotaxane-Branched Dendrimers as Relays in Artificial Light-Harvesting Systems with Boosted Circularly Polarized Luminescence

Starting from AIEgen-functionalized chiral [2]rotaxane building block, we have successfully synthesized a new class of chiral rotaxane-branched dendrimers through controllable divergent strategy for the first time, based on which novel chiral artificial light-harvesting systems (LHSs) were successfully constructed in aqueous phase by sequentially introducing achiral donor and acceptor. More importantly, accompanied by the two-step Förster resonance energy transfer (FRET) process in the resultant artificial LHSs, the sequentially amplified circularly polarized luminescence (CPL) performances were achieved, highlighting that the chiral rotaxane-branched dendrimers could serve as excellent relay for both energy transfer and chirality transmission. Impressively, compared with the sole chiral rotaxane-branched dendrimers, the dissymmetry factors (glum) values of the resultant artificial LHSs were amplified by one order of magnitude up to 0.038, enabling their further applications in information storage and encryption. The proof-of concept study provides not only a feasible approach for the efficient amplification of CPL performances but also a novel platform for the construction of novel chiral luminescent materials.

Solution-Processable Metal-Organic Framework Featuring Highly Tunable Dynamic Aggregation States

The limited processability of metal-organic frameworks (MOFs) is hindered flexibility in the manipulation of their aggregation state and applications. Therefore, achieving highly processable MOFs is of great significance but a challenging goal. Herein, a facile strategy is presented for achieving the construction of solution-processable Mg-based MOF, NKU-Mg-1, allowing for dynamic control of the aggregation state through dynamic self-assembly (DySA) process and reversible circularly polarized luminescence (CPL) switcher modulation. Notably, micron-sized crystals of NKU-Mg-1 can be readily dispersed in water to form nano-sized colloids, triggered by the dynamic COO-Mg coordination bonding interruption by the competitive H2O-Mg bonding. Accordingly, the aggregation state of the colloid MOF can be readily tuned from 50-80 nm up to 1000 nm, in turn enabling control of aggregation-dependent emission. Specially, the solid-phase aggregation can be controlled via structural transitions between 3D NKU-Mg-1-rec-1 and 2D NKU-Mg-1-rec-2 nano-crystals, as confirmed by 3D electron diffraction. Furthermore, benefiting from its highly dynamic tunable aggregation nature, the rational incorporation of the chiral module confers significant CPL activity (glum up to 0.01). Importantly, controllable dynamic aggregation enables reversible switching of the CPL activity by precisely regulating the aggregation states. The solution-processable and dynamic aggregation-tunable features endow it highly promising for applications.

Photo-Induced Radical Generation of Supramolecular Gel with Sign-Inverted and White-Light Circularly Polarized Luminescence

The realization of persistent luminescence and in particular circularly polarized luminescence (CPL) of organic radicals remains a challenge due to their sensitivity to oxygen at ambient conditions and elusive excited state chirality control. Here, it is reported that UV-irradiation on a supramolecular gel from a chiral triarylamine derivative, TPA-Ala, led to the formation of luminescent radicals with bright CPL. TPA-Ala can form an organogel in chloroform with blue emission and supramolecular chirality as demonstrated by both CD and CPL signals. Upon UV 365 nm irradiation, an emission color change from blue to cyan is observed due to the formation of photo-induced radicals. Interestingly, it is found that the supramolecular gel radicals showed stable luminescence with a lifetime ≈ 10 days in dark environments and inverted CPL, which represents a scarce example with persistent CPL from doublet-state due to oxygen isolation ability of the gel network. Furthermore, doping a guest dye, Rhodamine B (RhB), into the supramolecular gel (RhB/TPA-Ala = 30% in molar ratio) successfully obtained a transient white-light CPL through the superposition of photo-induced radical and guest dye emissions. This work provides a useful methodology for the fabrication of radical-based CPL materials via a supramolecular assembly approach.

Mechanically Twisting-Induced Top-Down Chirality Transfer for Tunable Full-Color Circularly Polarized Luminescent Fibers

Circularly polarized luminescence (CPL) materials with rich optical information are highly attractive for optical display, information storage, and encryption. Although previous investigations have shown that external force fields can induce CPL activity in nonchiral systems, the unique role of macroscopic external forces in inducing CPL has not been demonstrated at the level of molecule or molecular aggregate. Here, a canonical example of CPL generation by mechanical twisting in an achiral system consisting of a polymer matrix with embedded fluorescent molecules is presented. By carefully adjusting the twisting parameters in time and space, in conjunction with circular dichroism (CD), CPL, and 2D wide-angle X-ray scattering (2D WAXS) studies, a twisting-induced top-down chiral transfer mechanism derived from the molecular-level asymmetric rearrangement of fluorescent units is elucidated within polymers under external torsional forces. This top-down chiral transfer provides a simple, scalable, and versatile mechanical twisting strategy for the fabrication of CPL materials, allowing for fabricating full-color and handedness-tunable CPL fibers, where the macroscopic twist direction determines the CPL handedness. Moreover, the weavability of CPL fibers greatly extend their applications in anti-counterfeit encryption, as demonstrated by using embroidery techniques to design multilevel encryption patterns.

Reticulating Crystalline Porous Materials for Asymmetric Heterogeneous Catalysis

Asymmetric catalysis is essential for addressing the increasing demand for enantiopure compounds. Recent advances in reticular chemistry have demonstrated that metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) possess highly regular porous architectures, exceptional tunability, and the ability to incorporate chiral functionalities through their open channels or cavities. These characteristics make them highly effective and enantioselective catalysts for a wide range of asymmetric transformations. The chiral microenvironments within these frameworks facilitate precise control over reactant orientation and transition states, enhancing both catalytic activity and enantioselectivity, thereby offering significant advantages over traditional systems. This review overviews recent developments in chiral MOFs (CMOFs) and chiral COFs (CCOFs), focusing on their design strategies, and synthetic methods, and highlights the structure-property relationships that connect key structural features to asymmetric catalytic performance. Additionally, the current challenges and future prospects in this field are addressed, highlighting the pivotal role of reticular chemistry in the creation of chiral porous materials. It is anticipated that this review will inspire further research into the application of crystalline porous materials in asymmetric catalysis and promote the rational design of novel chiral heterogeneous catalysts for industrial use.

Radiative energy transfer enabling upconverted circularly polarized persistent luminescence for multilevel information encryption

Optically active persistent luminescent materials are highly promising for anticounterfeiting applications due to their distinct luminescent features and the ability to display unique optical polarization properties. Despite significant progress in the development of circularly polarized persistent luminescence (CPPL) materials, the fabrication of upconverted circularly polarized persistent luminescence (UC-CPPL) materials remains a considerable challenge. In this study, we present an efficient strategy to construct UC-CPPL materials by embedding upconversion nanoparticles (UCNPs) and phosphors into chiral nematic liquid crystals (N*LC). The system operates through a radiative energy transfer mechanism between the UCNPs and phosphors. Upon excitation by low-energy near-infrared light (980 nm), the UCNPs emit high-energy ultraviolet light, which is effectively transferred to the phosphors, resulting in the emission of circularly polarized persistent visible light. By precisely tuning the photonic bandgap of the chiral N*LC, the UC-CPPL luminescence dissymmetry factor (gUC-CPPL) can be amplified to approximately 0.6. The concept of UC-CPPL was realized through the integration of three advanced optical properties: circularly polarized luminescence, long persistent luminescence, and upconversion luminescence. This integration enables more sophisticated and secure information encryption. The incorporation of upconversion materials facilitates the controlled concealment and selective release of encrypted information, while the multileveled encoding scheme further enhances the complexity and security of the encryption process, achieving true information hiding and encryption.

Reversible Circularly Polarized Luminescence Inversion and Emission Color Switching in Photo-Modulated Supramolecular Polymer for Multi-Modal Information Encryption

Constructing circularly polarized luminescence (CPL) materials that exhibit dynamic handedness inversion and emissive color modulation for multimodal information encryption presents both a significant challenge and a compelling opportunity. Here, we have developed a pyridinethiazole acrylonitrile-cholesterol derivative (Z-PTC) that exhibits wavelength-dependent photoisomerization and photocyclization, enabling dynamic handedness inversion and emissive color modulation in supramolecular assemblies with decent CPL activity. Coordination with Ag+ ions form the Z-PTC Ag supramolecular polymer (SP1), which assembles into nanotubes displaying enhanced positive yellow-green CPL. Irradiation at 454 nm transforms SP1 into nanospheres of a mixture supramolecular polymer (SP2) of Z/E-PTC Ag, displaying inverted supramolecular chirality and emitting negative orange-yellow CPL. Reheating SP2 to 343 K restores the original nanotube structure via excellent reversible photoisomerization. Exposure to 365 nm light also induces CPL inversion from positive to negative and triggers morphological changes from SP1 to SP2. Prolonged irradiation causes further transformation into irregular supramolecular aggregate, shifting the emission color to blue and eliminating CPL. These dynamic properties of the multicolor CPL system, including reversible handedness inversion, can also be realized in the semisolid state, exhibiting promising potential for multimodal information encryption applications with enhanced security and complexity.

Pathway-directed recyclable chirality inversion of coordinated supramolecular polymers

It remains challenging to elucidate the fundamental mechanisms behind the dynamic chirality inversion of supramolecular assemblies with pathway complexity. Herein, metal coordination driven assembly systems based on pyridyl-conjugated cholesterol (PVPCC) and metal ions (Ag+ or Al3+) are established to demonstrate pathway-directed, recyclable chirality inversion and assembly polymorphism. In the Ag(I)/PVPCC system, a competitive pathway leads Ag-Complex to form either kinetically controlled supramolecular polymer (Ag-SP I) or thermodynamically favored Ag-SP II, accompanied by reversible chiroptical inversion. Conversely, the Al(III)/PVPCC system displays a solvent-assisted consecutive pathway: the Al-Complex initially forms ethanol-containing Al-SP II, and subsequently converts into ethanol-free Al-SP I with opposite chiroptical performance upon thermal treatment. Moreover, stable chirality inversion in the solid state enables potential dynamic circularly polarized luminescence encryption when Ag(I)/PVPCC is co-assembled with thioflavin T. These findings provide the guidance for the dynamic modulation of chirality functionality in supramolecular materials for applications in information processing, data encryption, and chiral spintronics.

Chiral Metal-Organic Framework Films with Ordered Macropores for Enantioselective Analysis of Proteins

Chiral film-based sensors show great promise for discriminating between enantiomers due to their miniaturization and low power consumption. However, their practical use is hindered by the trade-off between enantioselectivity and mass transfer capability, especially concerning biomacromolecules such as proteins. In this work, we present an effective and straightforward method for creating highly organized macropores within crystalline chiral metal-organic framework (CMOF) films. This approach harnesses the shaping influence of a polystyrene nanosphere template and the crystallization induced by the liquid dielectric barrier discharge plasma. The resultant highly ordered macro-microporous structures improve mass diffusion and access to chiral active sites in the hierarchical CMOF films. Coupled with their inherent chirality, strong fluorescence emission, high crystallinity, and exceptional stability, these attributes endow these CMOF films with enhanced sensing capabilities for chiral molecules. Particularly, the macro-microporous structure facilitates efficient protein recognition, overcoming a significant challenge encountered by MOFs due to protein dimensions surpassing MOF pore sizes. These films exhibit increased enantioselectivity, better limits of detection, and wider linear ranges compared with purely microporous CMOF films. This study thus provides a powerful synthetic approach for hierarchical CMOF films, addressing the limitations of traditional thin film sensors and opening an avenue for efficient chiral sensing of large biomacromolecules.

Switching from Molecules to Functional Materials: Breakthroughs in Photochromism With MOFs

Photochromic materials with properties that can be dynamically tailored as a function of external stimuli are a rapidly expanding field driven by applications in areas ranging from molecular computing, nanotechnology, or photopharmacology to programable heterogeneous catalysis. Challenges arise, however, when translating the rapid, solution-like response of stimuli-responsive moieties to solid-state materials due to the intermolecular interactions imposed through close molecular packing in bulk solids. As a result, the integration of photochromic compounds into synthetically programable porous matrices, such as metal-organic frameworks (MOFs), has come to the forefront as an emerging strategy for photochromic material development. This review highlights how the core principles of reticular chemistry (on the example of MOFs) play a critical role in the photochromic material performance, surpassing the limitations previously observed in solution or solid state. The symbiotic relationship between photoresponsive compounds and porous frameworks with a focus on how reticular synthesis creates avenues toward tailorable photoisomerization kinetics, directional energy and charge transfer, switchable gas sorption, and synergistic chromophore communication is discussed. This review not only focuses on the recent cutting-edge advancements in photochromic material development, but also highlights novel, vital-to-pursue pathways for multifaceted functional materials in the realms of energy, technology, and biomedicine.

Light-Up Fluorescence and Circularly Polarized Luminescence in Achiral Interlocked Framework via Adaptive Lone Pair-π Interaction Confinement

Interactions between lone pairs and aromatic π systems are significant across biology and self-assembled materials. Herein, employing an achiral confinement metal-organic framework (MOF) encapsulates guest molecules, it is successfully realized that lone pair (lp)-π interaction induces fluorescence "turn-on" and circularly polarized luminescence for the first time. The MOFs synthesized based on naphthalenediimide show nearly non-emissive, which can be light-up by introducing acetone or ester guests containing lone pairs-π interaction. Furthermore, the introduction of a series of lp-rich chiral esters induces supramolecular chirality as well as circularly polarized luminescence in achiral MOFs, while also observing chiral adaptability. This work first demonstrates the luminescence and chiral induction via lone pair electrons-π interactions, presenting a fresh paradigm for the advancement of chiroptical materials.

Multiple Chirality Switching of a Dye-Grafted Helical Polymer Film Driven by Acid & Base

A stimuli-responsive multiple chirality switching material, which can regulate opposed chiral absorption characteristics, has great application value in the fields of optical modulation, information storage and encryption, etc. However, due to the rareness of effective functional systems and the complexity of material structures, developing this type of material remains an insurmountable challenge. Herein, a smart polymer film with multiple chirality inversion properties was fabricated efficiently based on a newly-designed acid & base-sensitive dye-grafted helical polymer. Benefited from the cooperative effects of various weak interactions (hydrogen bonds, electrostatic interaction, etc.) under the aggregated state, this polymer film exhibited a promising acid & base-driven multiple chirality inversion property containing record switchable chiral states (up to five while the solution showed three-state switching) and good reversibility. The creative exploration of such a multiple chirality switching material can not only promote the application progress of current chiroptical regulation technology, but also provide a significant guidance for the design and synthesis of future smart chiroptical switching materials and devices.

Single-Molecule White Circularly Polarized Photoluminescence and Electroluminescence from Dual-Emission Enantiomers

The strategy of integrating conformational isomerization donors and chiral acceptors in a single molecule was proposed to construct white circularly polarized luminescence (WCPL) materials in this work. Consequently, a pair of dual-emission enantiomers, namely (R/S)-DO-PTZ, were designed and synthesized, which displayed white emission with blue and yellow dual-emission bands in solution and solid films with Commission Internationale de l'Eclairage (CIE) coordinates of (0.30, 0.33) and (0.33, 0.35), respectively. Meanwhile, (R/S)-DO-PTZ exhibited a high PLQY of up to 67 % in doped films and clear mirror-image WCPL signals with a |glum| value of 3.0×10-3. Moreover, white circularly polarized electroluminescence (WCPEL) based on organic light-emitting diodes (OLEDs) with (R/S)-DO-PTZ as emitters were also achieved with CIE coordinates of (0.32, 0.37) and EQEmax of 4.7 %, representing the state-of-the-art level of white OLEDs based on single-molecule purely organic emitters. By optimizing the device structure, warm WCPEL devices were further obtained with a |gEL| value of 2.8×10-3, CIE coordinates of (0.37, 0.48) and EQEmax of up to 15.6 %. To our knowledge, this is the first report of CP-WOLEDs based on single-molecule purely organic emitters.

Handedness-Inverted and Stimuli-Responsive Circularly Polarized Luminescent Nano/Micromaterials Through Pathway-Dependent Chiral Supramolecular Polymorphism

The precise manipulation of supramolecular polymorphs has been widely applied to control the morphologies and functions of self-assemblies, but is rarely utilized for the fabrication of circularly polarized luminescence (CPL) materials with tailored properties. Here, this work reports that an amphiphilic naphthalene-histidine compound (NIHis) readily self-assembled into distinct chiral nanostructures through pathway-dependent supramolecular polymorphism, which shows opposite and multistimuli responsive CPL signals. Specifically, NIHis display assembly-induced CPL from the polymorphic keto tautomer, which become predominant during enol-keto tautomerization shifting controlled by a bulk solvent effect. Interestingly, chiral polymorphs of nanofiber and microbelt with inverted CPL signals can be prepared from the same NIHis monomer in exactly the same solvent compositions and concentrations by only changing the temperature. The tunable CPL performance of the solid microbelts is realized under multi external physical or chemical stimuli including grinding, acid fuming, and heating. In particular, an emission color and CPL on-off switch based on the microbelt polymorph by reversible heating-cooling protocol is developed. This work brings a new approach for developing smart CPL materials via supramolecular polymorphism engineering.

Photon Upconversion Cooperates with Downshifting in Chiral Systems: Modulation, Amplification, and Applications of Circularly Polarized Luminescence

Circularly polarized luminescence (CPL)-active materials are increasingly recognized for their potential applications such as 3D imaging, data storage, and optoelectronic devices. Typically, CPL materials have required high-energy (HE) photons for excitation to emit low-energy (LE) circularly polarized light, a process known as downshifting CPL (DSCPL). However, the emergence of upconverted CPL (UCCPL), where the absorption of multi LE photons results in the emission of a single HE photon with circular polarization, has recently attracted considerable attention. This minireview highlights the intricate relationship between upconversion and CPL phenomena. During upconversion, the dissymmetry factor (glum) value can be improved in certain systems. Additionally, the integration of both LE and HE photons in upconversion-downshifting-synergistic systems offers avenues for dual-excitation or dual-emission CPL functionalities. More in detail, the emerging UCCPL based on various photon upconversion mechanisms and their synergy with DSCPL are introduced. Additionally, several examples that demonstrate the applications of UCCPL are presented to highlight the future opportunities.

Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence

Delayed luminescence (DF), including phosphorescence and thermally activated delayed fluorescence (TADF), and circularly polarized luminescence (CPL) exhibit common and broad application prospects in optoelectronic displays, biological imaging, and encryption. Thus, the combination of delayed luminescence and circularly polarized luminescence is attracting increasing attention. The encapsulation of guest emitters in various host matrices to form host-guest systems has been demonstrated to be an appealing strategy to further enhance and/or modulate their delayed luminescence and circularly polarized luminescence. Compared with conventional liquid crystals, polymers, and supramolecular matrices, porous crystalline frameworks (PCFs) including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), zeolites and hydrogen-bonded organic frameworks (HOFs) can not only overcome shortcomings such as flexibility and disorder but also achieve the ordered encapsulation of guests and long-term stability of chiral structures, providing new promising host platforms for the development of DF and CPL. In this review, we provide a comprehensive and critical summary of the recent progress in host-guest photochemistry via the encapsulation engineering of guest emitters in PCFs, particularly focusing on delayed luminescence and circularly polarized luminescence. Initially, the general principle of phosphorescence, TADF and CPL, the combination of DF and CPL, and energy transfer processes between host and guests are introduced. Subsequently, we comprehensively discuss the critical factors affecting the encapsulation engineering of guest emitters in PCFs, such as pore structures, the confinement effect, charge and energy transfer between the host and guest, conformational dynamics, and aggregation model of guest emitters. Thereafter, we summarize the effective methods for the preparation of host-guest systems, especially single-crystal-to-single-crystal (SC-SC) transformation and epitaxial growth, which are distinct from conventional methods based on amorphous materials. Then, the recent advancements in host-guest systems based on PCFs for delayed luminescence and circularly polarized luminescence are highlighted. Finally, we present our personal insights into the challenges and future opportunities in this promising field.

Synthesis Strategies, Preparation Methods, and Applications of Chiral Metal-Organic Frameworks

Chiral Metal-Organic Frameworks (CMOFs) is a kind of material with great application value in recent years. Formed by the coordination of metal ions or metal clusters with organic ligands. It has ordered and adjustable pores, multi-dimensional network structure, large specific surface area and excellent adsorption properties. This material structure combines the properties of metal-organic frameworks (MOFs) with the chiral properties of chiral molecules. It has great advantages in catalysis, adsorption, separation and other fields. Therefore, it has a wide range of applications in chemistry, biology, medicine and materials science. In this paper, various synthesis strategies and preparation methods of chiral metal-organic frameworks are reviewed from different perspectives, and the advantages of each method are analyzed. In addition, the applications of chiral metal-organic framework materials in enantiomer recognition and separation, circular polarization luminescence and asymmetric catalysis are systematically summarized, and the corresponding mechanisms are discussed. Finally, the challenges and prospects of the development of chiral metal-organic frame materials are analyzed in detail.

Obtaining giant Rashba-Dresselhaus spin splitting in two-dimensional chiral metal-organic frameworks

Two-dimensional (2D) nonmagnetic semiconductors with large Rashba-Dresselhaus (R-D) spin splitting at valence or conduction bands are attractive for magnetic-field-free spintronic applications. However, so far, the number of 2D R-D inorganic semiconductors has been quite limited, and the factors that determine R-D spin splitting as well as rational design of giant spin splitting, remain unclear. For this purpose, by exploiting 2D chiral metal-organic frameworks (CMOFs) as a platform, we theoretically develop a three-step screening method to obtain a series of candidate 2D R-D semiconductors with valence band spin splitting up to 97.2 meV and corresponding R-D coupling constants up to 1.37 eV Å. Interestingly, the valence band spin texture is reversible by flipping the chirality of CMOFs. Furthermore, five keys for obtaining giant R-D spin splitting in 2D CMOFs are successfully identified: (i) chirality, (ii) large spin-orbit coupling, (iii) narrow band gap, (iv) valence and conduction bands having the same symmetry at the Γ point, and (v) strong ligand field.

Photoswitching the fluorescence of nanoparticles for advanced optical applications

The dynamic optical response properties and the distinct features of nanomaterials make photoswitchable fluorescent nanoparticles (PF NPs) attractive candidates for advanced optical applications. Over the past few decades, the design of PF NPs by coupling photochromic and fluorescent motifs at the nanoscale has been actively pursued, and substantial efforts have been made to exploit their potential applications. In this perspective, we critically summarize various design principles for fabricating these PF NPs. Then, we discuss their distinct optical properties from different aspects by highlighting the capability of NPs in fabricating new, robust photoswitch systems. Afterwards, we introduce the pivotal role of PF NPs in advanced optical applications, including sensing, anti-counterfeiting and imaging. Finally, current challenges and future development of PF NPs are briefly discussed.

Enhancing Electrochemical Signal for Efficient Chiral Recognition by Encapsulating C60 Fullerene into Chiral Lanthanum-Based MOFs

Chiral metal-organic frameworks (MOFs) have attracted much attention due to their highly tunable regular microporous structures. However, chiral electrochemical recognition based on chiral MOFs is often limited by poor charge separation and slow charge transfer kinetics. In this case, C60 can be encapsulated into the cavity of [La(BTB)]n by virtue of host-guest interactions through π-π stacking to synthesize the chiral composite C60@[La(BTB)]n and amplify electrochemically controlled enantioselective interactions with the target enantiomers. A large electrostatic potential difference is generated in chiral C60@[La(BTB)]n due to the host-guest interaction and the inhomogeneity of the charge distribution, leading to the generation of a strong built-in electric field and thus an overall enhancement of the conductivity of the chiral material. Their enantioselective detection of tryptophan enantiomers was demonstrated by electrochemical measurement. The results showed that chiral MOF materials can be used for enantiomeric recognition. It is worth noting that this new material derived from the concept of host-guest interaction to enhance charge separation opens up unprecedented possibilities for future enantioselective recognition and separation.

Pore engineering of micro/mesoporous nanomaterials for encapsulation, controlled release and variegated applications of essential oils

Essential oils have become increasingly popular in fields of medical, food and agriculture, owing to their strongly antimicrobial, anti-inflammation and antioxidant effects, greatly meeting demand from consumers for healthy and safe natural products. However, the easy volatility and/or chemical instability of active ingredients of essential oils (EAIs) can result in the loss of activity before realizing their functions, which have greatly hindered the widely applications of EAIs. As an emerging trend, micro/mesoporous nanomaterials (MNs) have drawn great attention for encapsulation and controlled release of EAIs, owing to their tunable pore structural characteristics. In this review, we briefly discuss the recent advances of MNs that widely used in the controlled release of EAIs, including zeolites, metal-organic frameworks (MOFs), mesoporous silica nanomaterials (MSNs), and provide a comprehensive summary focusing on the pore engineering strategies of MNs that affect their controlled-release or triggered-release for EAIs, including tailorable pore structure properties (e.g., pore size, pore surface area, pore volume, pore geometry, and framework compositions) and surface properties (surface modification and surface functionalization). Finally, the variegated applications and potential challenges are also given for MNs based delivery strategies for EAIs in the fields of healthcare, food and agriculture. These will provide considerable instructions for the rational design of MNs for controlled release of EAIs.

Metal Clusters Confined in Chiral Zeolitic Imidazolate Framework for Circularly Polarized-Luminescence Inks

Chiroptical activities arising in nanoclusters (NCs) are emerging as one of the most dynamic areas of modern science. However, devising an overarching strategy that is capable of concurrently enhancing the photoluminescence (PL) and circularly polarized luminescence (CPL) of metal NCs remains a formidable challenge. Herein, gold and silver nanoclusters (AuNCs, AgNCs) are endowed with CPL, for the first time, through a universal host-guest approach─centered around perturbing a chiral microenvironment within chiral hosts, simultaneously enhancing emissions. Remarkably, the photoluminescence quantum yield (PLQY) of AuNCs has undergone an increase of over 200 times upon confinement, escalating from 0.05% to 12%, and demonstrates a CPL response. Moreover, a three-dimensional (3D) model termed "NCs@CMOF" featuring CPL activity is created using metal cluster-based assembly inks through the process of 3D printing. This work introduces a potentially straightforward and versatile approach for achieving both PL enhancement and CPL activities in metal clusters.

Full-Color Circularly Polarized Luminescence of Supramolecular Polymers with Handedness Inversion Regulated by Anion and Temperature

Constructing full-color circularly polarized luminescence (CPL) materials with switchable handedness in the solid state is an appealing yet considerably challenging task, especially for supramolecular polymer films assembled from homochiral monomers. Herein, supramolecular polymers with full-color CPL and inverted handedness are realized through the coassembly of a homochiral cholesterol derivative (PVPCC), metal ions (Zn2+), and achiral fluorescent dyes. The obtained coassembled systems show anion-directed supramolecular chirality inversion by exchanging the anions of NO3-, ClO4-, BF4-, and Cl-. For instance, the negative CD and right-handed CPL are detected in the PVPCC/Zn(NO3)2 aggregates, which convert into positive CD and left-handed CPL after introducing Cl-, corresponding to the transformation from nanorods to nanofibers. Furthermore, the tunable CPL color and handedness inversion of the coassembly system of PVPCC/Zn(NO3)2 and achiral fluorescent dyes can be established by alternately changing the assembling temperature of 298 and 273 K. Importantly, the full-color CPL polymeric materials are then constructed by doping the PVPCC/Zn(NO3)2/dyes complexes into poly(methyl methacrylate) (PMMA) film, which maintains the handedness inversion and shows the enhanced CPL performance. The work not only deepens the understanding of chirality inversion in supramolecular chemistry but also helps to construct full-color CPL materials with switchable handedness from homochiral building blocks in materials science.

A Single-Enantiomer Emitter Enabled Superstructural Helix Inversion for Upconverting and Downshifting Luminescence with Bidirectional Circular Polarization

The helical twisting tendency of liquid crystals (LCs) is generally governed by the inherent configuration of the chiral emitter. Here, we introduce the multistage inversion of supramolecular chirality as well as circularly polarized luminescence (CPL) by manipulating the ratio of single enantiomeric emitters (R-PCP) to LC monomers (5CB). Increasing the content of R-PCP from 1 wt % to 3 wt % inverted the helix of LCs from left-handed to right-handed, accompanying a CPL sign changed from positive to negative. The biaxiality of chiral emitters, as well as the steric effect of chiral-chiral and chiral-achiral interaction, were identified as the reasons for helical sense inversion. Due to the strong helical twisting power, 4 wt % R-PCP drove the photonic band gap (PBG) of chiral LCs to match up with their emission range, leading to an inversion of the CPL again with a high dissymmetry factor (≈1.2). Directly adjusting the PBG using chiral emitters is seldom achieved in cholesteric LCs. On this basis, an achiral sensitizer PtTPBP was assembled into the helical superstructure. The generation of triplet-triplet annihilation-induced upconverted CPL from R-PCP and the downshifting CPL from PtTPBP with opposite rotation was achieved in a single chiral LC system by tuning the position of the PBG.

Inducing Circularly Polarized Luminescence by Confined Synthesis of Ultrasmall Chiral Carbon Nanodot Arrays in Pyrene-Based MOF Thin Film

Combining the features of the host-guest system and chirality is an efficient strategy to achieve circularly polarized luminescence (CPL). Herein, well-defined chiral carbon nanodot (chirCND) arrays were confined-synthesized by low-temperature calcination of a chiral amino acid loaded metal-organic framework (MOF) to induce high CPL. An achiral porous pyrene-based MOF NU-1000 thin film as the host template was prepared by a liquid-phase epitaxial layer-by-layer fashion, and chiral amino acids as the carbon sources could be confined in the porous MOF and carbonized to homogeneous and ultrasmall chirCND arrays, resulting in a chirCNDs@NU-1000 thin film (l-CNDsx@NU-1000; x = l-cysteine (cys), l-serine, l-histidine, l-glutamic acid, and l-pyroglutamic acid). The results show the pristine chirCNDs by directly carbonizing chiral amino acids hardly endow them with a CPL property. By contrast, benefiting from the arrayed confinement and coordination interaction between chirCNDs and NU-1000, the chirality transfer on the excited state of chirCNDs@NU-1000 is enabled, leading to strong CPL performance (a high luminescence dissymmetry factor glum of l-CNDscys@NU-1000 thin film reached 1.74 × 10-2). This study of chirCNDs encapsulated in fluorescent MOF thin films provides a strategy for developing uniform chiral carbon nanoarrays and offers chiral host-guest thin-film materials for optical applications.

Chiral Materials: Progress, Applications, and Prospects

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Liquid Crystal Assembly for Ultra-dissymmetric Circularly Polarized Luminescence and Beyond

Circularly polarized luminescence (CPL) is attracting much interest because it can carry extensive optical information. CPL shows left- or right-handedness and can be regarded as part of high-level visual perception to supply an extra dimension of information with regard to regular light. A key to meeting the needs for practical applications is to develop the emerging field of ultra-dissymmetric CPL. Chiral liquid crystal (LC) assemblies─otherwise referred to as cholesteric liquid crystals (CLCs)─are essentially organized helical superstructures with a highly ordered one-dimensional orientation, and distinctly superior to regular helical supramolecules. CLCs can achieve a perfect equilibrium of molecular short-range interaction and long-range orientational order, enabling molecule-scale chirality on a helical pitch and observable scale. LC assembly could be an ideal strategy for amplifying chirality, making it accessible to ultra-dissymmetric CPL. Herein, we focused on some basic but important issues regarding CPL: (i) How can CPL be created from chiral dyes? (ii) Is the chirality of luminescent dyes an essential factor for the generation of CPL? That is, can all chiral dyes emit CPL and vice versa? (iii) How can CPL be transferred within intermolecular systems, and what principles of CPL transmission should be followed? Given these queries and our work, in this Perspective we discuss the generation, transmission, and modulation of CPL with chiral LC assembly, aiming to design and build up novel chiroptical materials. Recent applications of CPL-active LC microstructures in three-dimensional displays, circularly polarized lasers, and asymmetric catalysis are also discussed.

Chiral metal-organic frameworks for photonics

Recently, there has been significant interest in the use of chiral metal-organic frameworks (MOFs) and coordination polymers (CPs) for photonics applications. The promise of these materials lies in the ability to tune their properties through judicious selection of the metal and ligand components. Additionally, the interaction of guest species with the host framework can be exploited to realise new functionalities. In this review, we outline the methods for synthesising chiral MOFs and CPs, then analyse the recent innovations in their use for various optical and photonics applications. We focus on two emerging directions in the field of MOF chemistry - circularly polarised luminescence (CPL) and chiroptical switching - as well as the latest developments in the use of these materials for second-order nonlinear optics (NLO), particularly second-harmonic generation (SHG). The current challenges encountered so far, their possible solutions, and key directions for further research are also outlined. Overall, given the results demonstrated to date, chiral MOFs and CPs show great promise for use in future technologies such as optical communication and computing, optical displays, and all-optical devices.

Stepwise Amplification of Circularly Polarized Luminescence in Chiral Metal Cluster Ensembles

Chiral metal-organic frameworks (MOFs) are usually endowed by chiral linkers and/or guests. The strategy using chiral secondary building units in MOFs for solving the trade-off of circularly polarized luminescence (CPL)-active materials, high photoluminescence quantum yields (PLQYs) and high dissymmetry factors (|g_lum |) has not been demonstrated. This work directionally assembles predesigned chiral silver clusters with ACQ linkers through reticular chemistry. The nanoscale chirality of the cluster transmits through MOF's framework, where the linkers are arranged in a quasi-parallel manner and are efficiently isolated and rigidified. Consequently, this backbone of chiral cluster-based MOFs demonstrates superb CPL, high PLQYs of 50.3%, and |g_lum | of 1.2 × 10^-2 . Crystallographic analyses and DFT calculations show the quasi-parallel arrangement manners of emitting linkers leading to a large angle between the electric and magnetic transition dipole moments, boosting CPL response. As compared, an ion-pair-direct assembly without interactions between linkers induces one-ninth |g_lum | and one-sixth PLQY values, further highlighting the merits of directional arrangement in reticular nets. In addition, a prototype CPL switching fabricated by a chiral framework is controlled through alternating ultraviolet and visible light. This work is expected to inspire the development of reticular chemistry for high-performance chiroptical materials.

Highly Boosting Circularly Polarized Luminescence of Chiral Metal-Imidazolate Frameworks

To develop a simple and general method for improving the circularly polarized luminescence (CPL) performances of materials is of great significance. In this work, two pairs of CPL-active homochiral metal-organic frameworks (MOFs) P/M-Et and P/M-Et(Cd) with eta topology are reported. In comparison to the reported isomorphic Zn-imidazolate MOFs P-Me and M-Me, both luminescence dissymmetry factor (g_lum ) and photoluminescence quantum yields (Φ_PL ) of P-Et and M-Et are largely improved by simply changing the methyl group to an ethyl group of ligands in P-Et and M-Et. Furthermore, the |g_lum | values are significantly amplified up to 0.015 from 0.0057 by introducing the non-luminescent halogenated aromatics, while an enhanced fluorescence efficiency is observed simultaneously (from 27.2% to 47.3%). The figure of merit value is about 40 times larger than that of P-Me and M-Me. Similarly, the CPL performances of P/M-Et(Cd) are improved by about five times after encapsulating fluorobenzene molecules. This work represents a new and simple method for developing CPL-active MOF materials.

Efficient Circularly Polarized Electroluminescence from Achiral Luminescent Materials

Circularly polarized electroluminescence (CP-EL) is generally produced in organic light-emitting diodes (OLEDs) based on special CP luminescent (CPL) materials, while common achiral luminescent materials are rarely considered to be capable of direct producing CP-EL. Herein, near ultraviolet CPL materials with high photoluminescence quantum yields and good CPL dissymmetry factors are developed, which can induce blue to red CPL for various achiral luminescent materials. Strong near ultraviolet CP-EL with the best external quantum efficiencies (η_ext s) of 9.0 % and small efficiency roll-offs are achieved by using them as emitters for CP-OLEDs. By adopting them as hosts or sensitizers, commercially available yellow-orange achiral phosphorescence, thermally activated delayed fluorescence (TADF) and multi-resonance (MR) TADF materials can generate intense CP-EL, with high dissymmetry factors and outstanding η_ext s (30.8 %), demonstrating a simple and universal avenue towards efficient CP-EL.

Induced CPL-Active Materials Based on Chiral Supramolecular Co-Assemblies

Circularly polarized luminescence (CPL) has attracted much interest due to its potential applications on chiral photonic techniques and optoelectronic materials science. As known, dissymmetry factor (g_em ) of CPL is one essential factor for evaluating the features of CPL-active materials. Much attention has focused on how to increase the g_em value, which is one of the most important issues for CPL practical applications. Recently, more and more works have demonstrated that chiral supramolecular could provide the significant strategy to improve the g_em value through the orderly helical superstructure of chiral building blocks. Normally, this kind of chiral supramolecular assembly process can be accompanied by chirality transfer and induction mechanism, which can promote the amplification effect on the induced CPL of achiral dyes. In this review, we fully summarized recent advances on the induced CPL-active materials of chiral supramolecular co-assemblies, their applications in circularly polarized organic light-emitting diodes (CP-OLEDs) and current challenges.

Metal-Photoswitch Friendship: From Photochromic Complexes to Functional Materials

Cooperative metal-photoswitch interfaces comprise an application-driven field which is based on strategic coupling of metal cations and organic photochromic molecules to advance the behavior of both components, resulting in dynamic molecular and material properties controlled through external stimuli. In this Perspective, we highlight the ways in which metal-photoswitch interplay can be utilized as a tool to modulate a system's physicochemical properties and performance in a variety of structural motifs, including discrete molecular complexes or cages, as well as periodic structures such as metal-organic frameworks. This Perspective starts with photochromic molecular complexes as the smallest subunit in which metal-photoswitch interactions can occur, and progresses toward functional materials. In particular, we explore the role of the metal-photoswitch relationship for gaining fundamental knowledge of switchable electronic and magnetic properties, as well as in the design of stimuli-responsive sensors, optically gated memory devices, catalysts, and photodynamic therapeutic agents. The abundance of stimuli-responsive systems in the natural world only foreshadows the creative directions that will uncover the full potential of metal-photoswitch interactions in the coming years.

Limitation of room temperature phosphorescence efficiency in metal organic frameworks due to triplet-triplet annihilation

The effect of triplet-triplet annihilation (TTA) on the room-temperature phosphorescence (RTP) in metal-organic frameworks (MOFs) is studied in benchmark RTP MOFs based on Zn metal centers and isophthalic or terephthalic acid linkers (ZnIPA and ZnTPA). The ratio of RTP to singlet fluorescence is observed to decrease with increasing excitation power density. Explicitly, in ZnIPA the ratio of the RTP to fluorescence is 0.58 at 1.04 mW cm-2, but only 0.42 at (the still modest) 52.6 mW cm-2. The decrease in ratio is due to the reduction of RTP efficiency at higher excitation due to TTA. The density of triplet states increases at higher excitation power densities, allowing triplets to diffuse far enough during their long lifetime to meet another triplet and annihilate. On the other hand, the shorter-lived singlet species can never meet an annihilate. Therefore, the singlet fluorescence scales linearly with excitation power density whereas the RTP scales sub-linearly. Equivalently, the efficiency of fluorescence is unaffected by excitation power density but the efficiency of RTP is significantly reduced at higher excitation power density due to TTA. Interestingly, in time-resolved measurements, the fraction of fast decay increases but the lifetime of long tail of the RTP remains unaffected by excitation power density. This may be due to the confinement of triplets to individual grains, leading decay to be faster until there is only one triplet per grain left. Subsequently, the remaining "lone triplets" decay with the unchanging rate expressed by the long tail. These results increase the understanding of RTP in MOFs by explicitly showing the importance of TTA in determining the (excitation power density dependent) efficiency of RTP. Also, for applications in optical sensing, these results suggest that a method based on long tail lifetime of the RTP is preferable to a ratiometric approach as the former will not be affected by variation in excitation power density whereas the latter will be.

Dimensionality Mediated Highly Repeatable and Fast Transformation of Coordination Polymer Single Crystals for All-Optical Data Processing

A family of coordination polymers (CPs) based on dynamic structural elements are of great fundamental and commercial interest addressing modern problems in controlled molecular separation, catalysis, and even data processing. Herein, the endurance and fast structural dynamics of such materials at ambient conditions are still a fundamental challenge. Here, we report on the design of a series of Cu-based CPs [Cu(bImB)Cl₂] and [Cu(bImB)₂Cl₂] with flexible ligand bImB (1,4-bis(imidazol-1-yl)butane) packed into one- and two-dimensional (1D, 2D) structures demonstrating dimensionality mediated flexibility and reversible structural transformations. Using the laser pulses as a fast source of activation energy, we initiate CP heating followed by anisotropic thermal expansion and 0.2-0.8% volume changes with the record transformation rates from 2220 to 1640 s^-1 for 1D and 2D CPs, respectively. The endurance over 10³ cycles of structural transformations, achieved for the CPs at ambient conditions, allows demonstrating optical fiber integrated all-optical data processing.

A Flexible Circularly Polarized Luminescence Switching Device Based on Proton-Coupled Electron Transfer

Flexible circularly polarized luminescence (CPL) switching devices have been long-awaited due to their promising potential application in wearable optoelectronic devices. However, on account of the few materials and complicated design of manufacturing systems, how to fabricate a flexible electric-field-driven CPL-switching device is still a serious challenge. Herein, a flexible device with multiple optical switching properties (CPL, circular dichroism (CD), fluorescence, color) is designed and prepared efficiently based on proton-coupled electron transfer (PCET) mechanism by optimizing the chiral structure of switching molecule. More importantly, this device can maintain the switching performance even after 300 bending-unbending cycles. It has a remarkable comprehensive performance containing bistable property, low open voltage, and good cycling stability. Then, prototype devices with designed patterns have been fabricated, which opens a new application pattern of CPL-switching materials.

The preparation and properties of circularly polarized luminescent liquid crystal physical gels with self-supporting performance

In recent years, great progress has been made in the preparation methods and performance regulation of host-guest doped CPL liquid crystal materials. However, there still exist some basic problems to be solved, such as complex packaging and unstable CPL properties. With the consideration of the above problems, in this study, we introduced gelators into the host-guest doped CPL liquid crystal materials to prepare CPL liquid crystal physical gels. The gelators can be assembled to form a nanofiber physical gel network, which limits the movement of the liquid crystals and enhances the stability of the CPL properties. Meanwhile, liquid crystal physical gels show self-supporting ability and the gel-sol phase transition temperature can reach 136 °C. The amplification of the g_lum value is achieved by self-assembly of chiral liquid crystals, and the g_lum value can reach -0.31. The phase structure changes with electric field and temperature, and the CPL properties can be regulated by changing the temperature and electric field. With the increasing applied voltage or the temperature, the g_lum value decreases. Therefore, we have successfully prepared a new type of CPL liquid crystal physical gels with self-supporting performance, stimulus response performance and large g_lum values.

Liquid crystal-templated chiral nanomaterials: from chiral plasmonics to circularly polarized luminescence

Chiral nanomaterials with intrinsic chirality or spatial asymmetry at the nanoscale are currently in the limelight of both fundamental research and diverse important technological applications due to their unprecedented physicochemical characteristics such as intense light-matter interactions, enhanced circular dichroism, and strong circularly polarized luminescence. Herein, we provide a comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials. The chiroptical properties of chiral nanomaterials are touched, and their fundamental design principles and bottom-up synthesis strategies are discussed. Different chiral functional nanomaterials based on liquid-crystalline soft templates, including chiral plasmonic nanomaterials and chiral luminescent nanomaterials, are systematically introduced, and their underlying mechanisms, properties, and potential applications are emphasized. This review concludes with a perspective on the emerging applications, challenges, and future opportunities of such fascinating chiral nanomaterials. This review can not only deepen our understanding of the fundamentals of soft-matter chirality, but also shine light on the development of advanced chiral functional nanomaterials toward their versatile applications in optics, biology, catalysis, electronics, and beyond.