Modulating Photo- and Electroluminescence in a Stimuli-Responsive π-Conjugated Donor-Acceptor Molecular System

Luminescent Platinum(II) Complexes with Stimuli-Responsive Flexible Lewis Pair Ligands: Spectroscopic and Computational Studies

A series of new luminescent bimetallic platinum(II) complexes with stimuli-responsive flexible Lewis pair (FlexLP) ligands are described. The FlexLP ligands consist of a dimesitylboron Lewis acid and diphenylphosphine oxide Lewis base which are in equilibrium between the unbound open form and the Lewis adduct, controlled by the hydrogen bond donating strength of the solvent. Spectroscopic techniques and density functional theory (DFT) calculations were used to interpret the photophysics of the platinum(II) complexes. All complexes exhibit tunable absorption in the region of 300-500 nm and green to orange photoluminescence, depending on the ratio of weak (THF) to strong (MeOH) hydrogen bond donating solvent employed. Spectroscopic and computational data shows that phosphine and peripheral acetylide ligands on the platinum(II) centers have limited influence on the emission energy, indicating the emission originates from the FlexLP-dominated fluorescence. Using time-resolved transient absorption spectroscopy it is shown that the complexes undergo intersystem crossing (ISC) to the triplet excited state upon photoexcitation, and the ISC efficiency is affected by the peripheral acetylide ligands. The triplet excited state lifetime can also be manipulated by the state of the FlexLP ligand, with the closed form complexes having longer lifetimes than the open form complexes.

The Solid-State Multi-Color Fluorescence Switching from a [2.2]Paracyclophane-Based Triarylborane

The fluorophores, the fluorescence of which can be switched between multi bright colors in the solid state, show promising applications not only in the sophisticated multicolor display but also in the advanced encryption and anti-counterfeiting systems. However, it is very challenging to obtain such fluorophores. Herein, we disclose such an example, g-BPhANMe2-Cp, which contains an electron-donating dimethylamino (NMe2) and an electron-accepting [(2-dimesitylboryl)phenyl]acetyl at the pseudo-gem position of [2.2]paracyclophane skeleton. This molecule can display tricolor mechanochromic luminescence (MCL) due to the different responses of the mechanically ground amorphous state to heating and solvent-fuming. Owing to the absence of intermolecular π-π interactions in the solid state, the fluorescence efficiency is very high irrespective of its morphological state (ΦF=0.60-0.87). Moreover, this molecule also displays reversible acidochromic luminescence (ACL) by protonation and deprotonation of NMe2 with trifluoroacetic acid (TFA) and triethylamine (TEA), respectively. The protonated sample fluoresces (ΦF=0.31) at much shorter wavelength due to the interruption of intramolecular charge transfer process. Therefore, with the combination of tricolor MCL and ACL properties, the solid-state emission of g-BPhANMe2-Cp can be switched among four bright fluorescence colors of yellow, green, cyan and blue via treatment with appropriate stimulus.

Recent advances in tunable solid-state emission based on α-cyanodiarylethenes: from molecular packing regulation to functional development

The design and development of organic solid-state luminescent materials stand as crucial pillars within the realm of contemporary photofunctional materials. Overcoming challenges such as concentration quenching and achieving tailored luminescent properties necessitates a judicious approach to molecular structure design and the strategic utilization of diverse stimuli to modulate molecular packing patterns. Among the myriad candidates, α-cyanodiarylethenes (CAEs) emerge with distinctive solid-state luminescent attributes, capable of forming self-assembled packing structures with varying degrees of π-π stacking. This characteristic endows them with potential in the field of intelligent molecular responsive materials and optoelectronic devices. This tutorial review embarks on an exploration of design strategies geared towards attaining tunable solid-state emission through customized packing of CAEs. It explores the utilization of stimuli responses, including such as mechanical forces, light irradiation, solvent interactions, thermal influences, as well as the utilization of co-assembly methodologies. The overarching aim of this review is to provide a widely applicable platform fostering the flourishing development of modern organic photofunctional materials through integrating principles of molecular engineering, organic optoelectronics, and materials science.

Full-color, time-valve controllable and Janus-type long-persistent luminescence from all-inorganic halide perovskites

Long persistent luminescence (LPL) has gained considerable attention for the applications in decoration, emergency signage, information encryption and biomedicine. However, recently developed LPL materials - encompassing inorganics, organics and inorganic-organic hybrids - often display monochromatic afterglow with limited functionality. Furthermore, triplet exciton-based phosphors are prone to thermal quenching, significantly restricting their high emission efficiency. Here, we show a straightforward wet-chemistry approach for fabricating multimode LPL materials by introducing both anion (Br-) and cation (Sn2+) doping into hexagonal CsCdCl3 all-inorganic perovskites. This process involves establishing new trapping centers from [CdCl6-nBrn]4- and/or [Sn2-nCdnCl9]5- linker units, disrupting the local symmetry in the host framework. These halide perovskites demonstrate afterglow duration time ( > 2,000 s), nearly full-color coverage, high photoluminescence quantum yield ( ~ 84.47%), and the anti-thermal quenching temperature up to 377 K. Particularly, CsCdCl3:x%Br display temperature-dependent LPL and time-valve controllable time-dependent luminescence, while CsCdCl3:x%Sn exhibit forward and reverse excitation-dependent Janus-type luminescence. Combining both experimental and computational studies, this finding not only introduces a local-symmetry breaking strategy for simultaneously enhancing afterglow lifetime and efficiency, but also provides new insights into the multimode LPL materials with dynamic tunability for applications in luminescence, photonics, high-security anti-counterfeiting and information storage.

Multicolor Photochemical Printing Inside Polymer Matrices for Advanced Photonic Anticounterfeiting

Conventional security inks, generally directly printed on the data page surface, are vulnerable to counterfeiters, thereby raising the risk of chemical structural deciphering. In fact, polymer film-based data pages with customized patterns embedded within polymer matrix, rather than printed on the surface, emerge as a promising solution. Therefore, the key lies in developing fluorophores offering light dose-controlled fluorescent color inside polymer matrices. Though conventional fluorophores often suffer from photobleaching and uncontrolled photoreactions, disqualifying them for this purpose. Herein a diphenanthridinylfumaronitrile-based phototransformers (trans-D5) that undergoes photoisomerization and subsequent photocyclization during photopolymerization of the precursor, successively producing cis- and cyclo-D5 with stepwise redshifted solid-state emissions is developed. The resulting cyclo-D5 exhibits up to 172 nm emission redshift in rigidifying polymer matrices, while trans-D5 experiences a slightly blueshifted emission (≈28 nm), cis-D5 undergoes a modest redshift (≈14 nm). The markedly different rigidochromic behaviors of three D5 molecules within polymer matrices enable multicolor photochemical printing with a broad hue ranging from 38 to 10 via an anticlockwise direction in Munsell color space, yielding indecipherable fluorescent patterns in polymer films. This work provides a new method for document protection and implements advanced security features that are unattainable with conventional inks.

Stimuli-fluorochromic smart organic materials

Smart materials based on stimuli-fluorochromic π-conjugated solids (SFCSs) have aroused significant interest due to their versatile and exciting properties, leading to advanced applications. In this review, we highlight the recent developments in SFCS-based smart materials, expanding beyond organometallic compounds and light-responsive organic luminescent materials, with a discussion on the design strategies, exciting properties and stimuli-fluorochromic mechanisms along with their potential applications in the exciting fields of encryption, sensors, data storage, display, green printing, etc. The review comprehensively covers single-component and multi-component SFCSs as well as their stimuli-fluorochromic behaviors under external stimuli. We also provide insights into current achievements, limitations, and major challenges as well as future opportunities, aiming to inspire further investigation in this field in the near future. We expect this review to inspire more innovative research on SFCSs and their advanced applications so as to promote further development of smart materials and devices.

One stimulus-induced two-step photophysical response with high contrast and tunable switching time for dynamic displaying

One stimulus-induced two-step photophysical response, especially with tunable switching time, is a great challenge for organic chromophores. Herein, a polymorphic material 2,7-DCF could undergo in situ two sequential dual-channel responses upon dichloromethane fuming. Both the appearance color and the fluorescence change from red to yellow to deep red with high contrast. The first step corresponds to a fast amorphous-to-crystalline transformation, while the second is a slow solid-state cocrystallization process. Based on single crystal structures and theoretical calculations, such distinct color changes are mainly attributed to conformation twisting and the electron coupling with incorporated solvent molecule through C-H⋅⋅⋅O interaction. Importantly, the second slow photophysical response could be drastically sped up by seeding strategy, or be totally inhibited. Such characteristics pave a way for the potential applications in dynamic anti-counterfeiting and data encryption. Based on the two-step transformation, polymorph 2,7-DCF-a could achieve a successive four-level response to external stimuli. In contrast, polymorph 2,7-DCF-d exhibits a stepwise hypsochromic fluorescence shift over 100 nm. This study would significantly promote the development of stimuli-sensitive systems from "one stimulus, one-step response" to "one stimulus, two or multi-step response".

Molecular and Aggregate Synergistic Engineering of Aggregation-Induced Emission Luminogens to Manipulate Optical/Electronic Properties for Efficient and Diversified Functions

The optical/electronic properties of organic luminescent materials can be regulated by molecular structure modification, which not only requires sophisticated and time-consuming synthesis but also is unable to accurately afford the optical properties of materials in the aggregate state. Herein, a facile strategy of molecular and aggregate synergistic engineering is proposed to manipulate the optical/electronic properties of a luminogen, ACIK, in the solid state for efficient and diversified functions. ACIK is facilely synthesized and exhibits three polymorphic states (ACIK-Y, ACIK-R, and ACIK-N) with a large emission difference of 102 nm from yellow to near-infrared (NIR). Their structure-property relationships were investigated by crystallographic analyses and computational studies. ACIK-Y, with the most twisted structure, exhibits an intriguing color-tuned fluorescence between yellow and NIR in the solid state in response to multiple stimuli. Shuttle-like ACIK-R microcrystals exhibit an optical waveguide property with a low optical loss coefficient of 19 dB mm^-1. ACIK dots display bright NIR-I emission, large Stokes shift, and strong NIR-II two-photon absorption. ACIK dots show specific lipid droplets-targeting capability and can be successfully applied for two-photon fluorescence imaging of mouse brain vasculature with deep penetration and high spatial resolution. This study will inspire more insights in developing advanced optical/electronic materials based on a single chromophore for practical applications.

Pillararene-Based Supramolecular Polymers for Cancer Therapy

Supramolecular polymers have attracted considerable interest due to their intriguing features and functions. The dynamic reversibility of noncovalent interactions endows supramolecular polymers with tunable physicochemical properties, self-healing, and externally stimulated responses. Among them, pillararene-based supramolecular polymers show great potential for biomedical applications due to their fascinating host-guest interactions and easy modification. Herein, we summarize the state of the art of pillararene-based supramolecular polymers for cancer therapy and illustrate its developmental trend and future perspective.

Control of Fluorescence of Organic Dyes in the Solid-State by Supramolecular Interactions

Fluorescent organic dyes play an essential role in the creation of new "smart" materials. Fragments and functional groups capable of free rotation around single bonds can significantly change the fluorescent organic dye's electronic structure under analyte effects, phase state transitions, or changes in temperature, pressure, and media polarity. Dependencies between steric and electronic structures become highly important in transition from a solution to a solid-state. Such transitions are accompanied by a significant increase in the dye molecular structure's rigidity due to supramolecular associates' formation such as H-bonding, π···π and dipole-dipole interactions. Among those supramolecular effects, H-bonding interactions, first of all, lead to significant molecular packing changes between loose or rigid structures, thus affecting the fluorescent dye's electronic states' energy and configuration, its fluorescent signal's position and intensity. All the functional groups and heteroatoms that are met in the organic dyes seem to be involved in the control of fluorescence via H-bonding: C-H···N, C-H···π, S = O···H-C, P = O···H, C-H···O, NH···N, C - H···C, C - H···Se, N-H···O, C - H···F, C-F···H. Effects of molecular packing of fluorescent organic dyes are successfully used in developing mechano-, piezo-, thermo- fluorochromes materials for their applications in the optical recording of information, sensors, security items, memory elements, organic light-emitting diodes (OLEDs) technologies.

Molecular Engineering of Push-Pull Diphenylsulfone Derivatives towards Aggregation-Induced Narrowband Deep Blue Thermally Activated Delayed Fluorescence (TADF) Emitters

Narrowband deep blue thermally activated delayed fluorescent (TADF) materials have attracted significant attention. Herein, four asymmetrical structured TADF emitters based on diphenylsulfone (DPS) acceptor and 9,9-dimethyl-9,10-dihydroacridine (DMAC) donor with progressive performances were developed. The tert-butyloxy auxiliary electron-donor was adopted to restrict the intramolecular rotations and provide efficient steric hindrance. Regioisomerization by altering the substitution position of DMAC on DPS unit further enhanced the intra- and inter-molecular interactions. The accompanying effects yielded increased energy level, minimized reorganization energy, and inhibited non-radiative transitions in the crystals of tBuO-SOmAD, which achieved narrowband deep-blue emission peaking at 424 nm (FWHM=64 nm, Φ_F =33.6 %) through aggregation-induced, blue-shifted emission (AIBSE). In addition, deep-blue organic light emitting diodes (OLEDs) based on tBuO-SOmAD realized the electroluminescence (EL) spectrum peaking located at 435 nm and CIE coordination of (0.12, 0.09).

A simple molecular design towards the conversion of a MCL backbone to a multifunctional emitter exhibiting polymorphism, AIE, TADF and MCL

Compared with the large number of single-function materials such as aggregation-induced emission (AIE), mechanochromic luminescence (MCL), or thermally activated delayed fluorescence (TADF) emitters, multifunctional emitting materials offer more opportunities in practical applications. In this report, we provide a simple molecular design strategy towards the conversion of a MCL building block to a multifunctional emitter. Through altering the substituent sites and increasing the number of electron donors and steric hindrance on a normal MCL backbone benzo[d,e]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one, a novel multifunctional material 10,11-bis-(4-diphenylamino-phenyl)-benzo[d,e]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (10,11-2TPA-BBI) is designed and synthesized. 10,11-2TPA-BBI exhibits simultaneous polymorphism, AIE, MCL and TADF properties. It can form four different aggregate species: yellow solid (YS) and orange solid (OS), orange flake-shaped crystal (OC), and red prism-like crystal (RC). Among them, because of the small energy gaps (ΔE_STs < 0.3 eV) between the singlet and triplet excited states, OS, OC and RC exhibit TADF properties, while YS show normal fluorescence characteristics with a large ΔE_ST of 0.33 eV. OS can be reversibly transformed into YS upon external stimuli, which can be attributed to the emission switch between local excited state and charge transfer state. Crystallographic study indicates that the bulky structure and weak intermolecular interactions account for polymorphism and AIE properties. This work will provide a simple molecular design strategy for multifunctional materials.

Excitation-Wavelength-Dependent Organic Long-Persistent Luminescence Originating from Excited-State Long-Range Proton Transfer

Stimuli-responsive functional luminescent materials with tunable color and long-persistent emission have emerged as a powerful tool in information encryption, anticounterfeiting, and bioelectronics. Herein, we prove a novel strategy for manipulating the proton transfer pathways in the salicylaldehyde derivative EQCN solutions/powder to produce excitation wavelength-dependent (Ex-De) performances with switchable emissions (blue-sky, green, and orange). The experiments and theoretical results demonstrated that the different luminous colors are originated from enol (E) form (blue-sky), Keto-1 (K1) form (orange) through the excited-state intramolecular proton transfer (ESIPT) process, and Keto-2 (K2) form (green) through the excited-state long-range proton transfer (ESLRPT) process. We leverage synergistic effects between the dopant and matrix (dimethyl terephthalate, DTT) to manipulate the excited-state proton transfer pathway in EQCN@DTT mixture powders to generate Ex-De long-persistent luminescence (Ex-De-LPL), which can be well applied in multilevel information encryption. This strategy not only paves an intriguing way for the construction and preparation of pure organic Ex-De materials but also offers a guideline for developing LPL materials based on ESLRPT processes.

Design of Stimuli-Responsive Phenothiazine Derivatives with Triplet-Related Dual Emission and High-Contrast Mechanochromism Guided by Polymorph Prediction

The development of high-contrast stimulus-responsive materials with excited triplet emission is of great significance for anti-counterfeiting, sensor and memory applications, but remains a challenge. Here, we report a strategy for the rational design of stimulus-responsive phenothiazine derivatives with triplet-related dual emissions and high-contrast mechanochromism guided by Polymorph Prediction. The designed phenothiazine derivatives have the characters of simple structures, a facile synthetic procedure, and a good crystalline nature. We found that the crystals of those derivatives with the potential to form both quasi-axial (ax) and quasi-equatorial (eq) conformations could undergo conformation transition and show significant emission difference (Δλ_em >100 nm) under mechanical force. Meanwhile, all these phenothiazine derivatives exhibit aggregation-induced emission and emit room-temperature phosphorescence or thermally activated delayed fluorescence. The significant luminescent change of these materials under different stimuli gives them promise for applications in encryption and anti-counterfeiting.

Synthesis of Unsymmetrical Diarylfumaronitriles via Tandem Michael Addition and Oxidation under K3Fe(CN)6/O2 System

An efficient formal alkenyl C-H cyanation reaction has been developed for the general synthesis of unsymmetrical diarylfumaronitriles in good to excellent yields. The reaction was achieved through tandem Michael addition and an oxidative process. The merits of this transformation include the use of K₃Fe(CN)₆ as a safe and nontoxic cyanide source, without an external noble metal catalyst, oxygen-involved reactions, easily available raw materials, good functional group tolerance, high stereoselectivity, and potential further application of the products.

Concomitant Photoresponsive Chiroptics and Magnetism in Metal-Organic Frameworks at Room Temperature

Stimulus-responsive metal-organic frameworks (MOFs) can be used for designing smart materials. Herein, we report a family of rationally designed MOFs which exhibit photoresponsive chiroptical and magnetic properties at room temperature. In this design, two specific nonphotochromic ligands are selected to construct enantiomeric MOFs, {Cu₂(L-mal)₂(bpy)₂(H₂O)·3H₂O}_n (1) and {Cu₂(D-mal)₂(bpy)₂(H₂O)·3H₂O}_n (2) (mal = malate, bpy = 4, 4′ − bipyridine), which can alter their color, magnetism, and chiroptics concurrently in response to light. Upon UV or visible light irradiation, long-lived bpy⁻ radicals are generated via photoinduced electron transfer (PET) from oxygen atoms of carboxylates and hydroxyl of malates to bpy ligands, giving rise to a 23.7% increase of magnetic susceptibility at room temperature. The participation of the chromophores (-OH and -COO⁻) bound with the chiral carbon during the electron transfer process results in a small dipolar transition; thus, the Cotton effects of the enantiomers are weakened along with a photoinduced color change. This work demonstrates that the simultaneous responses of chirality, optics, and magnetism can be achieved in a single compound at room temperature and may open up a new pathway for designing chiral stimuli-responsive materials.

Light-emitting analogues based on triphenylamine modified quinoxaline and pyridine[2,3-b]pyrazine exhibiting different mechanochromic luminescence

A series of light-emitting analogues show different mechanochromic luminescence properties with emission color changes of 42 and 10 nm.

Control over Kinetic and Thermodynamically Driven Pathways of Crystallization to Yield Cofacial and Slipped-Stack Dimers in Single Crystals

Control over the molecular packing in the solid state is of utmost importance in regulating the bulk optical properties of organic semiconductors. The electronic coupling between the molecules makes it possible to improve the properties of the bulk materials. This work reports an example of control over the selective formation of polymorphic single crystals of donor-acceptor-type small-molecule compound 25TR by 1) kinetic or 2) thermodynamic course of crystallisation to yield slipped stack (S) and cofacial (C) dimers in the single crystals. The distinct optical characteristics of the C-dimer and S-dimer are summarised. Both forms show significant excitonic interactions in the solid state, and the S-dimeric form has strong yellowish orange fluorescence, whereas the C-dimeric form is non-fluorescent in the crystalline state. DFT calculations and differential scanning calorimetric experiments revealed that the C-dimer polymorph is the thermodynamically stable form with a free energy offset of 0.43 eV in comparison with the S-dimer. Interestingly, the thermodynamically driven non-fluorescent single crystal was found to be convertible to its fluorescent form irreversibly by thermal trigger. The charge-carrier-transport characteristics of these two polymorphs were computed by using the Marcus-Hush formalism. The computations of the charge-carrier-transport behaviour revealed that the S-dimer (25TR_(R) ) is ambipolar, whereas the C-dimer (25TR_(Y) ) is predominantly n-type.

Mechanochromic Delayed Fluorescence Switching in Propeller-Shaped Carbazole-Isophthalonitrile Luminogens with Stimuli-Responsive Intramolecular Charge-Transfer Excited States

Herein, the universal design of high-efficiency stimuli-responsive luminous materials endowed with mechanochromic luminescence (MCL) and thermally activated delayed fluorescence (TADF) functions is reported. The origin of the unique stimuli-triggered TADF switching for a series of carbazole-isophthalonitrile-based donor-acceptor (D-A) luminogens is demonstrated based on systematic photophysical and X-ray analysis, coupled with theoretical calculations. It was revealed that a tiny alteration of the intramolecular D-A twisting in the excited-state structures governed by the solid morphologies is responsible for this dynamic TADF switching behavior. This concept is applicable to the fabrication of bicolor emissive organic light-emitting diodes using a single TADF emitter.

Stimuli-Responsive Aggregation-Induced Delayed Fluorescence Emitters Featuring the Asymmetric D-A Structure with a Novel Diarylketone Acceptor Toward Efficient OLEDs with Negligible Efficiency Roll-Off

Multifunctional luminescent materials with aggregation-induced delayed fluorescence (AIDF) are capable of suppressing concentration-caused emission quenching and exciton annihilation when used as organic light-emitting diode (OLED) emitters. In this contribution, three stimuli-responsive AIDF luminogens, pipd-BZ-PXZ, pipd-BZ-PTZ, and pipd-BZ-DMAC, featuring a D-A asymmetric framework based on a fused N-heterocycle diarylketone acceptor (imid-azo[1,2-a]pyridin-2-yl(phenyl)methanone pipd) are designed and synthesized. Interestingly, pipd-BZ-PTZ forms two different kinds of crystals (G-crystal and O-crystal) with distinct intermolecular interactions between pipd moieties. The G-crystal with a looser packing mode presents significant morphology-dependent stimuli-responsive behavior with a shifted emission wavelength of 56 nm. Generated by a strong intramolecular charge transfer effect, pipd-BZ-PXZ and pipd-BZ-PTZ exhibit orange to red emission in solution and neat films. Both nondoped and doped devices are fabricated for comparison. Nondoped devices present moderate performance with external quantum efficiencies and current efficiency that reach 7.04% and 19.86 cd A^-1, respectively, and the corresponding efficiency roll off at 1000 cd m^-2 is as small as 2.3%, which is among the best records of AIDF-OLEDs with an emission wavelength over 570 nm. Doped devices show better performance with corresponding efficiencies of up to 55.41 cd A^-1 and 15.77%.

Stimuli-Responsive Room-Temperature N-Heteroacene Liquid: In Situ Observation of the Self-Assembling Process and Its Multiple Properties

A novel stimuli-responsive room-temperature photoluminescent liquid 1 based on the N-heteroacene framework is developed and analyzed by several experiments such as differential scanning calorimetry, X-ray diffraction, dynamic viscoelasticity measurement, in situ observation by optical and polarized optical microscopes, UV-vis absorption and fluorescence spectroscopy, and by theoretical methods such as ab initio calculation and molecular dynamics (MD) computer simulation techniques. In contrast to stimuli-responsive solid materials reported previously, liquid 1 in response to HCl vapor as a single stimulus can involve dramatically multiple changes in physical properties such as rheological behavior, morphology, as well as photoluminescence. The present ab initio calculation and microsecond-timescale MD simulations reveal that the complexation of 1 and HCl molecules induces a large dipole moment, leading to the formation of stacking structures because of their dipole-dipole interaction. Upon exposure to HCl vapor, in situ microscopic observation of the stimuli-responsive liquid elucidates a self-assembling process involving the formation of the wrinkle structure in a micrometer scale, indicating disorder-order phase transition. Further exposure of 1 to HCl vapor from seconds to hours has an influence on the macroscopic physical properties such as viscosity, viscoelasticity, and photoluminescent colors. The synergy between the experimental and theoretical investigations opens a new strategy to develop a novel class of stimuli-responsive materials showing multiple changes in physical properties.

Eu2+/Eu3+-Based Smart Duplicate Responsive Stimuli and Time-gated Nanohybrid for Optical Recording and Encryption

With the rapid development of information science, it is urgent that memory devices possessing high security, density, and desirable storage ability should be developed. In this work, a smart duplicate response of stimuli has been developed and a time-gate nanohybrid based on variable valence Eu²⁺/Eu³⁺ coencapsulated has been fabricated and acts as active material in the multilevel and multidimensional memory devices. The luminescence lifetime of Eu³⁺ in this nanohybrid gave a stimuli response due to which the energy level of the coordinated ligand could be modulated. Furthermore, by a simple sintering procedure, Eu³⁺ was partially in situ reduced to Eu²⁺ with a short lifetime in the system. And the in situ reduction ensured both Eu³⁺ and Eu²⁺ ions' uniform distribution in the nanohybrid and simultaneous response upon light excitation of variable valence Eu ions. Interestingly, Eu³⁺ revealed a prolonged lifetime because of the presence of an energy-transfer effect of Eu²⁺ → Eu³⁺. Such a nanohybrid had abundant luminescent properties, including the short lifetime of Eu²⁺, the energy transfer from the Eu²⁺ to Eu³⁺ ions, and the stimuli response of the Eu³⁺ lifetimes when exposed to acidic or basic vapor, thus giving birth to interesting recording and encryption performance in spatial-temporal dimensions. We believe that this research will point out a new direction for the future development of multilevel and multidimensional optical recording and encryption materials.

Mechanochromic fluorescence based on a combination of acceptor and bulky donor moieties: tuning emission color and regulating emission change direction

Mechanochromic fluorescence based on a conventional strategy using a donor–acceptor structure bearing nonplanar three-dimensional donor moieties was studied.