Novel Bisthienylethene Containing Ferrocenyl‐Substituted Naphthalimide: A Photo‐ and Redox Multi‐Addressable Molecular Switch

A new photochromic bisthienylethene system (BTE? NAFc) is reported in which the ferrocene unit (Fc) is incorporated into a naphthalimide chromophore as the central ethene bridging unit. The incorporated Fc unit in the photochromic system of BTE? NAFc has several effects on optical properties, such as fluorescence‐modulation through photoinduced electron transfer (PET), a decrease in the photochromic cyclization quantum yield, and a selective two‐step oxidation process. The ability to drive ring‐opening and ring‐closing reactions with a secondary redox‐modulation provides increased functionality to the photochromic system. Based on these meaningful photo‐ and redox‐modulation properties, five unprecedented multi‐addressable states (BTE? NAFc, BTE? NAFc⁺, c‐BTE? NAFc, c‐BTE? NAFc⁺, and BTE⁺? NAFc⁺) and gated photochromism are successfully obtained within the unimolecular BTE platform, thus providing deeper insight into photochromic systems as multifunctional outputs.     

Photochromic Properties of New Dithienylethene Copolymer

Photochromic molecular switches can be important memory media for optical information processing and storage as long as their thermal stability and photo-fatigue resistance met certain criteria. Among many photochromic materials, heterocyclic diarylethenes have displayed desirable optical switching characteristics. Specifically, bisthienylethene (BTE)-based photochromic switches have demonstrated high sensitivity and rapid response as well as thermal- and photostability^[1,2]. It has been shown that various BTEs can undergo ca.l0^[4] cycles before significant evidence of fatigue^[3]. It is important that molecules with otherwise improved switching characteristics retain this level of fatigue resistance. For example, the improved characteristics include that the absorption of close form of photochromic materials should be shifted to shorter wavelength region due that semiconductor laser shift to short wavelength are developing trend for high density information storage. Also, fatigue may be different in the solid state than in solution. In general, precedent photochromic polymers consisted of photochromic molecules either dispersed in a matrix or covalent grafted onto the polymer main chain.     

Rhodamine Mechanophore Functionalized Mechanochromic Double Network Hydrogels with High Sensitivity to Stress

Mechanochromic hydrogels, a new class of stimuli-responsive soft materials, have potential applications in a number of fields such as damage reporting and stress/strain sensing. We prepared a novel mechanochromic hydrogel using a strategy that has been developed to prepare dual-network(DN) hydrogels. A hydrophobic rhodamine derivative(Rh mechanophore) was covalently incorporated into a first network as a cross-linker. This first network embedded with Rh mechanophore within the DN hydrogel was pre-stretched. This guaranteed that the stress could be transferred extensively to the Rh-crosslinked first network once the hydrogel was under an applied force. Interestingly, we found that the threshold stress required to activate the mechanochromism of the hydrogel was less than 200 kPa, and much less than those in previous reports. Moreover, because of the excellent sensitivity of the hydrogel to stress, the DN hydrogel exhibited reversible freezing-induced mechanochromism. Benefiting from the sensitivity of Rh mechanophore to both p H and force, the DN hydrogel showed p H-regulated mechanochromic behavior. Our experimental results indicate that the preparation strategy we used introduces sensitive mechanochromism into the hydrogel and preserves the advantageous mechanical properties of the DN hydrogel. These results will be beneficial to the design and preparation of mechanochromic hydrogels with high stress sensitivity, and foster their practical applications in a number of fields such as damage reporting and stress/strain sensing.     

Aromaticity‐Controlled Thermal Stability of Photochromic Systems Based on a Six‐Membered Ring as Ethene Bridges: Photochemical and Kinetic Studies

Three photochromic compounds—2‐butyl‐5,6‐bis[5‐(4‐methoxyphenyl)‐2‐methylthiophen‐3‐yl]‐1 H‐benzo[de]isoquinoline‐1,3(2 H)‐dione (BTE‐NA), 4,5‐bis[5‐(4‐methoxyphenyl)‐2‐methylthiophen‐3‐yl]benzo[c][1,2,5]thiadiazole (BTA), and BTTA, which contain naphthalimide, benzothiadiazole, and benzobisthiadiazole as six‐membered ethene bridges with different aromaticities—were systematically studied in solution, sol–gel, and single‐crystal states. They exhibit typical photochromic performance with considerably high cyclization quantum yields. BTE‐NA, BTA, and BTTA form a typical donor–π–acceptor (D –π–A) system with significant intramolecular charge transfer (ICT) between HOMO and LUMO upon excitation, thus realizing the fluorescence modulation by both photochromism and solvatochromism. The three ethene bridges with different degrees of aromaticity can provide a systematic comparison of the thermal stability evolution for their corresponding closed forms (c‐BTE‐NA, c‐BTA, and c‐BTTA). c‐BTE‐NA shows first‐order decay in various solvents from cyclohexane to acetonitrile. c‐BTA only shows first‐order decay in polar solvents such as chloroform, whereas it is stable in nonpolar solvents like toluene. In contrast, the less aromatic property of BTTA gives rise to its unprecedented thermal stability in various solvents even at elevated temperatures in toluene (328 K). Moreover, the small energy barrier between the parallel and antiparallel conformers allows the full conversion from BTTA to c‐BTTA. In well‐ordered crystal states, all three compounds adopt a parallel conformation. Interestingly, BTTA forms a twin crystal of asymmetric nature with interactions between the electron‐rich oxygen atom of the methoxy group and the carbon atom of the electron‐deficient benzobisthiadiazole moiety. This work contributes to the understanding of aromaticity‐controlled thermal stability of photochromic systems based on a six‐membered ring as an ethene bridge, and a broadening of the novel building blocks for photochromic bisthienylethene systems.     

A Tri-state Fluorescent Switch with “Gated” Solid-state Photochromism Induced by an External Force

Mr. Chen Qian, Dr. Zhimin Ma, Mr. Jianwei Liu, Mrs. Xue Zhang, Prof. Shitao Wang and Prof. Zhiyong Ma. In this article, we report a newly designed molecule composed of a dihydroazulene (DHA) group and a phenothiazine (PTZ) moiety, which achieves aggregation-induced emission enhancement (AIEE), mechanochromism and “gated” solid-state photochromism upon stimulation by an external force. Grinding loosens intermolecular interactions in the crystal and causes a red-shift of fluorescence from 570 nm to 600 nm. Meanwhile, the ring-opening reaction of DHA unit is activated by grinding and a remarkable photochromism could be observed from the grinded powder. The reddish emission of the grinded powder peaked at 600 nm weakened gradually and finally became dark, and a new absorption band at 470 nm emerged in the absorption spectra. Time-dependent density functional theory (TD-DFT) calculation results reveal that the intramolecular intramolecular charge-transfer (ICT) process is replaced by a locally excited (LE) emission on the DHA group, which leads to the quenching of fluorescence. Its impressive photochromic property inspired us to a simple but effective way to develop an encryption system which can let the correct information be displayed upon external stimulation.     

Photochromic Benzo[b]phosphole Alkynylgold(I) Complexes with Mechanochromic Property to Serve as Multistimuli‐Responsive Materials

A series of novel benzo[b]phosphole alkynylgold(I) complexes has been demonstrated to display photochromic and mechanochromic properties upon applying the respective stimuli of light and mechanical force. Promising multistimuli‐responsive properties of this series of gold(I) complexes have been successfully achieved through judicious molecular design, which involves incorporation of the photochromic dithienylethene‐containing benzo[b]phosphole into the triphenylamine‐containing arylethynyl ligand that is susceptible to mechanical force‐induced color changes via gold(I) complexation. With excellent thermal irreversibility and robust fatigue resistance of this series of gold(I) complexes, multicolor states controlled by the photochromism and mechanochromism have been realized. Repeatable photochromic and mechanochromic cycles without apparent loss of reactivity have also been observed under ambient conditions. The present work provides important insight and an alternative strategy for the molecular design of multistimuli‐responsive materials, paving the way for further development of the underexplored photoresponsive gold(I) complexes and the multistate photocontrolled system.     

Photo-Switchable Aggregation-Induced Emission of Bisthienylethene-Dipyrimido[2,1-b][1,3]benzothiazole Triad

A bisthienylethene-dipyrimido[2,1-b][1,3]benzothiazole (BTE-2PBT) triad has been designed and synthesized based on our recent discovery of PBTs as atypical propeller-shaped novel AIEgens. The triad not only maintains the photochromic properties of BTE moiety in solution, film, and solid state but also exhibits remarkable AIE properties. Moreover, the fluorescence of BTE-2PBT PMMA film could be modulated with high contrast by alternate UV and visible light irradiation. Photoerasing, rewriting, and non-destructive readout of fluorescent images on BTE-2PBT PMMA film well demonstrate its potential application as optical memory media.     

Unsymmetrical photochromic bithienylethene-bridge tetraphenylethene molecular switches: Synthesis,aggregation-induced emission and information storage

Aggregation-induced emission(AIE) active photochromic molecules have attracted growing attention for their versatile applications.Here we designed and synthesized five newly unsymmetrical photochromic diarylethene(DAE) dyads(BTE1-5) by connecting tetraphenylethene(TPE) and aromatic substituent via bithienylethene(BTE) bridge.The chemical structures of those compounds were identified by ^1H NMR,¹³C NMR and HRMS.The absorption and emission of these dyads were investigated by UV-vis and fluore scence spectroscopy,respectively.The results showed that all those compounds exhibited typically AIE or aggregation-induced emission enhancement(AIEE) characteristic.Particularly,when an aggregationcaused quenching(ACQ) fluorophore(triphenylamine) was grafted to the molecule,connecting with TPE via BTE-bridge,the ACQ phenomenon was dissipated and converted to an AIE luminophore,and those compounds exhibited photochromism upon irradiation with alternative UV and visible light.The solution or solid of those compounds showed distinctly fluorescence switching "ON" or "OFF" observation upon irradiation with alternative UV and visible light.It is interesting that BTE1 could be applied in recording and rewritable information storage,and the cyclization quantum yields could be affected by substituent significantly.     

Multiple Anti‐Counterfeiting Guarantees from a Simple Tetraphenylethylene Derivative – High‐Contrasted and Multi‐State Mechanochromism and Photochromism

Herein the novel tetraphenylethylene (TPE) derivative 1 was designed with an integration of aggregation‐induced emission (AIE), multi‐state mechanochromism and self‐recovery photochromism. The molecule was susceptible to grinding, heating and vapor fuming and showed corresponding transition of its emission colors. The heated powder or single crystal of 1 exhibited reversible photochromism. After a short period of UV irradiation, it showed a bright red color, but recovered to its original white appearance within 1 min. The photochromism is due to the formation of photocyclization intermediates upon UV irradiation, while the eversible mechanochromism is attributed to the weak molecular interactions derived from head‐to‐tail stacking of the molecules. This reversible multi‐state, high‐contrasted and rapid responsive mechanochromic and photochromic property cooperatively provide double enhancement of a multimode guarantee in advanced anti‐counterfeiting.     

Bisthienylethenes Containing a Benzothiadiazole Unit as a Bridge: Photochromic Performance Dependence on Substitution Position

A conveniently synthesized photochromic compound, BTB‐1, containing an unprecedented six‐membered 2,1,3‐benzothiadiazole unit as the center ethene bridge, possesses good photochromic performance, with a high cyclization quantum yield and moderate fatigue resistance in solution or an organogel system. The fluorescence of BTB‐1 can be modulated by solvato‐ and photochromism. However, the analogue BTB‐2, in which the dimethylthiophene substituents are relocated to the 5,6‐positions of benzothiadiazole, does not show any detectable photochromism. To the best of our knowledge, this is the first example of six‐membered bridge bisthienylethenes (BTEs) in which the photochromism can be controlled by the substitution position. The photochromism difference is elucidated by the analysis of resonance structure, the Woodward–Hoffmann rule, and theoretical calculations on the ground‐state potential‐energy surface. In a well‐ordered single‐crystal state, BTB‐1 adopts a relatively rare parallel conformation, and forms an interesting two‐dimensional structure due to the presence of multiple directional intermolecular interactions, including C? H???N and C? H???S hydrogen‐bonding interactions, and π–π stacking interactions. This work contributes to several aspects for developing novel photochromic BTE systems with fluorescence modulation and performances controlled by substitution position in different states (solution, organogel, and single crystal).     

Formation of photo-functional spiroxazine monolayers and their dielectric constant determination using surface plasmon resonance

Spiroxazine are of considerable interest as photochromic materials because of their application. On the other hand, surface plasmon resonance (SPR) is a well-known optical method for measuring optical constants of thin film. In this study, photochromic materials were used as self-assembled monolayers (SAMs) of newly synthesized spiroxazine derivatives. We used Fresnel equation (four-layer model) to determine the precise dielectric constant () of the photochromic monolayers. Structure changes of spiroxazine derivatives under UV-light irradiation resulted in the change of optical constants, the dielectric constant and thickness. The obtained results indicated that the ring opening of photochromic spiroxazine can lead to the decrease in the dielectric constant and thickness.     

Photoactive Polyoxometalate/DASA Covalent Hybrids for Photopolymerization in the Visible Range

The synthesis of TBA-DASA-POM-DASA , the first photoactive covalent hybrid polyoxometalate (POM) incorporating a donor–acceptor Stenhouse adduct (DASA) reverse photochrome, is presented. It has been evidenced that in solution the equilibrium between the colorless cyclopentenone and the highly colored triene conformers is strongly dependent not only on the nature of the solvent but also the countercations, allowing to tune its optical properties. This complex has been further associated to photochromic spironaphtoxazine cations, resulting in a material which can be activated by two distinct optical stimuli. Moreover, when combined with N-methyldiethanolamine, TBA-DASA-POM-DASA constitutes a performing photoinitiating system for polyethylene glycol diacrylate polymerization and under visible light irradiation, a promising result in a domain scarcely developed in POM chemistry.     

Photochromic Doped Sol-Gel Materials for Fiber-Optic Devices

Photochromic-doped sol-gel materials have been prepared by adding a spiropyran photochromic dye to a solution of ethoxy silane monomers containing non-reacting ethyl radicals. After polymerization, normal photochromism (i.e., colored material upon UV irradiation) is obtained in the resulting matrix. The sol-gel matrix hinders the organic molecule rotations, thus giving two stable states, which can be reversibly switched by UV and green-blue irradiation respectively.If these materials are attached to optical fibers, the properties of the light throughput may be modified. Simple fiber-optic/photochromic devices made of two optical fibers placed in a V-groove removable connector have been prepared. Once cured, these devices behave as optically addressed variable delay generators. The same devices can be used for preparing simple optical switches and routing systems.     

Family of site-selective molecular optical switches

[reaction: see text] We describe the design, synthesis, and characterization of a family of thiol-reactive optical switches for labeling proteins and other biomolecules. Site-selective introduction of photochromic probes within biomolecules is being used as part of a new approach for optical control of biomolecular interactions and activities within cells. The thiol-reactive photochromic probes described in this report include a spironaphthoxazine and five spirobenzopyrans. The location of the thiol-reactive group on the spirobenzopyran is different for each probe; this feature can be used to control the geometry of the optical switch within a bioconjugate. The photochromes undergo rapid and reversible, optically driven transitions between a colorless spiro (SP) state and a brightly colored merocyanine (MC) state. The MC absorption of a spironaphthoxazine conjugate is red shifted by more than 100 nm compared to the equivalent spirobenzopyran, which may be exploited for the independent control of the MC to SP transition for up to two different spironaphthoxazine and spirobenzopyran conjugates within the same sample.     

光致变色液晶材料研究进展

本文介绍了液晶相态和光致变色的基本原理,液晶材料在光学领域中的应用,光致变色化合物的光异构化反应对液晶光学性质的影响,以及光致变色液晶材料制备的进展。参考文献53篇。     

Preparation and Properties of Electrospun Sheath-core Modified-PMMA Nanofibers with Photoluminescence and Photochromic Functions

Multi-functional nanofibers are playing an important role in the optical field, and are widely used in fluorescence indication, product anti-counterfeit identification and smart clothing. Nanofibers with photoluminescence and photochromic functions are already attracting more interest from researchers. In this work, based on electrospun technology, the modified-PMMA nanofibers[PMMA=poly(methyl methacrylate)] with photoluminescence and photochromic functions were prepared through the design of the sheath-core structure(SCNFs 1-4). Compared with other samples, SCNF-4 shows outstanding photoluminescence and photochromic functions. SCNF-4 can produce green light and its fluorescence intensity and fluorescence lifetime can reach 7144 a.u. and 1031.32 μs, respectively. In photochromic functions, SCNF-4 can show purple in 1 min under the 365 nm ultraviolet light, and the color can be preserved for more than 4 h under the sunlight. When SCNF-4 is irradiated by far infrared light, the color of the samples can fade quickly in 40 s. Under the irradiation of ultraviolet light of different wavelengths, SCNF-4 can display multi-color fluorescence and achieve a reversible transition between white and purple. The design of the sheath-core structure realizes the complementarity of photoluminescence and photochromic functions of the electrospun modified-PMMA nanofibers, which is important to promote the wide application of multi-functional nanofibers in the optical field.     

Synergistic activation of photoswitchable supramolecular assembly based on sulfonated crown ether and dithienylethene derivative

Conformational regulation among two or more distant sites is not only one of the main pathways to accomplish multiple tasks in complex biological systems but also represents a powerful strategy to obtain stimuli-responsive supramolecular nanoconstructs with tailored physicochemical performance. We herein report the fabrication of a photochromic supramolecular assembly, which can be synergistically activated by the conformational regulation with bis(4,8-disulfonato-1,5-naphtho)-32-crown-8 and the...     

多功能光致变色化合物

有机光致变色化合物是一种新型有机功能化合物,可广泛应用于光存储、光开关和光转换器件等领域,本文综述近几年来双光致变色化合物体系及具有荧光性能、磁性能等多功能光致变色化合物体系的研究进展,并对有机光致变色化合物的研究应用做了展望。     

Remarkable mechanochromism and force-induced thermally activated delayed fluorescence enhancement from white-light-emitting organic luminogens with aggregation-induced emission

The development of organic materials with white-light emission and thermally activated delayed fluorescence (TADF) properties in the solid state remain a challenge. Herein, a series of white-light-emitting organic luminogens have been developed and are found to show aggregation-induced delayed fluorescence (AIDF) characteristics. The AIDF emitters present dual-emission consisted of prompt fluorescence and TADF in the crystalline state. Their white-light emissions can be easily tuned by altering the chemical structure and connecting position of the heterocyclic aromatic substituent. Under the stimuli of mechanical force and solvent vapor, the compounds exhibit remarkable and reversible mechanochromism, in which their emission colors are switchable between white and yellow. Upon grinding, they also display linearly tunable luminescence colors, as well as force-induced TADF enhancement, which may be associated with the more compact molecular packing and the restriction of intramolecular motions. The results from time-resolved emission scanning and theoretical calculation suggest that the dual-emission of the AIDF luminogens likely results from the twisted intramolecular charge transfer transitions of the molecules, and the reversible mechanochromism properties probably stem from the interconversion of the quasi-axial and the quasi-equatorial conformations.     

Recent developments in the field of metal complexes containing photochromic ligands: Modulation of linear and nonlinear optical properties

Organic photochromic molecules are important for the design of photoresponsive functional materials, as switches and memories. Over the past 10 years, research efforts have been directed towards the incorporation of photoresponsive molecules into metal systems, in order either to modulate the photochromic properties, or to photoregulate the redox, optical and magnetic properties of the organometallic moieties. This review article focuses on some of the recent work reported within the last few years in the area of organometallic and coordination complexes containing photochromic ligands for the photoregulation of optical and nonlinear optical properties. The first part is related to photochromic 1,2-diarylethene (DAE)-containing metal complexes, examples of mono- and multi-DAE metal-based will be discussed. The second part deals with metal complexes incorporating spiropyran and spirooxazine derivatives.