Reversible Multistimuli‐Response Fluorescent Switch Based on Tetraphenylethene–Spiropyran Molecules

Two tetraphenylethene (TPE)‐functionalized spiropyran (SP) molecules with very similar structure were designed and synthesized. The two molecules exhibit aggregation‐induced emission (AIE) properties, as well as multistimuli‐responsive color‐changing properties, such as photochromism and acidchromism. The investigation of their different photochromic and acidchromic characteristics and dual‐response fluorescent switch during isomerization indicated that the different link position between TPE and SP will significantly affect the extended π‐conjugated system, resulting in completely different photochromic and acidchromic properties.     

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.     

In-situ crystal structure analysis and control of photochromism with dual-mode photoreactive soft crystals

Photochromic compounds are of great interest currently owing to their potential applications. Their three-dimensional structure must be clarified to understand the photochromism mechanism. In-situ X-ray crystal structure analysis is a powerful tool for determining the structure directly after the photochromic reaction. In this review, I discuss about solid-state photochromic compounds, their direct X-ray observation in the crystal form, and in-situ control of photochromism in “dual photoreactive soft crystals”, which is a novel approach.     

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.     

Crystal structure and photochromism of 1-phenyl-3-methyl-4-benzyl-5-one-pyrazole S-methyl thiosemicarbazone

A new organic photochromic compound containing pyrazolone-ring photochromic functional unit: 1-phenyl-3-methyl-4-benzyl-5-one pyrazole S-methyl thiosemicarbazone (PMBP-smtsc) was synthesized. The photochromic properties and photochemical kinetics of PMBP-smtsc have been studied by UV reflectance spectra under irradiation of 365 nm light. The crystal structure analyses of photocolored product show the photochromism is due to the photoisomerization from enol form to keto form through an intermolecular proton transfer.     

Photochromism of organometallic compounds with structural rearrangement

This article introduces photochromic properties together with structures of organometallic compounds that undergo photo-induced structural rearrangement. The aim of this review is to survey the research on photochromism by using organometallics which possess by their own nature the properties responsible for the photochromism such as bonding and structural fluxionality, electronic state fluctuation, and photochemically active characteristic in both solution and the solid state. Therefore, the organometallics which include the well-characterized organic photochromic moieties, considered to be derivatives of such kinds of organic photochromic compounds, are excluded in this article. Mono-, di-, and poly-nuclear organometallic compounds are presented based on the reaction types such as linkage isomerization, haptotropic rearrangement, and reorganization of metal–ligand and/or metal–metal bonds. Very recently, the crystalline-state photochromism is becoming an attractive field of photochromic chemistry. As a demonstrative example, the photochromism of organometallic rhodium dinuclear complexes having a dithionite ligand (μ-O₂SSO₂), which shows 100% reversible interconversion in the crystalline-state and have been developed in the authors’ laboratory, will be discussed.     

Carbazole N-substituent effect upon DTMA: stabilizing and photochromic modulating

Dithienylmaleimide derivatives 7–27 were synthesized by introducing N-substituted carbazole for photo-stabilizing purpose, and the structures were fully confirmed. The photochromism and photo-stability were recorded via UV–vis spectra. Only ortho compounds 8–17 with N-substituents on carbazole moiety showed escalated photochromic change, while compound 7 and the para counterparts 18–27 showed no appreciable photochromism. Additionally, compounds 8–18 exhibited good photo-stability except 17 under 254 nm irradiation. The unstability of 17 may probably due to overrunning hindrance. These photochromic patterns indicated that hindrance and electronic effect mutually paid a decisive influence on the photochromism and photo-stability, which potentially exploited a new way to construct novel photochromic materials with regulable and conceivable performance.     

A Room-Temperature X-ray-Induced Photochromic Material for X-ray Detection

A color change: X-ray-induced photochromic species are rare and can be used for detection of X-rays. A highly robust X-ray-sensitive material with the discrete structure of a metal-organic complex has been found to show both soft and hard X-ray-induced photochromism at room temperature. A new ligand-to-ligand electron-transfer mechanism was proposed to elucidate this photochromic phenomenon.     

Solvent effect on photochromism of a dithienylperfluorocyclopentene having diethylamino group

Some photochromic diarylethenes having polar substituents were synthesized, and their photochromic behavior was examined. They exhibited photochromism with the similar photoreactivity in a non-polar solvent. However, the photocyclization quantum yield of dithienylperfluorocyclopentene having diethylamino group was found to decrease in polar solvents. The yield in acetonitrile was estimated to be 60 times smaller than that in hexane. The yields determined in various solvents were found to be correlated with the solvent polarity parameter E_T(30). Such an effect was not observed in dithienylfluorocyclopentenes bearing methoxy or acetoxy group and in non-fluorinated dithienylcyclopentene bearing diethylamino group.     

Tetraphenylpyrazine-based AIEgens: facile preparation and tunable light emission

Research on aggregation-induced emission (AIE) has been a hot topic. Due to enthusiastic efforts by many researchers, hundreds of AIE luminogens (AIEgens) have been generated which were mainly based on archetypal silole, tetraphenylethene, distyrylanthracene, triphenylethene, and tetraphenyl-1,4-butadiene, etc. To enlarge the family of AIEgens and to enrich their functions, new AIEgens are in high demand. In this work, we report a new kind of AIEgen based on tetraphenylpyrazine (TPP), which could be readily prepared under mild reaction conditions. Furthermore, we show that the TPP derivatives possess a good thermal stability and their emission could be fine-tuned by varying the substituents on their phenyl rings. It is anticipated that TPP derivatives could serve as a new type of widely utilized AIEgen, based on their facile preparation, good thermo-, photo- and chemostabilities, and efficient emission.     

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.     

Synthesis and photochromism of novel unsymmetrical diarylethenes with an azaindole unit

A new class of unsymmetrical photochromic diarylethenes with an azaindole moiety has been firstly synthesized. Their properties, including photochromism, crystal structure, as well as fluorescence, were investigated systematically. The azaindole was connected directly to the central cyclopentene ring as a heteroaryl moiety and available to participate in the photoisomerization reaction. Each of the diarylethenes exhibited favorable photochromism, good thermal stability, remarkable fatigue resistance, and notable fluorescence switches in both solution and solid media. The substituents at the para-position of the terminal benzene ring affected evidently their properties: the electron-donating methoxy could be effective to enhance the cyclization quantum yield, while the electron-withdrawing cyano could shift the absorption maximum to a longer wavelength in both hexane and solid film. The results revealed that the introduction of azaindole moieties and different substituents played an important role in the photoisomerization process of these diarylethenes.     

Synthesis and spectral-kinetic investigation of fulgimide-based photochromic autocomplexes of the dinitroquinoline series

Two new hybrid compounds, which belong to autocomplexes of the dinitroquinoline series and contain an NH spacer and fragments of photochromic fulgimides as donor components, were synthesized. These autocomplexes were used as ligands in the synthesis of cobalt-containing metal chelates. The spectral-kinetic study revealed that these compounds exhibit photochromism. The introduction of photochromic fulgimide moieties into the autocomplexes has no substantial effect on the spectral properties of the latter but influences the kinetics of photochromic transformations by decreasing their efficiency. Chelate complexes of the hybrid compounds with cobalt ions are characterized by the lowest efficiency of photochromic transformations due to a decrease in the intensity of activating radiation as a result of its absorption by the dinitroquinoline moieties, which are not conjugated with fragments of photochromic compounds. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1409–1416, July, 2008.     

Characterization and study of photochromism of hydroxylated polyazomethines

Polymers having a photochromic and/or thermochromic backbone have been synthesized by the condensation of bissalicylaldehydes with diamines. Photochromic activity was studied for hydroxylated polazomethines (HPAM) in the solid state and as thin films at room temperature, −75 and −180°. HPAM showed thermochromic behaviour but not photochromism. The lack of photochromic activity is attributed to the polymeric chain and the moieties attached to the azomethine groups which may increase the potential energy barrier and thus prevent the formation of trans-keto photoproduct.     

Nonsymmetrical Dithienylethenes Bearing Dithieno[3,2‐b:2′,3′‐d]thiophene Units with Photochromic Performance in the Crystalline Phase

Four novel nonsymmetrical photochromic diarylethene compounds containing dithieno[3,2‐b:2′,3′‐d]thiophene units were designed and synthesized to investigate their photochromic properties. All these molecules adopt a photoactive antiparallel conformation in single crystals, as revealed by X‐ray crystallographic analysis, and exhibit excellent photochromism in solution as well as in the crystalline phase.     

Structure and solid-state photochromic properties of two new compounds with pyrazolone-ring

Two new organic photochromic compounds based on pyrazolone were synthesized and further characterized by elemental analysis, MS, IR spectra, and ¹H NMR spectra. The photochromic properties and photochemical kinetics of them have been studied by UV absorption spectra under irradiation of 365 nm light. The photochromism of pyrazolone derivatives in the solid state has been so far explained only in terms of the light-induced change of absorption and their crystal structures, which is caused by the shift of the tautomeric equilibrium between the enol and keto forms. In this work, their IR spectra have been measured before and after irradiation. Based on the IR spectra and crystal structure analysis, a reasonable mechanism was proposed, the photochromic phenomenon may be due to the photoisomerization from enol-form to keto-form through proton transfer.     

Cation-dependent pericyclic reactions of crown-containing photochromic compounds

The review is devoted to the photochromism of pericyclic reactions of crown-containing photochromic systems. The complex formation of photochromic crown ethers with metal cations has a substantial effect on both the spectral characteristics of molecules and occurrence of photochromic reactions. A possibility to create systems with photocontrolled complex-forming properties is an attractive feature of the novel systems.     

Photochromic Dithienylethene‐Containing Boron(III) Ketoiminates: Modulation of Photo‐Responsive Behavior through Variation of Intramolecular Motion

A series of dithienylethene‐containing boron(III) ketoiminates, as well as their corresponding β‐ketoimine ligands, have been synthesized and characterized. The photophysical, electrochemical, and photochromic properties of the compounds have been studied. Photocyclization has been found to be suppressed upon introduction of a phenyl substituent on the nitrogen atom of the β‐ketoiminate core, whereas photochromism could be observed by replacement of the phenyl substituent with a bulky mesityl group. It is believed that the steric effect of the mesityl unit restricts molecular rotation, resulting in such a prominent difference in the photochromic properties.     

3-烷基/对烷氧基苯基-3-羟基-联茚满烯二酮衍生物的合成，晶体结构与固态光致变色及光致自由基性质研究

本文合成了一系列3-烷基/对烷氧基苯基-3-羟基-联茚满烯二酮新化合物,并通过¹H NMR, IR, MS 和元素分析数据进行了结构表征,其中化合物1,5,6的结构通过单晶X-Ray衍射进行了确证。分别用固体紫外光谱和电子自旋共振光谱研究了化合物的光致变色性能和光致自由基性质,结果表明：该类化合物在200W高压水银灯光源照射下产生光致变色现象,同时具有光致自由基性质。本文还根据分子结构和及分子内的作用力讨论了性质与结构之间的关系。     

磺酸功能化的离子液体型多金属氧酸盐的光色性能

发现磺酸功能化离子液体型多金属氧酸盐(IL-POM)具有可逆光色性质,并在紫外光激发下,详细考察了[PyPS]_nH_3-nPW₁₂(n=1,3)(PyPs:吡啶丙磺酸盐)、[PyPS]₄SiW₁₂、[TEAPS]₃PW₁₂(TEAPS:3-(三乙胺基)丙磺酸盐)等样品的光致变色行为。 结果表明,磺酸化的IL-POM是一类弱的电荷转移多金属氧酸盐,但在紫外光激发下有机阳离子和POM阴离子间可以发生电子相互作用,实现W⁶⁺→W⁵⁺的还原,并形成稳定的电荷转移复合物,导致样品显色。 钨磷酸盐的光色性大大强于钨硅酸盐,且空气中避光放置可以消色。 但样品容易疲劳,着色-褪色重复性不好。 对光色机理的研究显示,有机阳离子中的-SO₃H基团作为电子供体参与了变色过程。 揭示了磺酸基团的电子供体作用,为设计电荷转移多金属氧酸盐和POM基光色材料提供了新的思路。