Off-on/On-off Dual-Mode Hydrochromic Materials：Water-Induced Acidity Changes in the Microenvironment Regulate the Color Switching of Rhodamine Derivatives北大核心CSCD

Based on the phenomenon that rhodamine derivatives（4-N-acrylamide-（3',6'-bis（diethylamino）-spiro［isobenzofuran-1,9'-xanthene］-3-one）（AM-RhB）will open the lactone ring to display color or emit fluorescence under moderate acidic conditions（4. 425%） and fluorescence intensity modulation（>700） before and after stimulating with water,and good reversibility （> 5 times）. This work will provide a promising way for the development of new hydrochromic materials. © 2022, Science Press (China). All rights reserved.     

Chromism of chemical compounds

Chromism, generally a reversible color change of substances, finds vital applications in the fields of switching, catalysis, molecule binding, drug delivery and energy storage applications. Chromism is caused by the change of electronic, conformational, crystal or physical structure of materials due to heat, light, solvent/vapour, applied electric potential, etc. There have been observed different types of chromism such as thermochromism, photochromism, solvetochromism, electrochromism and many others from different compounds. Here in we have discussed different types of chromisms but in brief as inherited by various types of materials. Reversible multicolor chromism by metal halide formamidinium perovskite attests solvetochromism and thermochromism due to the hydrogen bonding. Tetrathiazolylthiophene compound shows mechanochromism because of the structural deformation. Chain length of ligand influences the chromism in copper complex. Gold cluster complex, boron complex, Bi₂WO₆ also display specific chromic performance. Phosphomolybdate – malachite green dye moiety (PMMG) displays hydrochromism because of bridged water molecules. N₂ (or O₂) binding to PMMG has recently been shown as an extension of hydrochromism phenomonon. Thus, this account on chromism from various materials is expected to attract the attention of researchers.     

Thioxanthylium Cations: Highly Reversible Hydrochromic Mate-rials with Tunable Color and Moisture Sensitivity

Hydrochromic materials, which change color in response to moisture, are highly sought-after due to some unique applications such as moisture detection, humidity monitoring, anti-counterfeiting, and sweat-pore mapping. We herein report a new thioxanthene-9-ols/thioxanthylium cations hydrochromic system. The hydrochromic thioxanthylium cations can be generated/regenerated by exposing a chemically stable thioxanthene-9-ol to trifluoroacetic acid (TFA). The intensely colored thioxanthylium cations can be chemically reverted to the colorless thioxanthene-9-ol. Interestingly, the conversion between thioxanthene-9-ol and its cation species was found to be highly reversible in most cases (up to 50 activation-deactivation cycles). The color and moisture-sensitivity of thioxanthylium cations were also validated to be tunable via functionalization of the thioxanthene core with different aliphatic and aromatic groups at its 9 or 2,7-positions. Finally, paper probes were prepared using solution-immersion and inkjet-printing techniques to demonstrate the system's potential applications in humidity sensing and anti-counterfeiting     

Synthesis, crystal structure and characterization of photochromic 1,2-bis{2-ethyl-5-[2-(1,3-dioxolane)]-3-thienyl}perfluorocyclopentene

A novel photochromic diarylethene, 1,2-bis{2-ethyl-5-[2-(1,3-dioxolane)]-3-thienyl}perfluorocyclopentene (BEDTP), was synthesized and its structure was determined by single-crystal X-ray diffraction analysis. Its photochromic and fluorescent properties were also investigated. The results showed that this compound exhibited reversible photochromism, changing from colorless to magenta after irradiation with UV light both in solution and in the crystalline phase. In hexane solution, the open-ring isomer of BEDTP exhibited relatively strong fluorescence at 400 nm when excited at 282 nm. The fluorescence intensity decreased along with the photochromism upon irradiation with 254 nm light and its closed-ring isomer showed almost no fluorescence.     

Photochromism of new diarylethenes bearing both thiazole and benzene moieties

A new class of photochromic diarylethenes bearing both thiazole and benzene moieties has been developed, and the effects of substitution on their properties, including photochromism, fatigue resistance, and fluorescence properties have been investigated. They exhibited good photochromism and functioned as a fluorescence switch upon alternating irradiation with UV and visible light both in solution and in PMMA film. The electron-donating substituents could significantly enhance the cyclization quantum yield and depress the cycloreversion quantum yield whereas the electron-withdrawing groups functionalized an inverse action for these diarylethene derivatives. Relatively big differences exist among the properties of these diarylethenes which may be attributed to the different substituent effects.     

Light‐Controllable Ionic Conductivity in a Polymeric Ionic Liquid

Polymeric ionic liquids (PILs) have attracted considerable attention as electrolytes with high stability and mechanical durability. Light‐responsive materials are enabling for a variety of future technologies owing to their remote and noninvasive manipulation, spatiotemporal control, and low environmental impact. To address this potential, responsive PIL materials based on diarylethene units were designed to undergo light‐mediated conductivity changes. Key to this modulation is tuning of the cationic character of the imidazolium bridging unit upon photoswitching. Irradiation of these materials with UV light triggers a circa 70 % drop in conductivity in the solid state that can be recovered upon subsequent irradiation with visible light. This light‐responsive ionic conductivity enables spatiotemporal and reversible patterning of PIL films using light. This modulation of ionic conductivity allows for the development of light‐controlled electrical circuits and wearable photodetectors.     

Coumarinyl(thienyl)thiazoles as new fluorescent molecular photoswitches

A number of new photochromic 3-(4-phenylthiazol-5-yl)-and 3-(4-hetarylthiazol-5-yl)- coumarins has been synthesized. These compounds possess properties of molecular photo- switches providing a reversible change of the fluorescence intensity in the visible region of the spectrum upon alternating irradiation of their solutions with the visible and UV light. Irradiation with the UV light (λ < 400 nm) leads to their electrocyclization and loss of fluorescence, whereas irradiation of the cyclic form with the visible light (λ < 400 nm) returns the system to the state with the original absorption and fluorescence spectra. Switching of fluorescence is also observed in polymer matrices.     

Unraveling Dual Aggregation-Induced Emission Behavior in Steric-Hindrance Photochromic System for Super Resolution Imaging

Unprecedented dual aggregation-induced emission (AIE) behavior based on a steric-hindrance photochromic system is presented, with incorporation one or two bulky aryl groups, resulting in different flexibleness. The dual AIE behavior of open and closed isomers can be explained by restriction of intramolecular rotation (RIR), restriction of intramolecular vibration (RIV), and intermolecular stacking. The large bulky benzothiophene causes restricted rotation, enhancing the emission of open form in solution and weak π–π molecular packing, thereby efficiently enhancing the luminescence performance in the solid state. With incorporation of two large bulky benzothiophene groups, BBTE possesses the most outstanding AIE activity, undergoing highly efficient and reversible off-to-on fluorescence in film upon alternating UV and visible light irradiation along with excellent fatigue resistance. The off-to-on fluorescent photoswitch is successfully established in super resolution imaging.     

AIE Ligand Constructed Zn(Ⅱ)Complex with Reversible Photo-induced Color and Emission Changes

Fluoran salicylaldehyde hydrazone metal complex(FSHMC)is a kind of recently reported photo-responsive system,which has the advantages of simple synthesis,multiple colors as well as distinct color change before and after UV light irradiation.However,the emission property of FSHMC is relatively unitary.In solid state,especially,only fluorescence quench is induced after UV light irradiation,which limits their applications.In this work,a typical aggregation-induced emission(AIE)moiety of tetraphenylethene(TPE)was introduced to the design of FSHMC.The obtained FSHMC,2-Zn,exhibited reversible color and fluorescence changes upon UV light irradiation.Due to the AIE feature of compound 2,2-Zn exhibited different emission changes upon UV light irradiation in THF and in solid matrix,because of the fluorescence resonance energy transfer(FRET)process from TPE moiety to rhodamine B moiety.     

Unraveling Dual Aggregation‐Induced Emission Behavior in Steric‐Hindrance Photochromic System for Super Resolution Imaging

Unprecedented dual aggregation‐induced emission (AIE) behavior based on a steric‐hindrance photochromic system is presented, with incorporation one or two bulky aryl groups, resulting in different flexibleness. The dual AIE behavior of open and closed isomers can be explained by restriction of intramolecular rotation (RIR), restriction of intramolecular vibration (RIV), and intermolecular stacking. The large bulky benzothiophene causes restricted rotation, enhancing the emission of open form in solution and weak π–π molecular packing, thereby efficiently enhancing the luminescence performance in the solid state. With incorporation of two large bulky benzothiophene groups, BBTE possesses the most outstanding AIE activity, undergoing highly efficient and reversible off‐to‐on fluorescence in film upon alternating UV and visible light irradiation along with excellent fatigue resistance. The off‐to‐on fluorescent photoswitch is successfully established in super resolution imaging.     

Progress in synthesis,photochromism and photomagnetism of biindenylidenedione derivatives

Biindenylidenedione derivatives simultaneously exhibit photochromism and photo-generated organic radicals upon irradiation with UV light in solid and/or crystalline state, and they may be used as potential bi-functional materials in optoelectronic devices. This review article deals with recent progress in synthesis, relationship between molecular structures and phototochromic and photomagnetic properties of this kind of compounds.     

Between Aromatic and Quinoid Structure: A Symmetrical UV to Vis/NIR Benzothiadiazole Redox Switch

Reversibly switching the light absorption of organic molecules by redox processes is of interest for applications in sensors, light harvesting, smart materials, and medical diagnostics. This work presents a symmetrical benzothiadiazole (BTD) derivative with a high fluorescence quantum yield in solution and in the crystalline state and shows by spectroelectrochemical analysis that reversible switching of UV absorption in the neutral state, to broadband Vis/NIR absorption in the 1st oxidized state, to sharp band Vis absorption in the 2nd oxidized state, is possible. For the one-electron oxidized species, formation of a delocalized radical is confirmed by electron paramagnetic resonance spectroelectrochemistry. Furthermore, our results reveal an increasing quinoidal distortion upon the 1st and 2nd oxidation, which can be used as the leitmotif for the development of BTD based redox switches.     

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.     

Light-Controllable Ionic Conductivity in a Polymeric Ionic Liquid

Polymeric ionic liquids (PILs) have attracted considerable attention as electrolytes with high stability and mechanical durability. Light-responsive materials are enabling for a variety of future technologies owing to their remote and noninvasive manipulation, spatiotemporal control, and low environmental impact. To address this potential, responsive PIL materials based on diarylethene units were designed to undergo light-mediated conductivity changes. Key to this modulation is tuning of the cationic character of the imidazolium bridging unit upon photoswitching. Irradiation of these materials with UV light triggers a circa 70 % drop in conductivity in the solid state that can be recovered upon subsequent irradiation with visible light. This light-responsive ionic conductivity enables spatiotemporal and reversible patterning of PIL films using light. This modulation of ionic conductivity allows for the development of light-controlled electrical circuits and wearable photodetectors.     

Photoswitching of conductance of diarylethene-Au nanoparticle network

A network composed of gold nanoparticles covered with diarylethene dithiophenols was prepared on an interdigitated nanogapped gold electrode to show the reversible photoswitching of the conductance due to the photochromism of the diarylethene molecules induced by UV and visible light.     

Photo-induced morphology transition of a multifunctional photochromic bisthienylethene molecule with switchable aggregation-induced emission

A novel multifunctional molecule BTE-CNPH was designed and synthesized by connecting 2-(3′,5′-bis(trifluoromethyl)-biphenyl-4-yl)-2-cyanovinyl group to both side of the bisthienylethene(BTE), which exhibited excellent aggregation-induced emission(AIE) and bistable photochromism. High-contrast(60) reversible fluorescence switching was achieved in the 1 D nanowires, solid of BTE-CNPH and also in a polymethyl methacrylate(PMMA) film loaded with 1% BTE-CNPH under the alternative irradiation by 365 nm and visible light. Interestingly, the nanowire-like assembly morphology of BTE-CNPH in aqueous tetrahydrofuran(THF) solution of specific concentration was observed to translate into amorphous pieces gradually upon prolonged irradiation by the 365 nm, accompanying with photo-tunable AIE emission.     

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.     

Preparation of photoluminescent nanocomposite ink toward dual-mode secure anti-counterfeiting stamps

Fluorescent photochromism has been applied as an attractive approach for the production of effective authentication substrates to show dual-mode secure encoding. In the current study, novel photochromic and fluorescent nanocomposite ink was developed to introduce a stamped film with strong dual-mode emission for anti-counterfeiting purposes. Inorganic/organic nanocomposite ink was developed from lanthanide-doped aluminate (LDA) dispersed in poly(acrylic acid)-based binder. To produce a transparent film, LDA must be dispersed well in the poly(acrylic acid)-based ink solution. The fluorescent and photochromic nanocomposite ink was stamped effectively onto cellulose documents followed with thermal fixation. Homogeneous fluorescent and photochromic layer was stamped onto paper surface providing a transparent look with the ability to switch to green beneath ultraviolet as illustrated by CIE Lab. The stamped documents were studied by photoluminescence spectra to show an absorption peak at 364 nm, and fluorescence band at 438 nm. The induced security encoding was transparent beneath visible light turning into visible greenish-yellow beneath ultraviolet light indicating a bathochromic shift. LDA was synthesized in the nanoparticle form and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The morphological properties of the stamped documents were examined by infrared spectroscopy (FTIR), scan electron microscope (SEM), EDS, and X-ray fluorescence (XRF). The stamped paper sheets displayed an efficiently reversible photochromism without fatigue under visible and ultraviolet lights. The rheologies of the prepared photoluminescent nanocomposite inks as well as the mechanical performance of the stamped sheets were investigated.     

Polysulfurated pyrene-cored dendrimers: luminescent and electrochromic properties

We have synthesized a novel class of dendrimers, consisting of a polysulfurated pyrene core with appended poly(thiophenylene) dendrons (PyG0, PyG1, and PyG2, see Scheme 1), which exhibit remarkable photophysical and redox properties. In dichloromethane or cyclohexane solution they show a strong, dendron-localized absorption band with a maximum at around 260 nm and a band in the visible region with a maximum at 435 nm, which can be assigned to the pyrene core strongly perturbed by the four sulfur substituents. The dendrimers exhibit a strong (Phi=0.6), short-lived (tau=2.5 ns) core-localized fluorescence band with maximum at approximately 460 nm in cyclohexane solution at 293 K. A strong fluorescence is also observed in dichloromethane solution at 293 K, in dichloromethane/chloroform rigid matrix at 77 K, and in the solid state (powder) at room temperature. The dendrimers undergo reversible chemical and electrochemical one-electron oxidation with formation of a strongly colored deep blue radical cation. A second, reversible one-electron oxidation is observed at more positive potential values. The photophysical and redox properties of the three dendrimers are finely tuned by the length of their branches. The strong blue fluorescence and the yellow to deep blue color change upon reversible one-electron oxidation can be exploited for optoelectronic devices.     

Unique photochromism of two solid-emissive boron difluoride-based diarylethenes with isomeric structures

Two solid-emissive boron difluoride-based diarylethenes with isomeric structures are synthesized and the boron-difluoride chromophores are one part of the photoisomerization units in both diarylethenes. These two diarylethenes show similar fluorescent properties in the solid state as in dilute chloroform solutions because intermolecular planar π-π interactions are significantly alleviated as verified by their X-ray single crystal structures. However, only one of these two diarylethenes exhibits typical reversible absorption and fluorescence changes upon UV or visible light irradiation, and their diverse response to light irradiation is investigated by X-ray single crystal analysis and also DFT calculation. The investigation presented here provides valuable insight into the designing and development of diarylethene-based fluorescent switches in the solid state.