Proton-Gated Ring-Closure of a Negative Photochromic Azulene-Based Diarylethene

Proton-responsive photochromic molecules are attractive for their ability to react on non-invasive rapid optical stimuli and the importance of protonation/deprotonation processes in various fields. Conventionally, their acidic/basic sites are on hetero-atoms, which are orthogonal to the photo-active π-center. Here, we incorporate azulene, an acid-sensitive pure hydrocarbon, into the skeleton of a diarylethene-type photoswitch. The latter exhibits a novel proton-gated negative photochromic ring-closure and its optical response upon protonation in both open and closed forms is much more pronounced than those of diarylethene photoswitches with hetero-atom based acidic/basic moieties. The unique behavior of the new photoswitch can be attributed to direct protonation on its π-system, supported by 1H NMR and theoretical calculations. Our results demonstrate the great potential of integrating non-alternant hydrocarbons into photochromic systems for the development of multi-responsive molecular switches.

Synthesis strategies for non-symmetric, photochromic diarylethenes

Diarylethenes (DAEs) represent an important class of photochromes with notable characteristics, like thermally irreversible photoisomerization and high fatigue resistance. Structural diversification of the DAE scaffold has enabled further refinement of photochromic properties and realization of new applications, ranging from advanced materials to tools for studying biological systems. In particular, methods for synthesizing non-symmetric DAE scaffolds, which are typically more challenging to synthesize than their symmetric counterparts, have grown over the past 20 years. These developments are surveyed in this review, with discussion of how access to these compounds has contributed to the improvement of photochromic properties and paved the way for exploring new applications of DAEs. First, non-symmetric DAE structures are classified and their uses and applications are overviewed. Subsequent sections discuss the main strategies that have been used to access non-symmetric DAEs with examples illustrating the impact of non-symmetric DAEs in the growing field of light-controlled molecular systems.

A solvent-dependent chemosensor for fluorimetric detection of Hg2+ and colorimetric detection of Cu2+ based on a new diarylethene with a rhodamine B unit

A novel solvent-dependent chemosensor based on a diarylethene derivative for fluorescent “turn-on” recognition of Hg²⁺ and colorimetric detection of Cu²⁺ was synthesized, its multi-controllable photoswitchable behaviors with light and chemical stimuli were investigated.

Spectral properties and structure of unsymmetrical diarylethenes based on thiazole ring with hydrogen at the reactive carbon

Six new photoactive unsymmetrical diarylethenes bearing thiazole ring with hydrogen at the reactive carbon atom have been synthesized. Their structures have been studied by DFT calculations and X-ray crystallography. All compounds undergo irreversible photochemical transformations under irradiation with ultraviolet light, proceeding through the photocyclization stage. It has been found that only some normal (thiophene, imidazole and pyrazole derivatives) and inverse type (oxazole derivative) diarylethenes form colored photoinduced isomers under UV. In polar acetonitrile these intermediates show relatively fast irreversible thermal reaction, while in nonpolar toluene slow cycloreversion to initial diarylethenes is the predominant process of these species.

A Novel Indole-Containing Diarylethene: Synthesis, Crystal Structure and Photochromism

An indole-containing diarylethene with a trifluoromethyl function at the meta-position of the phenyl group attached to the thiophene moiety was synthesised. Its structure was determined by single-crystal X-ray diffraction analysis and its photochemical properties in solution and in the single crystalline phases were studied. The compound showed relatively high fluorescent modulation efficiency and cyclisation quantum yield.

Bisthienylethene Th2im and its complex (Th2imH)2[ReCl6]: crystalline-phase photochromism, and photochemical regulation of luminescence and magnetic properties

Molecular assembly of bisthienylethene Th2im (1) and [ReCl6]2− anions leads to the complex (Th2imH)2[ReCl6] (2), in which a [ReCl6]2(-) anion connects two equivalent Th2imH+ cations through Cl⋯N/C hydrogen bonds. Crystal structures of 1 and 2 indicate that two thiophene groups of each Th2im/Th2imH+ molecule adopt a photoactive antiparallel conformation. Thus, two compounds show crystalline-phase photochromism (CPP), i.e. reversible structural transformation between the open form and the closed form upon alternately irradiating the sample with UV light (365 nm) and visible light (574 nm for 1, 624 nm for 2). It was found that the CPP behaviors of 1 and 2 could regulate their luminescence and/or magnetic properties. Their solid-state emissions (433, 448, 482, 531 and 570 nm for 1, and 460, 489, 535 and 593 nm for 2) exhibited weaker intensities after UV irradiation with 365 nm light. Besides CPP and luminescence, compound 2 shows field-induced slow magnetic relaxation. Before and after UV irradiation, this compound revealed different magnetic behaviors, including the differences in the shape of the χMT vs. T plot, D parameter, and the values of the relaxation barrier Ueff and the preexponential factor τ0.

Substituent effects on the properties of photochromic hybrid diarylethenes with a naphthalene moiety

Four new unsymmetrical photochromic diarylethenes bearing both naphthalene and thiophene moieties were synthesized, and the structures of two diarylethenes were determined by single-crystal X-ray diffraction analysis. The naphthalene ring was connected directly to the central perfluorocyclopentene ring as an aryl moiety and available to participate in photoisomerization reaction. All the diarylethenes exhibited favorable photochromism and functioned as fluorescence switches in both solution and poly(methyl methacrylate) films. The electron-withdrawing substituent significantly shifted the absorption maxima to a longer wavelength and evidently suppressed the cycloreversion quantum yield, whereas the electron-donating substituents enhanced the fluorescence quantum yield of diarylethenes with a naphthalene moiety. Furthermore, cyclic voltammograms suggested that the oxidation onsets and band-gaps of the open-ring isomers were much bigger than those of the closed-ring isomers. The results indicated that the substituents at the 5-position of thiophene ring could availably modulate their optical and electrochemical behaviors.

Photochromism in sound-induced alignment of a diarylethene supramolecular nanofibre

A photochromic supramolecular nanofibre, composed of a diarylethene derivative, exhibits hydrodynamic alignment upon exposure to the audible sound.

Photoreversible current ON/OFF switching by the photoinduced bending of gold-coated diarylethene crystals

Gold-coated diarylethene crystals exhibited photoreversible bending upon irradiation with UV and visible light without any breaking of the gold layer.

Photomodulable phosphines incorporating diarylethene moieties

Incorporation of the dithienylethene moiety as a substituent provides new ‘switchable’ phosphine ligands whose electronic properties are reversibly modulated by light.

A photo- and halochromic multicolor switching system consisting of diarylethene and malachite green moieties

A diarylethene with a malachite green moiety was synthesized, and it showed multicolor states by photochromic and halochromic reactions.