The effect of the formyl group position upon asymmetric isomeric diarylethenes bearing a naphthalene moiety

Molecular photoswitches in aqueous environments

Molecular photoswitches enable dynamic control of processes with high spatiotemporal precision, using light as external stimulus, and hence are ideal tools for different research areas spanning from chemical biology to smart materials. Photoswitches are typically organic molecules that feature extended aromatic systems to make them responsive to (visible) light. However, this renders them inherently lipophilic, while water-solubility is of crucial importance to apply photoswitchable organic molecules in biological systems, like in the rapidly emerging field of photopharmacology. Several strategies for solubilizing organic molecules in water are known, but there are not yet clear rules for applying them to photoswitchable molecules. Importantly, rendering photoswitches water-soluble has a serious impact on both their photophysical and biological properties, which must be taken into consideration when designing new systems. Altogether, these aspects pose considerable challenges for successfully applying molecular photoswitches in aqueous systems, and in particular in biologically relevant media. In this review, we focus on fully water-soluble photoswitches, such as those used in biological environments, in both in vitro and in vivo studies. We discuss the design principles and prospects for water-soluble photoswitches to inspire and enable their future applications.

A colorimetric and fluorescent chemosensor for Hg2+ based on a photochromic diarylethene with a quinoline unit

A new colorimetric and fluorescent 'on-off' chemosensor, 1O, based on a photochromic diarylethene with a quinoline unit was designed and synthesized. The chemosensor 1O demonstrated selective and sensitive detection of Hg2+ ions in the presence of other competitive metal ions in acetonitrile. The stoichiometric ratio of the sensor 1O for Hg2+ was determined to be 1 : 1, and the limit of detection of the probe 1O was calculated to be 56.3 nM for Hg2+. In addition, a molecular logic circuit with four inputs and one output was successfully constructed with UV/vis light and metal-responsive behavior. ESI-MS spectroscopy, Job's plot analysis, and 1H NMR titration experiments confirm the binding behavior between 1O and Hg2+.

Substituent effect in the photochromism of two isomeric asymmetric diarylethenes having pyrrole and thiophene units

Two new asymmetric isomeric diarylethenes having pyrrole and thiophene units have been synthesized by one-pot reaction and characterized by single crystal X-ray diffraction analysis. The two prepared diarylethenes had disparate crystal structures, and they exhibited distinctly different photochromic behavior, both in solution and in the solid state. Their photochromism, fatigue resistance, and fluorescence were investigated systematically. The methyl group at the reactive carbon atom could significantly enhance the quantum yield of cyclization step and decrease the quantum yield of cycloreversion step, whereas a cyano group at the same position could notably suppress the photocyclization reaction and promote the photocycloreversion reaction. The results indicated that the substituent at the reactive carbon atom could readily modulate the optoelectronic and physical properties for these diarylethenes.

A highly selective fluorescent chemosensor for Fe3+ based on a new diarylethene with a rhodamine 6G unit

A new multi-functional diarylethene-rhodamine 6G derivative was synthesized; its colorimetric and fluorometric sensing ability for Fe³⁺/EDTA, TFA/TEA and switching behaviors induced by light were investigated.

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.

Synthesis, crystal structure and photochromism of new diarylethenes with a benzene moiety

Three unsymmetrical diarylethenes with both thiophene and benzene moieties were synthesized. Their crystal structures and photochromic features were investigated systematically to elucidate the substituent effects of the terminal phenyl group on photochromism. Computational studies were performed to provide further insight into their frontier molecular orbitals and spatial distributions of electronic density. Each compound exhibited favorable photochromism in hexane and functioned as notable fluorescent photo-switches with fluorescence quenching efficiency of ∼96% induced by the intensity change of UV/vis light. Among the three diarylethenes, the cyano group on the terminal phenyl group significantly decreased the distance of the two reactive carbon atoms and strengthened the intermolecular hydrogen bond stacking interactions, resulting in improved stability in crystal state. Furthermore, it exhibited a red-shifted absorption maximum, an enhanced molar absorption coefficient, cyclization quantum yield, and fluorescence quantum yield in solution.