Photochromism of new unsymmetrical isomeric diarylethenes bearing a pyridine group

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.

Magnetic sulfonated polysaccharides as efficient catalysts for synthesis of isoxazole-5-one derivatives possessing a substituted pyrrole ring, as anti-cancer agents

Four polysaccharides (chitosan, cellulose, starch, and pectin) were magnetized with magnetic iron oxide (Fe₃O₄) and then sulfonated (except pectin) with chlorosulfonic acid. The obtained solid acids were used as a catalyst in three-component reactions between N-substituted-2-formylpyrrole, hydroxylamine-hydrochloride, and β-keto esters for the synthesis of 4-(2-pyrrolyl) methylene-isoxazole-5-ones. The optimal catalyst system was selected and studied by IR, SEM, TEM and XRD methods. The diverse isoxazoline derivatives (obtained via a mild and simple approach) were also fully characterized by spectroscopic methods and screened for anti-cancer activities against HT-29 and MCF-7 colon and breast cancer and HEK 293 normal cells. The results revealed interesting anti-cancer activities.

Four magnetic polysaccharides containing acidic groups were used as catalysts for the synthesis of 4-(2-pyrrolyl) methylene-isoxazole-5-ones. The products showed anti-cancer activities.

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.

Multi-responsive photochromism of a new diarylethene with a salicylaldehyde group

A new photochromic diarylethene with a salicylaldehyde group was synthesized and fully characterized. With the stimulation of acid/base and light, the diarylethene showed multi-responsive photochromism. The deprotonated derivative of the diarylethene with salicylaldehyde group, due to the addition of triethylamine into its solution, also showed excellent photochromism with distinguishable color change. And the deprotonated example could recover its original state with trifluoroacetic acid. Furthermore, the processes of photochromism and acidichromism could be effectively modulated with light and chemicals. Cyclic voltammetry tests suggested that triethylamine could significantly decrease band-gaps of both open-ring and closed-ring isomers of the diarylethene.

Synthesis, Crystal Structure and Photochromic Properties of a New Unsymmetrical Diarylethene

A new unsymmetrical diarylethene bearing a pyridine group, 1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(2-pyri-dyl)-3-thienyl]perfluorocyclopentene (3o), was synthesised and its structure determined by single-crystal X-ray diffraction analysis. This diarylethene exhibits excellent photochromic properties by alternate irradiation with UV and with visible light. Diarylethene 3o dissolved in hexane or embedded in a poly(methyl methacrylate) (PMMA) amorphous film showed good fluorescence switching properties. In the photostationary state, the fluorescence intensity can be quenched to 20% in hexane and to 29% in PMMA.