The turn-on type fluorescent photochromism of diarylmaleimide-S,S,S’,S’-tetraoxide

In recent years, fluorescence-switchable molecules have garnered significant attention as fluorescent dyes for super-resolution fluorescence microscopy, which is increasingly demanded in the field of biochemical imaging. Among such molecules, diarylethene- S , S , S’ , S’ -tetraoxide derivatives have proven particularly promising due to their ability to achieve high contrast fluorescence switching. Diarylethenes incorporating perfluorocyclopentene as the ethene bridge have become the standard scaffold due to their excellent fatigue resistance and thermal stability. However, their inherently low polarity necessitates extensive functionalization with hydrophilic groups to render them suitable for use in aqueous environments, such as in fluorescent labeling for super-resolution fluorescence microscopy. To address this limitation, we designed a novel class of oxidized diarylmaleimide (DAM) derivative featuring a maleimide as the ethene moiety, offering increased polarity and synthetic flexibility. Specifically, DAM 1 , composed of 2,4-dimethyl-3-phenylthiophene and N -methylmaleimide, and its oxidized counterpart DAM 2 , bearing two S , S -dioxidized thiophene rings, were synthesized and characterized. DAM 1 exhibited reversible photochromism upon irradiation with 436-nm and 550-nm light, accompanied by weak turn-off fluorescence and a cyclization quantum yield that depended strongly on solvent polarity. In contrast, DAM 2 displayed switch between one-way and reversible two-way photoisomerization and exhibited turn-on fluorescence behavior. These findings suggest that DAM-based systems are promising alternatives to conventional perfluorocyclopentene-based diarylethenes for aqueous fluorescence imaging applications, owing to their improved polarity and tunable photoresponsive properties.