Asymmetric Diarylethenes with Oxidized 2‐Alkylbenzothiophen‐3‐yl Units: Chemistry, Fluorescence, and Photoswitching

Abstract Reversibly photoswitchable diarylethenes (DAEs) with fluorescent closed forms are applied in biology‐ and material science‐related super‐resolution microscopy. Yet, their full photoswitchable capacities remain unrevealed and unexplored. Due to limitations in synthesis, only 1,2‐[bis‐(2‐ethyl‐1‐benzothiophene‐1,1‐dioxide‐3‐yl)]perfluorocyclopentenes with two identical or very similar aryl groups attached to C‐6 and C‐6′ have been prepared so far. DAEs with increased Stokes shifts related to asymmetric structures and the presence of “push–pull” substituents are introduced in the present study, and their switching power is studied. The new “simplified” asymmetric DAEs possess higher cycloreversion quantum yields, but lower emission efficiencies than their known analogs with extended π‐conjugation paths. Fatigue resistance in organic (acetonitrile and methanol) and aqueous solvents is studied, and the performance in reversible saturable optical fluorescence transition (RESOLFT) microscopy is evaluated. The push–pull structures show an outstanding increase in fatigue resistance, compared with a reference (H/H) diarylethene. Fatigue resistances on the order of thousands of cycles have been observed in acetonitrile solutions without exclusion of air oxygen. The structure–property relationships and facile preparation procedures enable rational design of DAEs applicable as photoswitchable fluorescent probes. A new setup and methodology for measuring switching performance of fluorescent DAEs are introduced.