Reversibly Photoswitchable Fluorescent Diarylethenes Resistant against Photobleaching in Aqueous Solutions.

Low photostability in aqueous solutions is the main drawback of synthetic photochromic dyes, which limits their switching performance and utility in biology, medicine and life sciences. Even the most promising photochromes - reversibly photoswitchable diarylethenes (DAEs) with fluorescent "closed" forms - were known to undergo only several tens (typically 20-30) switching cycles in aqueous solutions. In this work, we introduce water-soluble and highly photostable 1,2-[bis-(2-ethyl/isobutyl-1-benzothiophene-1,1-dioxide-6-phenyl-3-yl)]perfluorocyclopentenes decorated with four -CONHC(CH2R)3 residues capped with 12 carboxylic acid groups (R = CH2CO2H or O(CH2)2CO2H). Under irradiation with UV- (365 nm) and visible light (470 nm), they provide several hundred (the "rapid" DAEs with isobutyl groups - up to thousand) full switching cycles in aqueous solutions without exclusion of air oxygen (outperforming the photoswitchable and fluorescent protein Dreiklang). The new branching approach based on secondary carboxamides with N-tert-alkyl residues decorated with polar groups may serve as a blueprint for the design of highly fatigue-resistant and reversibly photoswitchable fluorescent probes applicable in life sciences as aqueous solutions.