　Low photostability in aqueous solutions is the main drawback of synthetic photoswitchable fluorescent probes, which limits their use in biology, medicine and life science. In this study, we prepared water-soluble and highly photostable 1,2-[bis(2-ethyl/2-isobutyl-1-benzothiophene- 1,1-dioxide-6-phenyl-3-yl)perfluorocyclpentenes decorated with four -CONHC(CH₂R) residues capped with 12 carboxylic acid groups. Under irradiation with UV (365 nm) and visible light (470 nm), they provide several hundred (up to 1000) full switching cycles in aqueous buffer solutions without exclusion of air.