Sulfhydryl-functionalized diarylethenes: synthesis, photoswitching, and fluorescent properties.

Sulfhydryl group (SH) plays important roles in reactions with various functional groups, especially in biologically active systems. Photoswitchable diarylethene (DAE) derivatives have demonstrated applications in many research fields. Among the many classes of diarylethene derivatives, thiol derivatives have not been extensively explored. In this study, we systematically synthesized and characterized a series of bis-thiol functionalized dithienylethene derivatives. The thiol groups in this series are attached directly to the thiophene, or through a phenyl or methylene linker. Each series incorporated both dithienyl cyclopentene and hexafluorocyclopentene bridges and total six thiol substituted diarylethenes were synthesized. Among the six sulfhydryl DAE derivatives, four compounds were synthesized for the first time. Due to the reactivity of the thiol, they were prepared and stored as the corresponding thiol acetates. The photoswitching properties of the acetylated thiol derivatives were characterized. Three new thiol derivatives exhibited intriguing 'turn-on' fluorescence behavior, where the open isomers are non-fluorescent, while the closed isomers display fluorescence. These compounds represent a new class of fluorescent diarylethenes that do not require additional fluorophores. The thiol functional group offers potential for biological conjugation reactions and application as fluorescent probes.