Turn-on mode fluorescent diarylethenes: Control of the cycloreversion quantum yield

Turn-on mode fluorescence switching molecules are applicable to super-resolution fluorescence microscopy, such as PALM (photoactivation localization microscopy), STORM (stochastic optical reconstruction microscopy) or RESOLFT (reversible saturable (switchable) optical linear fluorescence transitions) microscopy. Here we report on a molecular design strategy to control the cycloreversion quantum yield of the turn-on mode fluorescent diarylethenes, 1,2-bis(2-ethyl-6-aryl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentenes. Diarylethene derivatives having ortho-substituted phenyl rings at 6- and 6′-positions of 1,2-bis(2-ethyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentene were synthesized and their photophysical and photochemical properties were evaluated. The ortho-substitution of the phenyl rings with fluorine or methyl groups decreases the extension of π-conjugation length, resulting in a small blue shift of the absorption spectrum and a substantial increase in the cycloreversion quantum yield from 10−4 to 10−2 without significant influence on the fluorescence quantum yield. Water-soluble derivatives having sodium sulfonate groups were also synthesized. These derivatives fulfill requirements necessary for the application to RESOLFT super-resolution fluorescence microscopy.