Turn-On Mode Fluorescent Diarylethenes

Abstract

Turn-on mode highly fluorescent photochromic chromophores, which are initially non-luminous under irradiation with visible light but activated to emit fluorescence upon irradiation with UV light, have been developed. The chromophores are sulfone derivatives of 1,2-bis(2-alkyl-1-benzothiophen-3-yl)perfluorocyclopentene. The open-ring isomers undergo photocyclization reactions to produce the fluorescent closed-ring isomers upon UV irradiation. The fluorescent property of the closed-ring isomers was dramatically improved by introducing short alkyl chain substituents at 2- and 2′-positions and aryl substituents at 6- and 6′-positions of both benzothiophene-1,1-dioxide groups. The photogenerated closed-ring isomers of 6 having phenyl rings and 10 having thiophene rings emit brilliant green and red-orange fluorescence (Φf = 0.87 (6) and 0.78 (10) in 1,4-dioxane), respectively. Visible-light responsive ability and water solubility, which are indispensable for the application to biological systems, have been provided to the fluorescent photochromic diarylethenes by modifying the central ethene bridge and introducing hydrophilic myo-inositol groups. The photoswitchable fluorescent molecules can be applied to single-molecule tracking in real time as well as to super-resolution fluorescence microscopy.