© 2018 Elsevier Ltd Environment-sensitive fluorophores have been used as molecular probes to acquire physical and chemical information in microstructures. Here, we report on solvatochromism of a fluorescent diarylethene, which is switched by photoirradiation. A turn-on mode photoswitchable fluorescent diarylethene derivative, 1,2-bis(2-ethyl-6-(5-methylthiophen-2-yl)-1-benzothiophen-1,1-dioxide-3-yl)perfluorocyclopentene (1a), underwent a cyclization reaction upon irradiation with ultraviolet (UV) light to form fluorescent closed-ring isomer 1b. 1b dramatically changed the fluorescent color in response to solvent polarity, such as green in n-hexane, yellow in tetrachloromethane (CCl4), orange in dichloromethane (CH2Cl2), and red in dimethyl sulfoxide (DMSO), and showed high fluorescence quantum yields of 0.6–0.8 in these solvents. The fluorescent solvatochromism is ascribed to the intramolecular charge-transfer (ICT) character of 1b, which consists of electron-donating thiophene rings at both ends and central electron-accepting benzothiophene 1,1-dioxide groups. The analysis based on the Mataga-Lippert plot revealed that the difference in the dipole moments between the excited and ground states of 1b is as large as 12 D. Such a solvatochromic fluorophore with photoswitching ability can find potential applications in super-resolution fluorescence imaging of microscopic polarity in biological cells and materials.