Photoswitchable turn-on mode fluorescent molecules have been so far successfully used in super resolution fluorescence microscopies. Here, we report on fluorescence photoswitching of 1,2-bis(2-ethyl-6-phenyl-1b enz othiophene- 1,1- dioxide-3-y1) perfluoro cyclopentene (1) by irradiation with single-wavelength visible (420 nm < 2 < 470 nm) light, the wavelength of which is longer than the 0-0 transition of open-ring isomer la, without UV light excitation. By absorbing very weak hot bands or Urbach tails la underwent a cyclization reaction to produce fluorescent closed-ring isomer lb. Both cyclization and cycloreversion reactions of 1 took place with the visible light in the far off-resonance region of the absorption edge. Based on numerical simulations of the formation process of lb from la by irradiation with 450 nm light, weak absorption coefficients at 450 nm in n-hexane and CCl4 were estimated to be 0.084 and 0.19 M-1 cm(-1), respectively. The reversible fluorescence photoswitching with the single visible light is advantageously applicable to super-resolution fluorescence imaging in biological systems.