Turn‐On Fluorescent Photochromic Disulfonylarylthiophenes: Effect of Sulfone Groups on Fluorescence and Conversion

A series of diarylthiophenes containing sulfone groups were synthesized using selective sulfur oxidation of benzothiophene group by meta‐chloroperoxybenzoic acid at room temperature, and their photophysical and chemical properties were studied. These compounds exhibited good photochromic behavior with a good fatigue property under consecutive ultraviolet (UV) and visible irradiation. The ring‐closed form emitted fluorescence upon UV excitation and the wavelength of fluorescence varied depending on the substituent. Compounds 2 – 5 exhibited high conversion ratios, reaching 95% for compound 5 , the benzoyl derivative, under UV irradiation. This high conversion is thought to be due to the lower quantum yield of the ring‐opening reaction compared to the ring‐closing reaction.