Radiation-Induced Coloration of Photochromic Dithienylethene Derivatives

The radiation sensitivity of photochromic 1,2-dithienylethenes was studied with the aim to develop a new reusable color dosimeter. Upon γ-irradiation, crystalline colorless 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene turned red, and the absorption intensity increased linearly with the absorbed dose. The red color was bleached by visible-light irradiation and the crystal could be reused. On the other hand, crystalline 1,2-bis(2-methyl-1-benzothiophen-3-yl)perfluorocyclopentene did not show any radiation-induced coloration. The radiation sensitivity in solution was also examined to understand the possible applications to solution and film color dosimeters. Although radiation-induced coloration of the above two compounds was observed in benzene, no color change was detected in hexane, 2-methyltetrahydrofuran and n-butyl chloride. Excitation energy migration and transfer mechanism is considered to play a role in the coloration process in benzene.