Photochromism Based on the Reversible Reaction of Singlet Oxygen With Aromatic Compounds

Abstract The photolysis of the endoperoxides anthra-bisbenzothiopyran (ABTPO) and of benzobisthioxanthene (BTXPO) has been studied in the wavelength range from 333 to 248 nm. At Δ = 248 nm maximum quantum yields Qc of 0.09 (ABTPO) and 0.10 (BTXPO) are found for the photocycloreversion reaction. Besides photocycloreversion a rearrangement reaction takes place with quantum yields QR(248) of 0.013 for ABTPO and 0.018 for BTXPO. Furthermore the selfsensitized photooxygenation of ABT and BTX has been investigated in the concentration range from 10−5 to 10−4 M. The mean values of the quantum yield Qp were found to be 0.02 (ABT) and 0.05 (BTX). The results indicate that ABT and BTX and their corresponding endoperoxides are components of highly reversible photochromic systems.