Photo-switchable dithienylethenes: threshold of the photoreactivity

The quantum yields of the photoinduced ring-closure and ring-opening reactions of a series of 1,2-dithienylperfluorocyclopentene derivatives have been determined in view of the development of materials for photonic applications based on these molecules. The reaction quantum yields as a function of the S0–S1 excitation energy exhibit clear threshold behavior and are otherwise little sensitive to the chemical nature of the substituent. A ground state energy difference between the two isomers of >1 eV is deduced from this data. Additional information on the reaction surface is obtained from the temperature dependence of the quantum yields of the ring-opening reaction.