The photoorientation movement of a diarylethene-type chromophore

We quantified coupled photoisomerization and photoorientation of a diarylet hene-type chromophore in films of poly(methyl methacrylate). We found that the chromophore retains partial memory of its orientation during the A -> B UV-induced isomerization and that the chromophore movement is thermalized after the A<-B green light induced isomerization. The isomerization quantum yields are <phi>(365)(AB) = 1.1, phi (405)(AB) = 0.32, and phi (532)(BA) = 0.16, and the transitions at 365 (405) and 532 nm of the B isomer are orie nted at an angle of 74.3 (61.3)degrees to each other. This relative orienta tion of the transition dipoles is rationalized by MOPAC molecular orbital c alculations.