Photocyclization/Cycloreversion Quantum Yields of Diarylethenes in Single Crystals

Photocyclization and photocycloreversion quantum yields of three diarylethene derivatives were determined in the single-crystalline phase. The former yields in the crystalline phase were twice as large as those in solution. This can be attributed to only photoreactive antiparallel conformers being packed in the crystals, while in solution both photoreactive antiparallel and photoinactive parallel conformers coexist in almost equal amounts. The quantum yields in the crystals were found to be extremely high and 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene ( 3a ) exhibited the quantum yield of unity (100%). The latter yield of the closed-ring isomer of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene ( 1a ) was similar to that in solution, while the yields of the closed-ring isomers of 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene ( 2a ) and 3a were higher than those in solution by a factor of 2 to 3. The high yields are attributable to the constrained conformation of the photogenerated closed-ring isomers in the crystal lattice.