| Abstract
| - The photochemical phase-transition behavior of polymer liquid crystals(LCs) containing azobenzene moieties with strong donor−acceptorsubstituents has been investigated. Copolymers of a mesogen and adonor−acceptor azobenzene were prepared. Photoirradiation ofa thin film of the polymer LCs (100−200 nm thickness) in thenematic (N) phase caused an N-to-isotropic (I) phase transition dueto trans−cis photoisomerization of the azobenzenemoiety, and the N phase recovered rapidly when photoirradiation wasceased because of cis−trans thermal back-isomerization.Time-resolved measurements with a laser pulse (532 nm; 10 ns, fwhm)revealed that the N−I phase transition took place in 300 μs.The thermal recovery of the N phase in the polymer LC with a donor−acceptorazobenzene, which stabilized the LC phase, occurred in 8 ms at 146°C. This response of the recovery is 103 times fasterthan that of non-donor−acceptor azobenzene LCs. In a samplethat showed a smectic (S) phase, however, no photochemical phase transitionwas observed. These phenomena are interpreted in terms of the stabilityof the LC phase.
|
