Photoinduced Optical Anisotropy Based on Axis-Selective Triplet Energy Transfer and Thermally Enhanced Reorientation in a Photo-Cross-Linkable Liquid Crystalline Polymer Film

An axis-selective photosensitized reaction of a photo-cross-linkable liquid crystalline polymer film doped with a triplet photosensitizer (TPS) based on axis-selective triplet energy transfer achieved a thermally enhanced molecular reorientation of the film using linearly polarized (LP) 405 nm light. Four types of TPS4,4‘-(N,N ‘-bis(diethylamino))benzophenone (DBP), 4-(N-diethylamino)benzophenone (BP), 5-nitroacenaphthene (AN), and p-nitroaniline (pNA)were used to compare the efficiency of the axis selection of the energy transfer. In all cases, the photoreactivity of a film was generated when doping with less than 9 wt % of TPS. The quenching sphere played a role in the photoreactivity, while the photoinduced optical anisotropy depended on the type of TPS. The axis-selective photoexcitation of TPS and the polarization-preserved energy transfer to the photoreactive mesogenic groups dominated the photoinduced optical anisotropy as well as the thermal enhancement of the molecular reorientation.