title: Highly sensitive photoalignment of calamitic and discotic liquid crystals assisted by axis-selective triplet energy transfer.
abstract: Highly sensitive photoalignment of liquid crystals (LCs) can be realized by axis-selective triplet energy transfer. Addition of a triplet photosensitizer (phosphorescent donor) into a photocrosslinkable polymer tethering E-cinnamate side chains ensures dramatic enhancement of photosensitivity to generate the optical anisotropy of polymer film and surface-assisted LC photoalignment. Photoirradiation of triplet photosensitizer-doped polymer films with linearly polarized 365 nm light for the selective excitation of triplet sensitizer gives rise to optical anisotropy of cinnamates as a result of axis-selective triplet energy transfer. By analyzing phosphorescence spectra with theoretical Perrin's formula, we find that triplet energy transfer is efficient within a radius of ∼0.3 nm from the triplet photosensitizer. Such photoaligned polymer films can be used for the surface-assisted orientation photocontrol of not only calamitic LC, but also discotic LC, even for extremely low exposure energies. The present procedure would be greatly advantageous for high-throughput fabrication of optical devices by photoalignment techniques.
authors.affiliation: National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan. FURUMI.Seiichi@nims.go.jp
authors.forename: Seiichi
authors.initials: S
authors.lastname: Furumi
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Ichimura