National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
Phys Chem Chem Phys. 2011 Mar 21;13(11):4919-27. doi: 10.1039/c0cp02016h. Epub 2011 Jan 10.
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.
通过轴选择性三重态能量转移，可以实现对液晶（LC）的高灵敏度光取向。将三重态光敏剂（磷光供体）添加到可光交联的聚合物中，该聚合物连接 E-肉桂酸酯侧链，可确保显著提高光灵敏度，从而产生聚合物膜的光学各向异性和表面辅助 LC 光取向。用线性偏振 365nm 光对掺杂三重态光敏剂的聚合物膜进行光辐照，选择性地激发三重态敏化剂，导致肉桂酸酯的光学各向异性，这是由于轴选择性三重态能量转移。通过用理论的 Perrin 公式分析磷光光谱，我们发现三重态能量转移在距三重态光敏剂约 0.3nm 的半径内是有效的。这种光取向聚合物膜不仅可以用于棒状 LC，而且可以用于盘状 LC 的表面辅助取向光控，即使曝光能量非常低也是如此。这种方法对于通过光取向技术进行高通量制造光学器件非常有利。
