Reaction Control of Photochemical Processes in Liquid Crystalline Phases

在液晶和双层膜体系中，人们试图控制光化学过程的反应速率，如能量转移和电子转移。(1)当矩形交流波(最高可达10；lt；V_(0-p)&gt；)作为客体分子作用于含有敏化剂和受体的液晶盒时，观察到了显著的电场效应。对敏化剂荧光寿命的测量表明，能量传递速率与电场无关。比较垂直方向和水平方向相对于液晶盒平面的强度变化时，电场效应完全改变了符号。因此，观察到的电场对敏化荧光的影响归因于受体通过…的跃迁偶极子的取向控制对于双层膜体系中的电子转移，利用卟啉紫精连接体系研究了外加磁场对激光诱导电子转移速率的影响。紫精猝灭光生分子内离子自由基对的反向电子转移速率在0.1T以上被显著抑制。此外，两亲性紫精分子组装有助于光诱导的分子内电子转移的电荷分离。利用含咔唑部分的双链两亲铵化合物构建了空穴传输系统，在激光激发下提供了极长的电荷分离态。所有这些现象都归因于排列的受体(或施主)单元的协同效应，这些单元允许电子(或空穴)通过电子交换机制迁移。较少

Attempts have been made to control reaction rates of photochemical processes, such as energy-transfer and electron-transfer, in liquid crystals and bilayer-membrane systems.(1) Remarkable electric field effects were observed with sensitized fluorescence intensities of a perylene derivative, when rectangular AC waves (up to 10 <V_(0-p)> ) were applied to liquid crystal cells containing a sensitizer and an acceptor (the perylene derivative) as the guest molecules. Measurements of the fluorescence lifetime of the sensitizer indicated that the rates of energy transfer were independent of the electric fields. The electric field effects completely changed the sign when the intensity variation detected at vertical direction was compared with that at the horizontal direction with respect to the plane of the liquid crystal cell. The observed electric field effects on the sensitized fluorescence were consequently ascribed to the orientation control of transition dipolemoment of the acceptor thro … More ugh molecular alignments of the liquid crystal.(2) As to the electron-transfer in bilayer membrane systems, effects of external magnetic fields on laser-induced electron-transfer rates were investigated by the use of porphyrin-viologen linked systems. Rates of reverse electron transfer in the photogenerated intramolecular ion radical pair, as originated from quenching of porphyrin triplet by viologen, were remarkably suppressed at above 0.1 T. In addition, amphiphilic viologen molecular assemblies were found to help charge-separation of the photoinduced, intramolecular electron transfer in sensitizer-acceptor linked system incorporated into the molecular assemblies. Construction of hole-transport system was also attempted by the use of double-chain ammonium amphiphile with carbazole moiety, which afforded extremely long-living charge-separated states on laser excitation. All of these phenomena were ascribed to cooperativity effects of aligned acceptor (or donor) units, which permit electron (or hole) migration via electron exchange mechanism. Less