CONTROL OF PHOTOCHEMICAL REACTIONS BY HYDROGEN BONDING

我们研究了氢键对光化学异构化效率和模式的影响。此外，还研究了一种新的光诱导氢原子转移产生互变异构体的方法。我们发现分子内氢键和溶剂的共同作用控制了具有吡咯环和喹啉环的烯烃光异构化的效率和选择性(1)。在苯中，由于分子内氢键，I发生了单向反*顺光异构化。因此，顺式i并没有发生顺式到反式的异构化，而是发生了分子内氢原子转移，形成了互变异构体，这一点通过观察具有相当大的斯托克斯位移的荧光发射得到了证实。另一方面，在甲醇中，通过分子间氢键的形成，顺式到反式异构化优于反式到顺式异构化。在2′-羟基查尔酮（II）中，基于激光瞬态光谱的结果，我们发现了由分子内氢原子在三重态转移诱导的单向顺*反式异构化。我们还发现了甲酰基对分子内氢键化合物行为的新影响；甲酰基的引入提高了氢原子转移的效率，得到了互变异构体。因此，在吡咯环上有甲酰基的2[2-（2-吡啶）乙基]吡咯-5-羧基III在分子内氢原子转移产生的互变异构体中表现出相当高的荧光发射量子效率，尽管量子链过程的观察表明，系统间向三重态的交叉也被加速。

We have investigated the effect of hydrogen bonding to control the efficiency and the mode of photochemical isomerization. Furthermore, novel photoinduced hydrogen atom transfer to give the tautomer have been studied.We found a co-operative effect of intramolecular hydrogen bonding and solvent to control the efficiency and the selectivity of photoisomerization in an olefin with a pyrrole ring and a quinoxaline ring (I). In benzene, I underwent one-way trans*cis photoisomerization due to the intramolecular hydrogen bonding. Thus, cis-I did not undergo cis-to-trans isomerization, but undergo intramolecular hydrogen atom transfer to give the tautomer as revealed by the observation of the fluorescence emission with considerably large Stokes-shift. One the other hand, the cis-to-trans isomerization prevails over trans-to-cis isomerization in methanol by making an intermolecular hydrogen bonding.In 2'-hydroxychalcone (II), we found a novel one-way cis*trans isomerization induced by the intramolecular hydrogen atom transfer in the triplet state based on the results by laser transient spectroscopy.We also found an novel effect of formyl group on the behavior of intramolecularly hydrogen bonded compound ; the introduction of the formyl group increased the efficiency of hydrogen atom transfer to give the tautomer. Thus, 2 [2- (2-pyridy) ethenyl] pyrrole-5-carboxaldehyde III with formyl group at the pyrrole ring exhibited considerably high quantum efficiency of fluorescence emission from the tautomer produced by intramolecular hydrogen atom transfer, although the intersystem crossing to the triplet state is also accelerated as revealed from the observation of the quantum chain process.