CONTROL OF PHOTOCHEMICAL REACTIONS BY HYDROGEN BONDING

我们研究了氢键对控制光化学异构化效率和方式的影响。此外，我们还研究了光致异构化的新型氢原子转移，发现分子内氢键和溶剂的协同作用可以控制含吡咯环和喹恶啉环的烯烃的光异构化效率和选择性(I)。在苯中，由于分子内氢键的作用，我经历了单向的顺式光异构化。因此，顺式-I没有发生顺式到反式的异构化，而是发生了分子内氢原子的转移，得到了具有相当大斯托克斯位移的荧光发射的互变异构体。在2‘-羟基查尔酮(II)中，通过分子间氢键的形成，我们发现了分子内氢原子以三重态转移引起的一种新的单向顺反异构化反应。我们还发现了甲酰基对分子内氢键化合物行为的新的影响；甲酰基的引入提高了氢原子转移的效率，从而得到了互变异构体。因此，2-[2-(2-吡啶基)乙烯基]吡咯-5-甲醛III在分子内氢原子转移产生的互变异构体上表现出相当高的荧光发射量子效率，尽管量子链过程也加速了向三重态的跃迁。

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.