Ab initio study on the photochemical reaction of diarylethenes and the molecular design of novel diarylethenes

π共轭分子表现出广泛的光化学行为，在实验和理论上都引起了极大的兴趣。尽管人们做了大量的工作来阐明分子的光化学行为，但大多数的光化学行为还没有得到合理的解释。在本研究项目中，我们从理论上研究了二芳基乙烯的光化学行为，这是一种很有希望作为分子光记忆的物质。我们还研究了另一种π共轭体系的光化学。每个研究主题的实际结果如下：1)圆锥交叉(CIX)是了解二芳基乙烯光化学的最重要的成分。在目前的CASSCF计算中，发现CIX不具有对称性，而反应物和产物都具有C_2对称性。1)天青烯的S_1-S_0内转化是一个众所周知的违反卡沙定律的分子。50年来，人们从实验和理论上广泛地研究了天青烯的S_1-S_0内转换。在本研究中，我们首先指出，在CIX处，天青烯具有非平面结构。我们还考察了取代基对天青烯内转化过程的影响。

The π conjugated molecules, which exhibit a wide variety of photochemical behaviors, have been of great interest in experiments and theory. In spite of much effort to elucidate the photochemical behaviors, however, most of them have not been reasonably interpreted yet.In this research project, we theoretically examined the photochemistry of diarylethenes which are much expected as a molecular photo-memory. We also examined the photochemistry of another π conjugated system of azulenes. Actual results of each research theme are as follows.1) Conical intersection (CIX) for the photocyclization of diarylethene.The CIX is the most important ingredients to understand the photochemistry of diarylethene. In the present CASSCF calculation, it is found that the CIX has no symmetry, while both reactant and product has C_2 symmetry.1) S_1-S_0 internal conversions of azulenesAzulene is a well-known molecule which violates Kasha's rule. For 50 years, the S_1-S_0 internal conversion of azulene has been extensively examined experimentally and theoretically. In the present study, we first pointed out that azulene takes a non-planar structure at the CIX. We also examined the substituent effect on the internal conversion process of azulenes.