New Development in Nonradiative Transition by a Thermal Lensing Method at High Pressure

通过时间分辨热透镜测量三重态形成的量子产率，研究了第一激发单重态的无辐射跃迁机制。研究的第一组分子是蒽羰基化合物。9-乙酰基蒽的三重态产率在除醇类溶剂外的溶剂中近似为1，表明非辐射失活仅通过系间交叉进行，不存在内转换过程。与此相反，9-苯甲酰基蒽在甲基环己烷中的三重态产率为0.2，表明内转换是主要的非辐射过程，并且三重态产率强烈依赖于溶剂，显示出在极性溶剂中内转换贡献较小的趋势。此外，还发现了9-溴-10-苯甲酰基蒽、9-氰基-10-苯甲酰基蒽和9-萘甲酰基蒽等蒽羰基化合物的内转换现象，并建立了高压热透镜装置，测量了9-乙酰基蒽和9-苯甲酰基蒽在4000 atm的甲基环己烷中的热透镜信号。9-乙酰基蒽的三重态产率随压力增加而增加，并且该结果不能在理论上解释，因为三重态产率在1个大气压下已经是1。必须检查是否存在高压测量固有的问题。对9-苯甲酰基蒽的三重态产率随压力的增加而显著增加，表明内转化率的贡献随压力的增加而减小，而对乙酰基萘、苯甲酰基萘、乙酰基菲和乙酰基芘等羰基芳烃分子的常压测量则证实了内转化率的贡献。此外，发现9，10-二甲氧基蒽在极性溶剂中发生内转化。

The mechanism for the nonradiative transition from the first excited singlet state was investigated by determining the quantum yield of triplet state formation with a time-resolved thermal lensing. The first group of molecules studied was anthracene carbonyl compounds. The triplet yield for 9-acetylanthracene was approximately unity in solvents besides alcoholic solvents, indicating that the nonradiative deactivation proceeds only through intersystem crossing and the internal conversion process is absent. In contrast, the triplet yield for 9-benzoylanthracene was 0.2 in methylcyclohexane, indicating that the internal conversion is a main nonradiative process, and the triplet yield was strongly dependent on the solvent, showing a tendency that the contribution of internal conversion is smaller in polar solvents. The occurrence of internal conversion was also found out for anthracene carbonyl compounds such as 9-bromo-10-benzoylanthracene, 9-cyano-10-benzoylanthracene and 9-naphthoylanthracene.The instrument for thermal lensing at high pressure was constructed, and thermal lens signals were measured for 9-acetylanthracene and 9-benzoylanthracene in methylcyclohexane at pressures up to 4000 atm. The triplet yield for 9-acetylanthracene increased with pressure, and this result cannot be theoretically explained because the triplet yield is already unity at 1 atm. It must be examined whether the problem inherent to the measurement at high pressures is present. The triplet yield for 9-benzoylanthracene increased remarkably with pressure, indicating that the contribution of internal conversion is decreased by pressure.In measurements at a normal pressure for other carbonyl aromatic molecules such as acetylnaphthalene, benzoylnaphthalene, acetylphenanthrane and acetylpyrene, the contribution of internal conversion was confirmed. Further, the occurrence of internal conversion for 9,10-dimethoxyanthracene in polar solvents was found out.