PHOTOPHYSICS OF THE HIGHLY HINDERED MOLECULES STUDIED BY LASER PHOTOLYSIS

将纳秒级红宝石激光器与微机控制的探测系统（多色仪、像增强器和线性位置敏感探测器）相结合，构成了一个方便的激光光解系统。利用该体系，我们研究了高位阻分子的电子物理，得到以下结果：（1）2，4，6-三异丙基二苯甲酮在77 K下的多组分磷光可以用多种构象异构体的存在来解释。(2)室温下，2，4，6-三异丙基二苯甲酮溶液的三重态-三重态吸收光谱在亚纳秒时间尺度上随时间逐渐蓝移.这种光谱移动归因于T_1态的构象变化。(3)即使对于邻苯甲酰苯甲酸甲酯这样的无位阻分子，在77 K时也观察到两个T_1态的存在。(4)1，8-二叔丁基蒽醌的磷光光谱 关于我们 1，2，3-三叔丁基蒽醌和1，2-二叔丁基-3-三甲基硅基蒽醌的寿命短于几μ s，具有π π ^* 或npi^*-π ^* 混合特征的T_1态是由于分子几何结构的畸变所致。虽然1，8-二叔丁基蒽醌的瞬态吸收光谱归属于反应中间体，1，2，3-三叔丁基蒽醌和1，2-二叔丁基-3-三甲基硅基蒽醌的瞬态吸收光谱归属于三重态-三重态吸收，我们还得到以下结果：（5）尽管2，2，2-三氟乙醇（TFE）具有很强的氢键作用，但蒽醌、β-卤代蒽醌、二苯甲酮、1-茚酮、在77 K时，黄酮和二氢黄酮在TFE中的溶解度与在常用溶剂中的溶解度相同。而在TFE/水体系中的磷光光谱可以用三重态酮、TFE和水之间形成络合物来解释，表明纯溶剂性质的改变并不总是分子自身固有的三重态pi pi^* 和pi pi^* 能级顺序互换的必要条件。(6)通过对9-和9，10-二溴蒽在不同温度下的荧光光谱和三重态-三重态吸收光谱的测量，发现在低温下（特别是在77 K），从最低激发单重态到T_1态的直接系间跃迁是布居T_1态的最重要过程。(7)在9-硝基蒽的光化学反应中，证实了作为反应中间体的蒽氧基自由基是通过具有npi^* 特征的高激发三重态产生的。少

Combining a nanosecond ruby laser with a detection system (a polychromator and an image intensifier coupled with a linear position-sensitive detector) controlled by a personal computer, a convenient laser photolysis system was constructed. Using this system, we studied the photophysics of highly hindered molecules and the following results were obtained: (1) Multiple-components phosphorescences of 2,4,6-triisopropylbenzophenones at 77 K could be interpreted in terms of the existence of several conformers. (2) Triplet-triplet absorption spectra due to the lowest triplet (T_1) states of 2,4,6-triisopropylbenzophenones in solutions at room temperature shifted progressively to the blue with time on the subnanosecond time scale. This spectral shift was ascribed to the conformational change in the T_1 states. (3) Even for such a non-hindered molecule as methyl o-benzoylbenzoate, the existence of two T_1 states was observed at 77 K. (4) Phosphorescence spectra of 1,8-di-t-dutylanthraquinome, … More 1,2,3-tri-t-butylanthraquinone and 1,2-di-t-buty1-3-trimethylsilylanthraquinone were abnormally broad with short lifetimes of a few mus. These unusual T_1 states of pi pi^* or mixed npi^*-pi pi^* character were ascribed to the distortion of the geometrical structure of molecules. Although the transient absorption spectrum of 1,8-di-t-butylanthraquinone was assigned to a reaction intermediate, those of 1,2,3-tri-t-butylanthraquinone and 1,2-di-t-buty1-3-trimethylsilylanthraquinone were ascribed to the triplet-triplet absorptions.We also obtained the following results: (5) In spite of a strong hydrogen-bonding ability of 2,2,2-trifltiorothanol (TFE), the phosphorescence spectra of anthraqtiinone, beta-halogenoanthraquinones, benzophenones, 1-indanone, flavone and flavanone in TFE at 77 K were identical with those in usual solvents. In contrast, the phosphorescence spectra in TFE/water could be interpreted in terms of the complex formation among triplet ketones, TFE and water(s), indicating that the change of the nature (or character) of pure solvents was not always the essential condition for interchanging the order of energy levels of triplet pi pi^* and pi pi^* states inherent to molecule itself. (6) From measurements of fluorescence and triplet-triplet absorption spectra of 9- and 9,10-dibromoanthracenes at various temperature, It was found that the direct intersystem crossing from the lowest excited singlet states to the T_1 states was the most important process to populate the T_1, state at low temperature (especially at 77 K). (7) For pliotochpmical reactions of 9-nitroanthracenes, it was confirmed that anthryloxy radicals as the reaction intermediates were produced via the higher excited triplet states of npi^* character. Less