PHOTOPHYSICS OF THE HIGHLY HINDERED MOLECULES STUDIED BY LASER PHOTOLYSIS

将纳秒红宝石激光器与由个人计算机控制的检测系统(多色仪和像增强器与线性位置灵敏探测器耦合)相结合，构成了一种方便的激光光解系统。(1)2，4，6-三异丙基二苯甲酮在77K时的多组分磷光可以用几种构象的存在来解释。(2)由2，4，6-三异丙基二苯甲酮在室温溶液中的最低三重态(T_1)引起的三重态-三重态吸收光谱在亚纳秒时间尺度上随时间逐渐向蓝移。这种光谱位移归因于T_1态的构象变化。(3)即使是像邻苯甲酰苯甲酸甲酯这样的非受阻分子，在77K也观察到两个T_1态的存在。(4)1，8-二叔丁基安息香醚…的磷光光谱较多的1，2，3-三叔丁基-1，2-二叔丁基-1-3-三甲基硅基-1，3-三甲基-硅基-1，2-三丁基和1，2-二叔丁基-1，3-三甲基硅基蒽醌的寿命较短，仅有几个单位。Pi pi^*或npi^*-pi pi^*混合性质的这些不寻常的T_1态被归因于分子几何结构的扭曲。虽然1，8-二叔丁基蒽醌的瞬时吸收光谱归属于反应中间体，但1，2，3-三丁基-1，2-三丁基-3-三甲基硅基蒽醌的瞬时吸收光谱归属于三重态吸收。我们还得到了以下结果：(5)尽管2，2，2-三氟甲醇(TFE)具有很强的氢键能力，但在77K时，其荧光光谱与通常溶剂中的相同。相反，在TFe/水中的磷光光谱可以用三线态酮、TFe和水形成的络合物来解释(S)，这表明纯溶剂性质(或性质)的变化并不总是分子本身固有的三重态pi^*和pi pi^*能级顺序互换的必要条件。(6)测量了9-和9，10-二溴并[9，10]-[9]-[9，10]-[9，10]-[9]-[9，10]-[9，10]-[9，10]-[9，10]-[9，10]-[9]-[9，10]-[9]-[9，10]-[9，10]-[9，10]-[9，10]-[9，10]-[9，10]-[9，10-二溴并[9，10]-[9，10]-[9，10]-[9，10]-[9]-[9]-[9]-[9]-[9]-[9]-[9]-[9]-[9，10]-[9，10-二溴并[9，10]-[9，10]-二溴并[9，10]-[9，10]-二溴并[9，10][9-二溴并[9，10]-[9，10]-二溴并[9，10]-[9，10]-二溴并[9，10]-二溴并[9，10]-二溴并[9，10]-二溴并[9，10]-二溴并[9，10]并[9，10]-二溴并[9，10]并[9]和[9，10]-二溴并[9，10]并[9(7)对于9-硝基并苯的上化学反应，证实了作为反应中间产物的蒽氧基是通过NPI的高激发三重态产生的。较少

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