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PHOTOPHYSICS OF THE HIGHLY HINDERED MOLECULES STUDIED BY LASER PHOTOLYSIS

激光光解研究高位阻分子的光物理学

基本信息

批准号：
62470008
负责人：
HAMANOUE Kumao
金额：
$ 4.03万
依托单位：
Kyoto Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1989
项目状态：
已结题

项目摘要

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

将纳秒级红宝石激光器与由个人计算机控制的检测系统（多色仪、图像增强器与线性位置敏感探测器耦合）相结合，构建了一种方便的激光光解系统。利用该体系研究了高阻分子的光物理性质，得到了以下结果：(1)2,4,6-三异丙基二苯甲酮在77 K时的多组分磷光可以用多个构象的存在来解释。(2)在亚纳秒时间尺度上，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）的吸收光谱随时间逐渐向蓝移。这种谱移归因于T_1态构象的变化。(3)即使对于邻苯甲酰苯甲酸甲酯这样的非阻碍分子，在77 K时也存在两个T_1态。(4) 1,8-二-t-二甲基蒽醌、1,2,3-三-丁基蒽醌和1,2-二-t-丁基-3-三甲基硅蒽醌的磷光光谱异常宽，寿命短，只有几小时。这些不寻常的T_1状态或混合的npi^*-pi ^*特征归因于分子几何结构的扭曲。虽然1,8-二-丁基蒽醌的瞬态吸收光谱归属于反应中间体，但1,2,3-三-丁基蒽醌和1,2-二-丁基-3-三甲基硅基蒽醌的瞬态吸收光谱归属于三重-三重吸收。(5)尽管2,2,2-三氟乙醇（TFE）具有很强的氢键能力，但在77 K时，蒽醌、-卤代蒽醌、二苯甲酮、1-吲哚酮、黄酮和黄酮在TFE中的磷光光谱与在普通溶剂中的磷光光谱相同。相比之下，TFE/水中的磷光光谱可以用三态酮、TFE和水之间的络合物的形成来解释，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态pi pi^*和pi pi^*能级顺序互换的必要条件。(6)通过对9-二溴蒽和9,10-二溴蒽在不同温度下的荧光光谱和三重-三重态吸收光谱的测量，发现在低温下（特别是在77 K时），从最低激发单重态到T_1态的直接系统间交叉是填充T_1态的最重要过程。证实了蒽基自由基作为反应中间体是通过npi^*特征的高激发态产生的。少