Conformational studies of molecules in the excited triplet state by time-resolved Fourier-transform infrared spectroscopy

通过时间分辨傅里叶变换红外光谱研究激发三重态分子的构象

基本信息

批准号：
03453017
负责人：
TASUMI Mitsuo
金额：
$ 4.42万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

项目摘要

To perform this research project, a Fourier-transform infrared spectro-photometer with an asynchronous time-resolving capability has been used in combination with an infrared microscope. The use of an infrared microscope is mecessary to observe laser-induced spectral changes from a small spot in the solid sample irradiated by loosely focused laser pulses. The fumdamental line at 1064 nm of a continuous-wave Nd : YAG laser and its second harmonic at 532 nm are mixed in a nonlinear crystal (BBO) to generate the third harmonic at 355 nm. The highest power of the third harmonic is 15 mW under a Q-switched operation which gives pulses with 70 ns duration at a repetition rate of 2 kHz. The third harmonic thus obtained is used to excite molecules in a KBr disk placed on the sample stage of the infrared microscope. In measurements by using the above spectrophotometer at room temperature, some infrared bands assignable to acridine in the lowest excited triplet state have been observed. For other organic compounds tested, however, effects due to chemical reaction (presumably oxidation), local heating, and evaporation of the sample are sensitively detected. To suppress these side-effects, attempts have been made to cool the sample down to about 120 K in vacuum with a miniature cryostat, which can be placed on the sample stage of the infrared microscope. Either dry nitrogen of argon gas of high pressure is used as the coolant. By using this apparatus, laser-induced infrared spectral changes have been observed for various aromatic compounds such as benzophenone, 4-phenylbenzophenone, and benzylideneaniline. Even at 120 K,effects of local heating are observed, whereas evaporation of the sample and chemical reaction seem to be suppressed to a satisfactory degree. It is necessary to separate effects of the local heating from spectral changes arising from genuine phtophysical and photochemical processes.

为了执行该研究项目，将具有异步时间分辨能力的傅里叶变换红外分光光度计与红外显微镜结合使用。使用红外显微镜对于观察由松散聚焦激光脉冲照射的固体样品中的小点引起的激光引起的光谱变化是必要的。连续波 Nd: YAG 激光器的 1064 nm 基波线及其 532 nm 二次谐波在非线性晶体 (BBO) 中混合，产生 355 nm 三次谐波。在 Q 开关操作下，三次谐波的最高功率为 15 mW，该操作以 2 kHz 的重复率提供持续时间为 70 ns 的脉冲。由此获得的三次谐波用于激发放置在红外显微镜样品台上的 KBr 盘中的分子。在室温下使用上述分光光度计进行的测量中，观察到一些属于最低激发三重态吖啶的红外谱带。然而，对于测试的其他有机化合物，可以灵敏地检测到化学反应（可能是氧化）、局部加热和样品蒸发造成的影响。为了抑制这些副作用，人们尝试使用微型低温恒温器在真空中将样品冷却至约 120 K，该微型低温恒温器可放置在红外显微镜的样品台上。使用干燥氮气或高压氩气作为冷却剂。通过使用该装置，已经观察到各种芳香族化合物（例如二苯甲酮、4-苯基二苯甲酮和亚苄基苯胺）的激光引起的红外光谱变化。即使在 120 K 下，也观察到局部加热的影响，而样品的蒸发和化学反应似乎被抑制到令人满意的程度。有必要将局部加热的影响与真正的光物理和光化学过程引起的光谱变化分开。