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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.

为了进行这项研究项目，傅里叶变换红外分光光度计与异步时间分辨能力已被用于与红外显微镜相结合。用红外显微镜观察固体样品在散聚焦激光脉冲照射下的小光斑的激光诱导光谱变化是必要的。利用连续Nd：YAG激光1064 nm的本底谱线与532 nm的二次谐波在非线性晶体（BBO）中混频，产生355 nm的三次谐波。三次谐波的最高功率为15 mW下的Q开关操作，这给出了脉冲与70 ns的持续时间在2 kHz的重复率。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。在室温下用上述分光光度计测量时，观察到了一些可归属于吖啶最低激发三重态的红外带。然而，对于测试的其他有机化合物，由于化学反应（可能是氧化），局部加热和样品蒸发的影响被灵敏地检测到。为了抑制这些副作用，已经尝试在真空中用微型低温恒温器将样品冷却到约120 K，该低温恒温器可以放置在红外显微镜的样品台上。使用高压氩气或干燥氮气作为冷却剂。利用该装置，对二苯甲酮、4-苯基二苯甲酮和亚苄基苯胺等芳香族化合物进行了激光诱导红外光谱的研究。即使在120 K，局部加热的效果进行观察，而蒸发的样品和化学反应似乎被抑制到一个令人满意的程度。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。