Study on the oxygen quenching of photoexcited molecules by a thermal lens method at high pressure

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The main object of this reseach is to make the instrument for measurement of thermal lens signal at high pressure. The apparatus for thermal lens measurement at normal pressure has been accomplished and its performance was confirmed by the experiment on the anthracene compounds. The high pressure system consisting of high pressure pump, high pressure vessel with four optical windows and high pressure gauge was made, but the sample cell for high pressure is now being improved and the measurement at high pressure will be feasible in the new future.In the measurement at normal pressure, the occurrence of internal conversion beside intersystem crossing was found for non-fluorescent cabonylanthracenes. The ratio between internal conversion and intersystem crossing depended on the solvent. It has so far been thought that the nonradiative transition for anthracene compounds is only intersystem crossing. The new observation in this research is the first step to investigate the nature and mechanism for the very fast internal conversion. The thermal lens measurement at high pressure is expected to become an effective method because the pressure effect give a systematic information on the medium effect.In the measurement at normal pressure, the quantum yield of prcduction of singletoxygen was obtained for the quenching of excited anthracene compounds by oxygen. It was suggested for most compunds that singlet oxygen was not formed from the quenching of the excied singlet state and it was formed at more yields than 80% from the excited triplet state. It was confirmed that singlet oxygen was formed from the excited singlet state of 9cyanoanthracene. The medium dependence of the singlet oxygen production is intended to be investigeted by the pressure effect based on the thermal lens method at high pressure.