Kwok Wai Ming, Guan Xiangguo, Chu Lai Man, Tang Wenjian, Phillips David Lee
Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, PR China.
J Phys Chem B. 2008 Sep 18;112(37):11794-7. doi: 10.1021/jp803099s. Epub 2008 Aug 22.
An ultrafast broadband transient absorption spectroscopic study of the direct photolysis of oxetane DMT-BP [which is the oxetane adduct of 1,3-dimethylthymine (DMT) with benzophenone (BP)] is presented. Previous nanosecond time-resolved absorption studies by other researchers observed that direct photolysis of such oxetanes results in a rare, adiabatic photochemical reaction to produce a triplet excited-state carbonyl species. However, the mechanism for this adiabatic photochemical reaction remained unclear for the reaction sequence of the bond scission and the intersystem crossing (ISC) because of the time resolution for the experiments, and this prompted us to further study its mechanism with ultrafast time-resolution. The ultrafast time-resolved spectra presented here indicate that the cycloreversion reaction occurs in a stepwise manner on a singlet excited-state, and then intersystem crossing (ISC) occurs to produce the triplet carbonyl product observed in the previously reported nanosecond time-resolved experiments.
本文介绍了对氧杂环丁烷DMT-BP（即1,3-二甲基胸腺嘧啶（DMT）与二苯甲酮（BP）的氧杂环丁烷加合物）直接光解的超快宽带瞬态吸收光谱研究。其他研究人员之前的纳秒时间分辨吸收研究观察到，此类氧杂环丁烷的直接光解会导致一种罕见的绝热光化学反应，生成三重态激发态羰基物种。然而，由于实验的时间分辨率，对于该绝热光化学反应中键断裂和系间窜越（ISC）的反应顺序，其反应机制仍不清楚，这促使我们用超快时间分辨率进一步研究其机制。此处给出的超快时间分辨光谱表明，环化逆反应在单重态激发态上以逐步方式发生，然后发生系间窜越（ISC），生成先前报道的纳秒时间分辨实验中观察到的三重态羰基产物。
