Su Tao, Li Ming-De, Ma Jiani, Phillips David Lee
Department of Molten Salt Chemistry and Engineering, Shanghai Institute of Applied Physics, Chinese Academy of Sciences , 2019 Jia Luo Road, Jiading District, Shanghai 201800, P. R. China.
Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University , Guangdong 515063, P. R. China.
J Phys Chem B. 2017 May 4;121(17):4512-4520. doi: 10.1021/acs.jpcb.6b11267. Epub 2017 Apr 20.
The mechanism of the defluorination reaction(s) of lomefloxacin (LF) upon light illumination was investigated by using ultrafast laser flash photolysis combined with transient resonance Raman spectroscopy in near neutral water solution. The zwitterionic configuration of LF was determined to be the main species present in the near neutral water solution and was the species that was photoexcited to initiate the photochemical reaction. Femtosecond transient absorption revealed that the first excited singlet state (S) of LF did not appreciably undergo intersystem crossing (ISC), and instead partially decayed to the ground state via fluorescence emission, and there was partial cleavage of the carbon-fluorine bond at position 8 to produce a singlet LF aryl cation intermediate. The transient resonance Raman results provided a direct observation and vibrational spectral characterization of the singlet LF aryl cation species. Subsequently, the transformation from the singlet LF aryl cation to a triplet carbene via an ISC process was seen in nanosecond transient absorption spectra. Finally, the triplet carbene experienced a cyclization reaction with the N-ethyl chain to form a tricyclic product.
通过在近中性水溶液中使用超快激光闪光光解结合瞬态共振拉曼光谱，研究了洛美沙星（LF）光照脱氟反应的机制。确定LF的两性离子构型是近中性水溶液中的主要存在形式，并且是被光激发以引发光化学反应的物种。飞秒瞬态吸收表明，LF的第一激发单重态（S）没有明显发生系间窜越（ISC），而是通过荧光发射部分衰减到基态，并且8位的碳氟键发生部分断裂，生成单重态LF芳基阳离子中间体。瞬态共振拉曼结果提供了对单重态LF芳基阳离子物种的直接观察和振动光谱表征。随后，在纳秒瞬态吸收光谱中观察到单重态LF芳基阳离子通过ISC过程转变为三重态卡宾。最后，三重态卡宾与N-乙基链发生环化反应，形成三环产物。
