Time-Resolved Spectroscopic Study of the Defluorination and Cyclization Reactions of Lomefloxacin in Water.
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 (S1) 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.
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.
Tao
T
Su
Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University , Guangdong 515063, P. R. China.
Ming-De
MD
Li
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University , Xi'an 710127, Shaanxi, P. R. China.
Jiani
J
Ma
Department of Chemistry, The University of Hong Kong , Pokfulam Road, Hong Kong, P. R. China.
David Lee
0000-0002-8606-8780
DL
Phillips
D003500:Cyclization; D024841:Fluoroquinolones / Q000737:chemistry*; D054879:Halogenation; D007834:Lasers; D010782:Photolysis; D013059:Spectrum Analysis, Raman; D013997:Time Factors; D014867:Water / Q000737:chemistry*
D024841:Fluoroquinolones; D014867:Water; C053091:lomefloxacin