Author Description

This dissertation, "Time-resolved Spectroscopic Studies of Photo-defluorination and Photo-decarboxylation Reactions of Selected Fluoroquinolone Antibiotic and Nonsteroidal Anti-inflammatory Drugs" by Tao, Su,, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: This thesis aimed to investigate the features and properties of the ground states, transient species and photoproducts involved in the photophysical and photochemical processes for four kinds of drug compounds: lomefloxacin (LF), norfloxacin (NF), tiaprofenic acid (TPA), and flurbiprofen (Fp). The investigation used femtosecond transient absorption (fs-TA), nanosecond transient absorption (ns-TA), UV/Vis absorption spectra (UV/Vis), nanosecond transient resonance Raman (ns-TR2) and nanosecond time-resolved resonance Raman spectroscopy (ns-TR3), as well as density functional theory (DFT) calculations. Although many previous investigations have indicated that photo-defluorination or photo-decarboxylation reactions may account for the phototoxicity for these compounds, detailed information on the mechanisms remains unclear. In this thesis, the photo-defluorination reaction of LF was explored in neutral water at pH 7.2. The fs-TA results revealed that the lowest lying excited singlet state species (S1) partially decayed into the ground state through fluorescence emission and partially underwent cleavage of the carbon-fluorine bond at position 8 to generate into a singlet aryl cation. Subsequently, intersystem crossing (ISC) allowing the transformation from singlet cation to triplet carbene was observed. Finally, a cyclization reaction with the N-ethyl