Book Description

This dissertation, "Resonance Raman and Time-resolved Spectroscopic Studies of Selected Chlorobenzophenone and Fluoroquinolones" by Wen, Li, 李闻, 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: Nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy was used in this thesis to study the photoreduction reactions and the photochemistry of chloro-substituted benzophenone (ClBP) triplets. The 3-chlorobenzophenone (3-ClBP), 4-chlorobenzophenone (4-ClBP) and 4,4′-dichlorobenzophenone (4,4′-diClBP) triplets exhibit similar properties to the parent BP triplet. In isopropyl alcohol (IPA), the hydrogen abstraction reactions were observed for the 3-ClBP, 4-ClBP and 4,4′-diDlBP triplets. The diphenylketyl (DPK) radicals produced from the hydrogen abstraction reactions were observed and the recombination of the DPK and dimethylketyl radicals at the para-position was observed to form a light absorption transient (LAT) species. In MeCN: H2O/1:1 aqueous solutions, these DPK radicals were also observed but with a slower formation rate and the LAT species was produced by reaction with OH radicals. Density functional theory (DFT) calculations were employed to help identify the intermediates seen in the TR3 spectra and to help provide information about the vibrational motions of the molecules examined. The 2-Cl-DPK radical was also observed in the TR3 spectra obtained in an IPA solvent. However, the yield of the 2-Cl-DPK radical and the hydrogen abstraction rate was observed to be significantly lower than that of the other ClBP examined here under the same experimental conditions. The results DFT calculations show that the 2-chloro substituent changes the geometry and the electron density of the molecular orbitals of the BP triplet so that the 2-chloro substituent reduces the hydrogen abstraction ability the triplet state, which is different the hypothesis put forward by some previous studies that an electron-withdrawing group should increase the photoreduction ability of BP derivatives. Norfloxacin (NF) and Enoxacin (EN) are representative derivatives of Fluoroquinolones (FQ). There are four forms of NF and EN and these different forms can coexist in aqueous solutions. The UV-vis absorption and resonance Raman (RR) spectra of NF and EN have been obtained in neat acetonitrile (MeCN), MeCN: HClO4-H2O/1:1 (pH?1), MeCN: H2O/1:1 (pH?7.5) and MeCN: NaOH-H2O/1:1 (pH?13) solutions. The species observed in the spectra are assigned by comparison of the experimental spectra to the DFT calculated spectra and the vibrational modes are also described from the results of the DFT calculations. The absorption spectra of NF and EN obtained in MeCN: H2O/1:1 solutions show that some other species coexist with the tautomeric forms in the neutral aqueous solution. The RR spectra of the tautomeric forms of NF and EN were obtained by subtraction of the RR spectra of the neutral and anionic forms from the RR spectra of NF and EN in neutral aqueous solutions. The results suggest that NF and EN exists in neutral, anionic and tautomeric forms in neutral aqueous solutions. The time dependant DFT calculation results suggest that the fluorine atom has little contribution to the lowest unoccupied molecular orbitals of the different forms of NF and EN. DOI: 10.5353/th_b4807974 Subjects: Benzoates Organic compounds - Spectra Photochemistry Rama