Effect of C-5 position on the photochemical properties and phototoxicity of antofloxacin and levofloxacin: A stable and transient study

The photochemistry of two structure-related fluoroquinolones (FQs), antofloxacin (ANT) and levofloxacin (LEV), was studied in aqueous solution using stable and transient methods. The properties for energy transfer and electron transfer of these two FQs were also studied. The transient absorption spectra of FQs were observed, and transient species were assigned. The LEV triplet state (3LEV⁎) spectra (λmax=610nm) were determined, whereas the transient absorption of ANT could not be observed. The decay rate constant of 3LEV⁎ via unimolecular attenuation, self-quenching, and quenching by oxygen was 3.2×105s−1, 6.72×108M−1s−1, and 1.01×109M−1s−1, respectively. A reasonable diagram showing the decay of 1FQs* consisting of various substituents at the C-5 position was proposed. The phototoxicity of LEV and ANT was investigated and compared. Insertion of an amino group at the C-5 position made ANT relatively photostable and non-phototoxic compared with LEV. [Display omitted] •Displaying the different phototoxic behaviors of antofloxacin and levofloxacin•Using DFT method to calculate the lowest singlet energy of these two chemicals•A reasonable diagram showing the decay pathways of singlets of is proposed.•Revealing the role of the substituents in C-5 position