Effects of pH and polarity on the excited states of norfloxacin and its 4′-N-acetyl derivative: A steady-state and time-resolved study

Abstract

The properties of norfloxacin (NFX) and its 4′-N-acetyl derivative (ANFX) are investigated in different pH aqueous solutions and H2O-CH3CN mixed solutions, to determine the effects of pH and polarity on their ground and excited states. The triplet states of NFX and ANFX are affected more by pH than by polarity. The pH dependence of the NFX and ANFX triplet states is likely due to the different quantum yields of different protonated forms. Steady-state fluorescence, time-resolved fluorescence, and laser flash photolysis experiments at different pH values provide clear evidence of the involvement of different intramolecular charge-transfer pathways in the singlet states of NFX and ANFX. The different electron-donating capacities of 1-N, 1′-N, and 4′-N under different conditions determine the major pathway.