Spectroscopic properties of fluoroquinolone antibiotics and nanosecond solvation dynamics in aerosol-OT reverse micelles

Among fluoroquinolone antibiotics, ofloxacin (OFL) and norfloxacin (NOR) ha ve piperazinyl groups but flumequine (FLU) does not have this substitutent. The emission spectra of OFL and NOR are strong, broad structureless bands with large Stokes' shifts in water but the emission intensities are very we ak in organic solvents. Thus we find that these compounds exist as differen t chemical species in various solvents, A continuous red shift in the emiss ion bands for OFL and NOR is observed as the water concentration within the aerosol-OT (AOT; sodium 1,4-bis[2-ethylhexyl]sulfosuccinate) micelle incre ases or temperature of this solution rises. From the fluorescence anisotrop y measurements of OFL and NOR, we assume the intramolecular charge transfer after excitation from the nitrogen of the piperazinyl group to the keto ox ygen, Theoretical calculations further support this observation. Multifrequ ency phase and modulation experiments and time-resolved emission spectra cl early show the occurrence of intramolecular charge transfer and the subsequ ent nanosecond water reorganization around OFL or NOR in the AOT micelle. U pon increasing the water concentration within the AOT micelle, the relaxati on rate increases because of the large amount of free water. The emission s pectra of FLU do not exhibit any significant response to the physical prope rties of their environment.