Fluorescence characteristics of bisphenol A in room temperature ionic liquids.

Room temperature ionic liquids (RTILs) are emerging as a new class of 'green' solvents for use in a wide range of chemical processes. RTILs can sensitize or quench fluorescence of organic chemicals and their interactions still remain unclear, especially for weakly fluorescent chemicals. Herein, we report the effects of six RTILs on the fluorescence behavior of bisphenol A (BPA). The fluorescence intensities (FIs) of BPA in a RTIL-acetonitrile system were significantly quenched compared to acetonitrile. The quenching effect was stronger for [CnMIM]BF4 than [CnMIM]PF6. A decreasing trend of fluorescence lifetime (FL) of BPA was observed for [C6MIM]PF6 (4.26 to 3.86 ns) and [C14MIM]PF6 (4.15 to 3.78 ns) with increasing RTIL concentrations in the range of 1-10 mM. The quenching mode was consistent with a static quenching mechanism based on the consistency of FL and FI results. The emission bands of BPA and RTILs did not interfere with each other when RTILs were used as the solvent. The investigated RTILs enhanced the FIs of strongly fluorescing chemicals (12.0 ~ 19.0-fold for norfloxacin and 6.1 ~ 8.5-fold for dansyl chloride), but quenched those of weakly fluorescing chemicals (BPA). These results demonstrate that RTILs have different fluorescent effects on organic chemicals with different fluorophores. The interactions between RTILs and BPA result from many factors in addition to viscosity, such as solvent electrostatic dielectric constant, refractive index, density, polarization and molecular interaction. These results provide a theoretical foundation for application of RTILs in the analysis of weakly fluorescing chemical.