Selective fluorescence quenching of polycyclic aromatic hydrocarbons by nitromethane within room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Abstract

Recently discovered room temperature ionic liquids (RTILs) show tremendous promise to replace volatile organic compounds (VOCs). Investigation of these RTILs as solvents is in the very early stages. Before the full potential of these RTILs is realized, much more information about them as solvent systems must be obtained. The applicability of one such RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF6), as a solvent toward analysis for polycyclic aromatic hydrocarbons (PAHs) is explored. The steady-state emission behavior of six PAHs along with the fluorescence quenching by nitromethane within BMIM PF6 is investigated. The steady-state emission of six PAHs showed a bathochromic shift in BMIM PF6 compared to acetonitrile, indicating possibly a more dipolar environment. Further, the nitromethane quenching of PAH emission strongly suggests a selective nature as the emission from alternant PAHs are quenched while that from nonalternant PAHs is not. The PAH–nitromethane quenching behavior within BMIM PF6 is compared with that observed in the polar aprotic solvent acetonitrile, and a polar and similar viscosity (to BMIM PF6) solvent system, 90wt.% glycerol in water. It is observed that the PAH–nitromethane quenching within BMIM PF6 and 90wt.% glycerol in water is less efficient than in acetonitrile. This observation is suggested to arise from solvent viscosity.