Laser photolysis study of anthraquinone in binary mixtures of ionic liquid [bmim][PF6] and organic solvent

Photochemical properties of the ionic liquid (RTIL) 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] and its binary mixed solutions with organic solvent (DMF and MeCN) were investigated by laser photolysis at an excitation wavelength of 355 nm, using anthraquinone (AQ) as a probe molecule. It was indicated that the triplet excited state of AQ (AQ*) can abstract hydrogen from [bmim][PF6]. Moreover, along with the change of the ratio of RTIL and organic solvent, the reaction rate constant changes regularly. Critical points were observed at volume fraction VRTIL = 0.2 for RTIL/MeCN and VRTIL = 0.05 for RTIL/DMF. For both systems, before the critical point, the rate constant increases rapidly with increasing VRTIL; however, it decreases obviously with VRTIL after the critical point. We conclude that the concentration dependence is dominant at lower VRTIL, while the viscosity and phase transformation are dominant at higher VRTIL for the effect of ionic liquid on the decay of rate constant.