O2 solvation cavity in voids of ionic liquids studied by the solvatochromic red shift of O2(1Δg) phosphorescence.

Abstract

Phosphorescence spectroscopy of singlet oxygen [=O2(1Δg)] was applied to study the solvation properties of small solute molecule, O2, in ionic liquids. Unlike conventional molecular solvents, the spectral red shift of the O2(1Δg) phosphorescence in ionic liquids from the gas phase was found to depend not only on the refractive indexof solvents but also on the vdW volume of anions. This unusual spectral shift of the O2(1Δg) luminescence is interpreted by considering the size of solvation cavities in voids, which is estimated by analyzing the free volume in ionic liquids. These results suggest the potential of the O2(1Δg) phosphorescence spectral shift measurement in the study of molecular-scale voids in ionic liquids.