Properties of ionic liquid confined in porous silica matrix.

Porous silica matrices of different pore sizes with confined ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) [BMIM] [PF(6)] were prepared by sol-gel technique using a tetraethyl orthosilicate (TEOS) precursor with an aim to study the changes in physico-chemical properties of ionic liquid on confinement. It is found that on confinement 1) melting point decreases, 2) fluorescence spectra shows a red shift and 3) the vibrational bands are affected particularly those of imadazolium ring, which interacts more with the walls of the silica matrix. Preliminary theoretical calculations suggest that SiO(2) matrix interact more with the heterocyclic group of [BMIM] cation than the tail alkyl chain end group resulting in significant changes in the aromatic vibrations.