Molecular models and IR spectra of asymmetric tetraalkyl phosphonium iodide ionic liquids

Equilibrium geometries and IR spectra were computed for five novel tetraalkyl phosphonium iodide ionic liquids with potential use as electrolytes in Grätzel type nanocrystalline solar cells. These studies indicate a relationship between ionic conductivity and computed dipole moments, P–I ionic bond distances and HOMO–LUMO energy gaps. The computed IR spectra are in excellent agreement with observed spectra. DFT with the B3LYP hybrid functional was used together with Stuttgart–Dresden (SDD) basis sets for geometry optimization and frequency analysis calculations.