Synthesis and Characterization of Rhenium(I) 4,4’-Dicarboxy-2,2’-bipyridine Tricarbonyl Complexes for Solar Energy Conversion

Abstract The synthesis of a series of rhenium(I) tricarbonyl complexes containing 4,4'-dicarboxy-2,2'-bipyridine (dcbpy) and various halide or pseudohalide ligands is reported. Deprotonation of the carboxylates occurs in basic medium resulting in upfield 1H NMR shifts for the protons of the carboxyl groups attached to 2,2’-bipyridine. Metal-to-ligand charge transfer (MLCT) due to dπ → π* transitions systematically shift in the halide series from 382 nm for Re(dcbpy)(CO)3F to 436 nm for Re(dcbpy)(CO)3I. The compounds emit in the 600 – 650 nm region and have emission lifetimes greater than 50 ns. The solar energy conversion efficiency is less than 1% when TiO2- Re(dcbpy)(CO)3X, (X = F, CN, SCN, Br, I), photoanodes are used in Gratzel cells.