Terpyridine- and 2,6-dipyrazinylpyridine-coordinated ruthenium(II) complexes: Synthesis, characterization and application in TiO2-based dye-sensitized solar cells

Two new ruthenium(II) complexes bearing terpyridine- or 2,6-dipyrazinylpyridine ligands have been prepared and characterized by one- and two-dimensional NMR techniques, ESI mass spectrometry, as well as by UV–vis, emission, FTIR, Raman, and cyclic voltammetry studies. The structure of the terpyridine-coordinated complex resembles that of black dye (tris(thiocyanato)(2,2′:6′,2″-terpyridyl-4,4′,4″-tricarboxylato)ruthenium(II) tris(tetra butylammonium) salt), while the spectral data of the 2,6-dipyrazinylpyridine-coordinated complex are consistent with an unanticipated, unsymmetrical binuclear structure. The ruthenium(II)/(III) oxidation potential of the terpyridine-coordinated dye was measured at +0.87 V (vs. Ag/AgCl), about 200 mV higher than the oxidation potential of black dye. According to a series of desorption experiments, both new dyes were found to adsorb on TiO2 to a greater extent than black dye. The photo-electrochemical properties of both dyes were investigated and compared to that of black dye; while the 2,6-dipyrazinylpyridine-coordinated complex was found to be a very poor sensitizer, the cells obtained from the terpyridine-coordinated dye show power-conversion efficiencies which are more than half of that attained by black dye. Finally, preliminary electron dynamics studies of the cells constructed with the terpyridine dye were carried out and the results are compared to that of black dye cells.