Highly efficient photosensitization of TiO2 with diimine(diketonato)ruthenium(II) complexes

Diimine ruthenium(II) complexes with β-diketonate ligands were synthesized. Photophysical and electrochemical properties of these complexes were investigated. The electron-donating strength of β-diketonate can be tuned by choosing alkyl substitutents of the diketones. The complexes examined showed excellent photosensitization ability toward TiO2. The photoelectrochemical cell sensitized with [Ru(dcbpy)2(dpmo)]Cl (dpmo=dipivaloylmethanato) showed a solar light-to-electricity conversion efficiency of 6.9%. Electronic absorption spectra of the complexes were assigned by a computational calculation of molecular orbital. Transition from HOMO−2 to the LUMO and LUMO+2, which come from diketonate ligand, play an important role for absorption spectra in the longer wavelength response.