STEPWISE ASSEMBLY OF TRIS-HETEROLEPTIC POLYPYRIDYL COMPLEXES OF RUTHENIUM(II)

A general method for the synthesis of tris-heteroleptic ruthenium(II) complexes of the type [Ru(dcbpy)(dmbpy)-(ddtc)] (3) and [Ru(dcbpy)(dmb py) (NCS)(2)] (4) is reported, where the ligands (dcbpy = 4,4'-dicarbo xy-2,2'-bipyridine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine, and ddtc = diethyldithiocarbamate) are introduced sequentially. The complexes hav e been characterized by UV/visible, emission, IR, Raman and NMR spectr oscopies and cyclic voltammetry. The effect of pH on the absorption sp ectra and luminescence behavior of these complexes consisting of proto natable ligands has been investigated in a water/ethanol solvent mixtu re by pH titration. The dissociation of protons is in sequential steps (pK(a) = 3.5 and 1.8). The excited-state pK(a) values are more basic than the ground-state pK(a) values. Resonance Raman spectra of these c omplexes strongly suggest that the lowest-energy metal-to-ligand charg e-transfer transition bands are localized on the dcbpy ligand. The mol ecular crystal structure of 3 and the performance of these complexes a s charge-transfer photosensitizers in a nanocrystalline TiO2-based sol ar cell is discussed.