Ruthenium(II) thiocyanate complexes containing 4′-(4-phosphonatophenyl)-2,2′:6′,2"-terpyridine:: synthesis, photophysics and photosensitization to nanocrystalline TiO2 electrodes

Several polypyridyl ruthenium(II) complexes [Ru-II(ttp-PO3H)(LL)(NCS)], where ttp-PO3H = 4-(4-phosphonatophenyl)-2.2':6:2 "-terpyridine and LL = 4,4'-dimethyl-2,2'-bipyridine (dmpy), 1,10-phenanthroline (phen) or 2,2'-biquinoline (biquin), were synthesized and characterized. The three structurally analogous complexes show different sensitization to nanocrystalline TiO2 film electrodes with increasing activity in the sequence LL = biquin, phen, dmpy, the biquin derivative showing almost no sensitization. Investigations demonstrate that the localization of the excited electron of the complexes affects the electron injection efficiency. Results indicate that the excited electron should be localized on the ligand with adsorbent groups attaching to the electrode in the design of complex sensitizers. Evidence of the localization of the excited electron in the ruthenium polypyridine complexes is proposed.