Synthesis, characterization and sensitization properties of two novel mono and bis carboxyl-dipyrido-phenazine ruthenium(II) charge transfer complexes

Abstract

Two novel heteroleptic ruthenium complexes of the type cis-[Ru(dppz-COOH) 2(NCS) 2] ( 1) and cis-[Ru(dppz-COOH)(phen)(NCS) 2] ( 2), where dppz-COOH = 11-carboxyl-dipyrido[3,2-α:2′,3′-c]phenazine and phen = 1,10-phenanthroline, were synthesized and fully characterized by analytical and spectroscopic techniques. The complexes showed a broad and intense metal-to-ligand charge transfer (MLCT) transition band in the visible region, which is emissive both in MeOH at room temperature and in a MeOH–EtOH glass (77 K). Both complexes 1 and 2 were anchored to nanocrystalline TiO 2 film electrodes and the resulting photoelectrodes were successfully incorporated in dye-sensitized solar cells (DSSCs) using a solid state redox electrolyte [PEO/TiO 2/I −/I 3 − (PEO = polyethyleneoxide, M W = 2 × 10 6)]. The photovoltaic performance of the DSSCs was evaluated and compared with the cell prepared with cis-(NBu 4) 2[Ru(Hdcbpy) 2(NCS) 2], so-called N719 dye (dcbpyH 2 = 4,4′-dicarboxy-2,2′-bipyridine). Although the efficiency of the 2-sensitized solar cell was 10% higher than the 1-sensitized solar cell, neither was as efficient as the N719-sensitized solar cell. The results obtained in the present article are consistent with the photochemical properties of the corresponding Ru(II) dyes.