Synthesis, spectral, electrochemical and photovoltaic properties of novel heteroleptic polypyridyl ruthenium(II) donor-antenna dyes

Abstract

A series of new heteroleptic Ru(II)(4,4′-dicarboxylic acid-2,2′-bipyridine)(bipyridyl donor-antenna ligand)(NCS)₂ complexes carrying different donor-antenna moieties was designed, synthesised and characterised. A general synthetic procedure was used for the covalent attachment of the donor-antenna units 1,3-di(2-thienyl)benzo[c]-thiophene (DTBT), trans-stilbene (tS) and 4-{2-[2-(2-methoxyethoxy)ethoxy]-ethoxy}-N,N-diphenylbenzenamine (TPA-EO) to 2,2′-bipyridine. First, a Vilsmeier-Haack reaction was applied to get the respective aldehyde-functionalised donor-antenna compounds which secondly reacted with 4,4′-bis(triphenylphosphonium-methyl)-2,2′-bipyridyl chloride under Wittig conditions to give the desired bipyridyl donor-antenna molecules. To create a dimethylamino (NMe₂) substituted donor-antenna compound a reaction between 4,4′-dimethyl-2,2′-bipyridine and Bredereck's reagent was carried out. The final Ru(II) complexes referred to as Ru-DTBT-NCS, Ru-tS-NCS, Ru-TPA-EO-NCS and Ru-NMe₂-NCS were obtained via one-pot reactions, starting from dichloro(p-cymene)ruthenium(II) dimer. The bipyridyl donor-antenna molecules as well as the complexes were fully characterised and their optical and electrochemical properties were studied in detail. Preliminary tests of the novel Ru(II)bis(bipyridyl)(NCS)₂ dyes in solid-state dye-sensitized solar cells under AM1.5G conditions (100 mW cm⁻²) yielded short-circuit current densities of 1.06, 2.15, 3.42 and 4.03 mA cm⁻², open-circuit voltages of 625, 635, 685 and 735 mV and fill factors of about 45% corresponding to overall efficiencies of 0.31, 0.58, 0.99 and 1.37% for Ru-DTBT-NCS, Ru-NMe₂-NCS, Ru-tS-NCS and Ru-TPA-EO-NCS, respectively.