The voltammetric reduction, deprotonation and surface activity of ruthenium photovoltaic sensitizers in acetone

The reductive voltammetry of the photovoltaic sensitizer [(H2-dcbpy)2Ru(NCS)2] (H2dcbpy=2,2ʹ-bipyridine-4,4ʹ-dicarboxylic acid) and [(H3-tctpy)Ru(NCS)3]- (H3-tctpy= 2,2ʹ:6ʹ,2ʹʹ-terpyridine-4,4ʹ,4ʹʹ-tricarboxylic acid) has been investigated in acetone. Significant surface interactions at both platinum and glassy carbon electrodes occur at 0.6 V prior to the reversible potential expected for ligand-based reduction process of the fully protonated acids. The origin of the surface interactions are attributed to the acid¯base behaviour of the compounds, combined with overall deprotonation and reduction to hydrogen, since repetitive cycling of the potential reveals well-defined reversible reduction processes in the negative potential range, resulting from formation of doubly deprotonated [(H-dcbpy-)2Ru(NCS)2]2and singly deprotonated [(H2-tctpy-)Ru(NCS)3]2-, respectively. The extent of the surface interactions has been estimated by electrochemical quartz crystal microbalance and chronocoulometric measurements. Under certain conditions, a thick conducting polymer consisting of several hundred monolayers is formed.