Heteroleptic Ru(II)-bipyridine complexes based on hexylthioether-, hexyloxy- and hexyl-substituted thienylenevinylenes and their application in dye-sensitized solar cells

A series of eight Ru(II) heteroleptic complexes incorporating an ancillary [2,2′]bipyridine functionalised at the [4,4′] positions with one (M-type) or two (B-type) thienylenevinylenes (nTVs, n = 2 or 4) is reported. Three types of substitutions have been used for nTVs: hexylthioether, hexyloxy and hexyl. The characterisation of the half-sandwich intermediates and final complexes is provided. In particular, the half-sandwich complexes in the M-type series are obtained as a racemate, whereas the heteroleptic complexes consist of two regioisomers. Finally, these complexes have been tested as dyes in dye-sensitized solar cells (DSSCs). Counterintuitively, better performances were obtained for M-type complexes with shorter 2TV moieties. The best performing dye was the Ru(II) complex mono-functionalized with a 2TV moiety having an hexylthioether substitution (M2S), which achieved a maximum power efficiency of 2.77% under full sun illumination (AM1.5G standard conditions). The structure–performance relationship in DSSCs is discussed based on photovoltaic and electrochemical data and DFT-calculations.