Copper(i) complexes of 6,6′-disubstituted 2,2′-bipyridine dicarboxylic acids: new complexes for incorporation into copper-based dye sensitized solar cells (DSCs)

Synthetic approaches to 6,6'-disubstituted-2,2'-bipyridine ligands bearing carboxylic acid substituents at the 4,4' or 5,5'-positions are described. Copper(I) complexes with these ligands have been prepared for use in copper-based dye-sensitized solar cells. The single-crystal structures of 6,6'-dimethyl-2,2'-bipyridine-4,4'-dicarboxylic acid (H(2)4), [H(3)6][CF3CO2].2CF3CO2H (H(2)6 = 6,6'-diphenyl-2,2'-bipyridine-4,4'-dicarboxylic acid) and 4[Cu(H(2)2)(H2)].3H2O (H(2)2 = 6,6'-dimethyl-2,2'-bipyridine-5,5'-dicarboxylic acid) are described, as well as those of the intermediates (1E,5E)-1,6-di(2-furyl)hexa-1,5-diene-3,4-dione and 4,4'-di(2-furyl)-6,6'-dimethyl-2,2'-bipyridine (3), and the copper(I) complex [Cu(3)(2)][PF6]. The roles that classical and non-classical hydrogen bonding and pi-stacking interactions play in determining the solid-state packing in these structures are discussed. Preliminary studies of DSCs with these complexes are reported.