Photosensitized charge separation using partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complex and viologen

Abstract

Photosensitized charge separation using metallopolymers with both a photosensitizer and an electron acceptor on the same polymer backbone has been investigated in methanol. These metallopolymers consist of the bis(2,2′-bipyridine)ruthenium(II) complex as the photosensitizer and alkylviologen as the electron acceptor linked covalently to the imidazolyl residues on partially quaternized poly(1-vinylimidazole) through a hexylene spacer (RuQPImC 6VC 16) or a butylene spacer (RuQPImC 4VC 16). The viscosity and luminescence studies showed that these polymers, having two luminescence maxima at 560 and 650 nm, underwent interpolymer interaction between alkyl side chains through van der Waals interaction with increasing concentration of the polymer. The interpolymer interaction was weak at low concentration of the ruthenium(II) complex ([Ru(II)]<ca. 2.0×10 mol dm −3), which hardly affected the luminescence properties, while at high concentration, it became strong, which led to acceleration of the quenching of ruthenium(II) complex residue with the viologen residue. For both the RuQPImC 4VC 16 and RuQPImC 6VC 16, the rates of viologen radical formation increased with increasing concentration of the ruthenium(II) complex residue in two stages. Such a unique dependence can be explained by the interpolymer van der Waals interaction. Furthermore, it was found that the interpolymer van der Waals interaction depended significantly on length of the alkylene spacer.