Preparation and photochemical properties of water-soluble polymers with pendant tris(2,2′-bipyridyl)ruthenium(II) groups. N-Ethylated copolymers of vinylpyridine and cis-bis(2,2′-bipyridyl)(4-methyl-4′-vinyl-2,2′-bipyridyl)ruthenium(II)

Abstract

Copolymers (1) with pendant [Ru(bipy)₃]²⁺-like centres (bipy = 2,2′-bipyridyl) were prepared by copolymerisation of 4-vinylpyridine (vp) and [Ru(bipy)₂(mvbipy)]²⁺(mvbipy = 4-methyl-4′-vinyl-2,2′-bipyridyl). By variation of the monomer feed ratios, copolymers with vp: Ru of 2:1,11:1, and 66:1 were prepared. Quaternisation of the vinylpyridine groups of (1) with ethyl bromide yields water-soluble copolymers (2). Copolymers (1) and (2) were characterised by ¹H n.m.r., u.v.–visible, and atomic absorption spectroscopy. Fluorescence spectra and the lifetimes of copolymers (2) in aqueous solution and the quenching of the excited states by oxygen and methylviologen (1,1′-dimethyl-4,4′-bipyridinium) have been measured. These data indicate that the excited-state properties are only slightly affected by polymer-binding whereas the accessibility of the excited state to quenchers is substantially reduced. Rates for photoreduction of methylviologen in the presence of N(CH₂CH₂OH)₃ sensitised by copolymers (2) have been compared to that sensitised by [Ru(bipy)₃]²⁺.