Surface confinement and its effects on the luminescence quenching of a ruthenium-containing metallopolymer

Abstract

Luminescence quenching of the metallopolymers [Ru(bpy)₂(PVP)₁₀]²⁺ and [Ru(bpy)₂(PVP)₁₀Os(bpy)₂]⁴⁺, both in solution and as thin films, is reported, where bpy is 2,2′-bipyridyl and PVP is poly(4-vinylpyridine). When the metallopolymer is dissolved in ethanol, quenching of the ruthenium excited state, Ru^2+*, within [Ru(bpy)₂(PVP)₁₀]²⁺ by [Os(bpy)₃]²⁺ proceeds by a dynamic quenching mechanism and the rate constant is (1.1 ± 0.1) × 10¹¹ M⁻¹ s⁻¹. This quenching rate is nearly two orders of magnitude larger than that found for quenching of monomeric [Ru(bpy)₃]²⁺ under the same conditions. This observation is interpreted in terms of an energy transfer quenching mechanism in which the high local concentration of ruthenium luminophores leads to a single [Os(bpy)₃]²⁺ centre quenching the emission of several ruthenium luminophores. Amplifications of this kind will lead to the development of more sensitive sensors based on emission quenching. Quenching by both [Os(bpy)₃]²⁺ and molecular oxygen is significantly reduced within a thin film of the metallopolymer. Significantly, in both optically driven emission and electrogenerated chemiluminescence, emission is observed from bothruthenium and osmium centres within [Ru(bpy)₂(PVP)₁₀Os(bpy)₂]⁴⁺ films, i.e. the ruthenium emission is not quenched by the coordinated[Os(bpy)₂]²⁺ units. This observation opens up new possibilities in multi-analyte sensing since each luminophore can be used to detect separate analytes, e.g.guanine and oxoguanine.