Self assembled composites of luminescent Ru(ii) metallopolymers and the Dawson polyoxometalate α-[Mo18O54(SO4)2]4−

Abstract

The interaction of two luminescent metallopolymers; [Ru(bpy)₂(PVP)₁₀]²⁺ and [Ru(bpy)₂(CAIP)co-poly₇]⁺, where bpy is 2,2′-bipyridyl, PVP is polyvinylpyridine, and (CAIP)co-poly₇ is poly(styrene₆-co-p-(aminomethyl)styrene) amide linked to 2-(4-carboxyphenyl)imidazo[4,5-f] [1,10]phenanthroline, with the Dawson polyoxomolybdate α-[Mo₁₈O₅₄(SO₄)₂]⁴⁻ is described. Both metallopolymers undergo electrostatic association with the polyoxometalate. From both electronic and luminescence spectroscopy the thermodynamic products were determined to be {[Ru(bpy)₂(PVP)₁₀]_4.5[Mo₁₈O₅₄(SO₄)₂]}⁵⁺ and {[Ru(bpy)₂(CAIP)co-poly₇]₅[Mo₁₈O₅₄(SO₄)₂]}⁺, i.e. in both instances, the number of ruthenium centres in the cluster exceeds the number required for charge neutralization of the molybdate centre. Association quenches the luminescence of the metallopolymer although, consistent with the excess of Ru(II) present in the associated composites, emission is not completely extinguished even when a large excess of [Mo₁₈O₅₄(SO₄)₂]⁴⁻ is present. The observed emission lifetime was not affected by [Mo₁₈O₅₄(SO₄)₂]⁴⁻ therefore quenching was deemed static. The luminescent intensity data was found to fit best to a (sphere of action) Perrin model from which the radii of the quenching were calculated as 4.6 Å and 5.8 Å for [Ru(bpy)₂(PVP)₁₀]²⁺ and [Ru(bpy)₂(CAIP co-poly)₇]⁺ respectively. Both UV/Vis and resonance Raman data indicate the presence of a new optical transition centered around 490 nm for the composite, {[Ru(bpy)₂(PVP)₁₀]_4.5[Mo₁₈O₅₄(SO₄)₂]}⁵⁺ but not for {[Ru(bpy)₂(CAIP)co-poly₇]₅[Mo₁₈O₅₄(SO₄)₂]}⁺. This indicates strong electronic interaction between the metal centres in the former composite, which despite good thermodynamic analogy, is not observed for {[Ru(bpy)₂(CAIP)co-poly₇]₅[Mo₁₈O₅₄(SO₄)₂]}⁺. These results are consistent with photoelectrochemical studies of layer by layer assemblies of these films which indicate that the ruthenium centre sensitizes polyoxometalate photo-oxidation of benzyl alcohol in {[Ru(bpy)₂(PVP)₁₀]_4.5[Mo₁₈O₅₄(SO₄)₂]}⁵⁺ but not in {[Ru(bpy)₂(CAIP)co-poly₇]₅[Mo₁₈O₅₄(SO₄)₂]}⁺.