Harvesting light energy by iridium(iii) complexes on a clay surface

Abstract

Energy transfer was investigated between two types of iridium(III) complexes, [Ir(dfppy)₂(C_n-bpy)]⁺ (dfppyH = 2-(2′,4′-difluorophenyl)pyridine; C_n-bpy = 4,4′-dialkyl-2,2′-bipyridine; dialkyl = dimethyl (C₁), didodecyl (C₁₂), and dinonyldecyl (C₁₉)) and [Ir(piq)₂(C_n-bpy)]⁺ (piqH = 1-phenylisoquinoline) as a donor and an acceptor, respectively. The complexes were co-adsorbed by colloidally dispersed synthetic saponite. The efficiency of energy transfer (η_ET) was obtained from emission spectra at various donor-to-acceptor ratios (D/A) on the basis of the Förster-type energy transfer mechanism. For C₁-bpy, η_ET was as high as 0.5 with a D/A of ca. 20. The results implied that the photon energy captured by several donor molecules was collected by a single acceptor molecule (i.e. the harvesting of light energy). Enantioselectivity was observed, which indicates the participation of a contact pair of donor and acceptor molecules. For C₁₂-bpy and C₁₉-bpy, η_ET was low and exhibited no enantioselectivity, because their long alkyl chains inhibited close contact between the donor and acceptor molecules.