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

Energy transfer was investigated between two types of iridium(III) complexes, [Ir(dfppy)2(Cn-bpy)](+) (dfppyH = 2-(2',4'-difluorophenyl)pyridine; Cn-bpy = 4,4'-dialkyl-2,2'-bipyridine; dialkyl = dimethyl (C1), didodecyl (C12), and dinonyldecyl (C19)) and [Ir(piq)2(Cn-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.