Studies on energy transfer from chiral polypyridyl Ru(II) to Os(II) complexes in cast and Langmuir-Blodgett films

Energy transfer from tris(4,7-diphenyl-1, 10-phenanthroline)ruthenium(II) p erchlorate (denoted by Ru(II)) to tris(4,7-diphenyl-1, 10-phenanthroline)os mium(II) perchlorate (denoted by Os(II)) has been studied in cast and Langm uir-Blodgett (LB) films. The work is focused on the packing effects of chir al metal complexes on energy-transfer rates. Three kinds of films were prep ared: a cast film of a 100:1 mixture of Lambda -Ru(II) and Lambda -Os(II) ( or Delta -Os(II)) (sample 1), a Y-type LB film of a 100:1 mixture of Lambda -Ru(II) and Lambda -Os(EI) (or Delta -Os(II)) (sample 2), and an alternati ve Y-type LB film of Lambda -Ru(II) and Lambda -Os(II) (or Delta -Os(II)) m onolayers (sample 3). In all of these samples, stearic acid (SA) is added a t a molecular ratio of [SA]/[Ru(II)] = 3 to stabilize a monolayer state. Fr om the analyses of the decay curves of excited Os(II) (denoted by Os(II)*), the apparent unimolecular energy-transfer rate constant from excited Ru(II ) (denoted by Ru(II)*) to Os(II), k(2), is determined. As a result, k(2) is found to. be larger for Lambda -Ru(II)*/Delta -Os(II) than for Lambda -Ru( II)*/Lambda -Os(II) in samples 1 and 3, while k(2) is larger for Lambda -Ru (II)*/Lambda -Os(II) than Lambda -Ru(II)*/-Os(II) in sample 2. The results are rationalized in term of the assumption that closer accessibility is att ained for the packing of the pseudo-racemic pair of Lambda -Ru(II)/Delta -O s(II) than for that of the pseudo-enantiomeric pair of Lambda -Ru(II)/Lambd a -Os(II), when one complex is located above the other, while the situation is reversed when one molecule is located by the side of the other.