Energy Transfer in Monolayer Assemblies of Surfactant Ruthenium Complexes

Abstract

Energy transfer in monolayer assemblies has been studied with bis(2,2'-bipyridyl)(dioctadecyl 2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) perchlorate (1) as acceptor and bis(2,2'-bipyridyl)- (4,4'-dieicosyl-2,2'-bipyridyl)ruthenium(II) perchlorate (2), bis(2,2'-bipyridyl)(4-eicosyl-4'-methyl- 2,2'-bipyridyl)ruthenium(II) perchlorate (3), or bis(o-phenanthroline)(4,4'-dioctadecyl-2,2'-bipyridyl)- ruthenium(II) (4) as donor. Forster theory was used to analyse transfer rate constants, obtained by measuring the reduction in intensity of the donor luminescence in the presence of acceptors. This luminescence quenching involves energy transfer and not electron transfer because of the sensitized luminescence intensity of the acceptor. The efficiency of energy transfer depends on the relative orientations of the alkyl chains. The observed rates of transfer greatly exceed the efficiency predicted from the Forster theory for the distance between the chromophores; it is suggested that the alkyl chains take part in the transfer of excitation energy. This effect can be largely suppressed by the insertion of a 'spacer' monolayer of cadmium arachidate between donor and acceptor layers.