The syntheses of several surfactant analogues of tris(2,2'-bipyridine)rutheni~m(iI)~+ is described together with a study of their photochemistry in spread films, monolayer assemblies, and at a monolayer assembly-water interface. It has been found that highly purified samples of the dioctadecyl ester of (4,4'-dicarboxy-2,2'-bipyridine)bis(2,2'-bipyridine)ruthenium( 11)2+ are inactive as catalysts for the photocleavage of water in monolayer assemblies. This is contrary to our previous findings, which employed a sample of the surfactant complex which has now been shown to contain several impurities, including other surfactant ruthenium(i1) complexes. The properties of films and monolayer assemblies of these complexes are found to be quite sample sensitive even when different samples of high indicated purity are employed. The failure of the highly purified complex to serve as a catalyst appears partially due to a light-induced destruction of assemblies irradiated in contact with water, which is due at least in part to a photohydrolysis of the ester group.The photochemistry of the tris(2,2'-bipyridine)ruthenium(I1) dication (Ru(bpy)32+) and related metal complexes has been the subject of considerable recent i n v e~t i g a t i o n .~-~~ It has been found that the excited states of Ru(bpy)32+ and other complexes having relatively long excited state lifetimes can be quenched by energy transfer, complex formation, and electron transfer processes. The latter have been observed both for cases where the excited state of Ru(bpy)32+ serves as an electron d~n o r~-~ as well as for instances where it acts as an electron acceptor.8-'0 There has been intense interest in the possibility that light driven electron transfer reactions can serve as useful energy conversion and storage processes,20-2' since the initial products of electron transfer are usually highly energetic, but stable, when isolated, molecules. In solution the high-energy products are rapidly degraded through reverse electron transfer with each other to form ground-state starting material^.^.^ Recently, interest has developed in the possibility of inhibiting these back reactions by various techniques, including the initiation of competitive processes or the carrying out of the reactions in other media.11,21 I n recent investigations, we have examined the photochemical reactivity of a number of chromophores in organized monolayer a~s e m b l i e s . l .~,~~-*~ In several cases it has been found that the controlled and highly condensed environment provided by the assemblies can strongly modify photoreactivity and luminescence behavior from that observed in solution. Our interest in light driven electron transfer processes involving Ru(bpy)32+ led us to prepare surfactant complexes of ruthenium( 11) for incorporation into monolayer assemblies. In a recent communication2 we reported that the strong luminescence of a surfactant ruthenium complex could be quenched by immersion of assemblies containing the complex into water. Concomitantly, the light-induced cleavage of w...

No abstract

No abstract

No abstract

No abstract