PHOTOSENSITIZATION OF COLLOIDAL SNO2 IN AN ASYMMETRIC SUPPORTED BILAYER COMPOSED OF 2 TYPES OF SURFACTANTS

Surfactant bilayers composed of a cationic surfactant, didodecyldimethylammonium ion (DDMA(+)), and a zwitterionic one, 1,2-dioctanoyl-sn-glycero-1-phosphocholine, deposit onto negatively charged colloidal (ca. 4 nm diameter) SnO2 particles such that the DDMA(+) molecules are predominantly located in the inner monolayer, i.e., serving as counterions to the particle surface charges. The asymmetric configuration of the constituents of the bilayer is revealed by the photophysical properties of an amphiphilic ruthenium(II) polypyridine complex, Ru(bpy)(2)L(2+) (bpy = 2,2'-bipyridine, L = 5-hexadecamido-1,10-phenanthroline). The excited state of this photosensitizer, *Ru(bpy)(2)L(2+), is quenched to an extent of >95% via electron transfer to the SnO2 particle conduction band, indicating that almost all of the photosensitizer molecules are dissolved in the monolayer adjacent to the SnO2 surface. The conduction band electron produced via this reaction is shown to reduce 1,1'-di-n-hexadecyl-4,4'-bipyridinium ion, C16V2+, that is also incorporated into the supported bilayer, so that the net transfer of an electron from *Ru(bpy)(2)L(2+) to C16V2+ is mediated by the SnO2 particle. The overall efficiency for the reduction of C16V2+ by *Ru(bpy)(2)L(2+) is 0.3 +/- 0.1. The trapping of the conduction band electron by C16V2+ has the effect of lengthening the lifetime of Ru(bpy)(2)L(3+) by an order of magnitude over the lifetime observed without C16V2+.