Analysis of the photodecomposition products of Ru(bpy)3(2+) in various buffers and upon zeolite encapsulation

The photodecomposition products of Ru(bpy)3(2+) in water, in aqueous buffered solutions and encapsulated in zeolite-Y have been analyzed by chromatography and UV-visible spectroscopy. The chromatographic method is found to be capable of separating species with the same charge but slightly different ligands as well as geometrical isomers. In all the systems investigated, photodecomposition proceeded via photoaquation resulting in the formation of cis- and trans-Ru(bpy)2(OH2)2(2+). In the case of acetate and phthalate buffers, a third species, Ru(bpy)2(L)(OH2)+, where L is the buffer anion, was found to be the dominant product. For a given pH, the extent of decomposition was found to be dependent on both the buffer anion, following the trend, phosphate < acetate << phthalate and buffer concentration. The presence of the electron-transfer quenching agent, N,N'-dimethyl-4,4'-bipyridinium ion in the medium led to a decrease of the photodecomposition and closely followed the quenching efficiency as measured by intensity and lifetime quenching studies. Encapsulation of Ru(bpy)3(2+) in the supercages of zeolite-Y did not lead to a substantial decrease in photodecomposition as compared to an aqueous solution, suggesting that the expected enhanced stability of Ru(bpy)3(2+*) due to the destabilization of 3dd orbitals and the cage effect was being negated by the close proximity and intrazeolite packing of H2O molecules around the Ru center.