Two-dimensional emission quenching and charge separation using a Ru(II)-photosensitizer assembled with membrane-bound acceptors

Novel syntheses of the bipyridine ligand 1, dcHb (dcHb = 4,4‘-dicarboxy-2,2‘-bipyridine), by anionic oxidation of 4,4‘-dimethyl-2‘,2-bipyridine (dmb) using molecular oxygen (4 atm), and of the sensitizer precursor 4, tris(4,4‘-diethoxycarbonyl-2,2‘-bipyridine)ruthenium(II) bis(triflate), from a chloride-free Ru(II) precursor 3b, RuII(DMSO)4(triflate)2-n(EtOH)n (n = 0−2, DMSO = dimethyl sulfoxide, triflate = OSO2CF3) are reported. The anionic sensitizer Ru(dcb)34- (5) was shown to bind to vesicles of lecithin when these were made positively charged by cationic bipyridinium electron acceptors. With cetylmethylviologen (CMV2+) as quencher, the time-resolved decay of the Ru(dcb)34- emission followed a model for diffusion-controlled quenching in two dimensions. However, the diffusion coefficient obtained from a fit to the data was very small, (6 ± 2) × 10-11 m2 s-1, comparable to values for amphiphiles in bilayers, even though Ru(dcb)34- diffuses in the water region at the vesicle surface. The quantum yield of...