Two-Dimensional Emission Quenching and Charge Separation Using a Ru(II)-Photosensitizer Assembled with Membrane-Bound Acceptors

• Published in: The journal of physical chemistry. B Vol. 101; no. 38; pp. 7494 - 7504
• Main Authors: Hammarström, Leif, Norrby, Thomas, Stenhagen, Gunnar, Mårtensson, Jerker, Åkermark, Björn, Almgren, Mats
• Format: Journal Article
• Language: English
• Published: American Chemical Society 18.09.1997
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp9710805

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)3 4- (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)3 4- 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)3 4- diffuses in the water region at the vesicle surface. The quantum yield of primary charge separation was 0.06 ± 0.02, which is significant, if not high, despite the large elecrostatic attraction between the reactants. Attempts were made to increase the charge separation yield by the use of a monocationic acceptor. Possible extensions of the system are discussed, such as charge separation across the vesicle membrane and the covalent linking of a donor to the sensitizer.