Energy Transfer between Ru(II) and Os(II) Polypyridyl Complexes Linked to Polystyrene

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2002-03, Vol.106 (10), p.2328-2334
• Main Authors: Fleming, Cavan N, Dupray, Laurence M, Papanikolas, John M, Meyer, Thomas J
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp012990w

Energy transfer between RuII and OsII polypyridyl complexes covalently attached to polystyrene has been in studied in CH3CN. The polymer is a 1:1 styrene-p-aminomethylstyrene copolymer derivatized by amide coupling with the acid-functionalized metal complexes [MII(bpy)2(bpy-COOH)](PF6)2 (MII = RuII, OsII; bpy is 2,2‘-bipyridine and bpy-COOH is 4‘-methyl-2,2‘-bipyridine-4-carboxylic acid). In the resulting polymer [co-PS−CH2NHCO−(RuII 11OsII 5)](PF6)32, 11 of, on the average, 16 polymer sites are derivatized by RuII and five by OsII. Photophysical properties compared to the homopolymers [co-PS−CH2NHCO−(RuII 16)](PF6)32 and [co-PS−CH2NHCO−(OsII 16)](PF6)32 reveal that excitation at RuII is followed by efficient energy transfer to the lower energy OsII sites with near unit efficiency (95%). Time-correlated single photon counting measurements with picosecond time resolution reveal that quenching of RuII* produced adjacent to an OsII trap site is quenched with an average rate constant 〈k en 〉 = 4.2 × 108 s-1. RuII* decay and OsII* sensitization kinetics are complex because the polymer sample consists of a distribution of individual strands varying in chain length, loading pattern, and number of styryl spacers. The kinetics are further complicated by a contribution from random walk energy migration. An average energy transfer matrix element of 〈V en 〉 ∼ 2 cm-1 for RuII* → OsII energy transfer has been estimated by using emission spectral fitting parameters to calculate the energy transfer barrier.