Photoinduced Electron Transfer in Ruthenium(II)−Rhodium(III) Terpyridine Dyads

• Published in: Inorganic chemistry 1997-09, Vol.36 (19), p.4247-4250
• Main Authors: Indelli, M. T, Scandola, F, Flamigni, L, Collin, J.-P, Sauvage, J.-P, Sour, A
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic9702577

A series of Ru(II)−Rh(III) dyads of general formula (ttpy)Ru−tpy−(ph) n −tpy−Rh(ttpy)5+ with n = 0, 1, 2 [ttpy = 4‘-p-tolyl-2,2‘:6,2‘‘-terpyridine; tpy−(ph) n −tpy = bridging ligand where two 2,2‘:6‘,2‘‘-terpyridine units are connected at the 4‘-position through a variable number of p-phenylene spacers] have been studied, in acetonitrile at room temperature, by picosecond and nanosecond time-resolved emission spectroscopy. When n = 1, excitation of the Ru(II)-based molecular component is followed by efficient intramolecular quenching by electron transfer to the Rh(III) center. The rate constant, k ≥ 3 × 109 s-1, is high despite the relatively small driving force of the process (ca. 0.1 eV). When n = 2, with the same driving force as above, no intramolecular electron transfer quenching is observed (upper limit for the rate constant of the electron transfer process:  k < 5 × 108 s-1). The decrease in electron transfer rate obtained in going from n = 1 to n = 2 is in line with the behavior of other systems containing poly-p-phenylene spacers. The dyad with n = 0 is definitely not homogeneous with the other two:  the intercomponent electronic coupling is much stronger, the Ru(II)-based excited state is lower in energy, and the electron transfer has a smaller driving force (ΔG ≈ 0). The lifetime of the Ru(II)-based emission is 17 ns. The lack of an obvious model compound makes it difficult to draw firm conclusions for this system.