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Temperature-induced switching of the mechanism for intramolecular energy transfer in a 2,2′:6′,2″-terpyridine-based Ru(II)-Os(II) trinuclear array

Lookup NU author(s): Professor Andrew Benniston, Emeritus Professor Anthony Harriman, Dr Peiyi Li, Craig Sams

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Abstract

The synthesis and photophysical properties of a linear 2,2′:6′, 2″-terpyridine-based trinuclear Ru-(II)-Os(II) nanometer-sized array are described. This array comprises two bis(2,2′:6′,2″- terpyridine) ruthenium(II) terminals connected via alkoxy-strapped 4,4′-diethynylated biphenylene units to a central bis-(2,2′: 6′,2″-terpyridine) osmium(II) core. The mixed-metal linear array was prepared using the "synthesis at metal" approach, and the Ru(II)-Ru(II) separation is ca. 50 Å. Energy transfer occurs with high efficiency from the Ru(II) units to the Os(II) center at all temperatures. Förster-type energy transfer prevails in a glassy matrix at very low temperature, but this is augmented by Dexter-type electron exchange at higher temperatures. This latter process, which is weakly activated, involves long-range superexchange interactions between the metal centers. In fluid solution, a strongly activated process provides for fast energy transfer. Here, a charge-transfer (CT) state localized on the bridge is populated as an intermediate species. The CT triplet does not undergo direct charge recombination to form the ground state but transfers energy, possibly via a second CT state, to the Os(II)-based acceptor. The short tethering strap constrains the geometry of the linker, especially in a glassy matrix, such that low-temperature electron exchange occurs across a particular torsion angle of 37°. The probability of triplet energy transfer depends on temperature but always exceeds 75%. © 2005 American Chemical Society.

Publication metadata

Author(s): Benniston AC, Harriman A, Li P, Sams CA

Publication type: Article

Publication status: Published

Journal: Journal of the American Chemical Society

Year: 2005

Volume: 127

Issue: 8

Pages: 2553-2564

ISSN (print): 0002-7863

ISSN (electronic): 1943-2984

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/ja044097r

DOI: 10.1021/ja044097r

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