Charge separation in donor-chromophore-acceptor assemblies. Linkage and driving force dependence of photoinduced electron transfers
- Colorado State Univ., Fort Collins, CO (United States)
A series of covalently linked Ru(bipyridine){sub 3}-donor-acceptor complexes was prepared where the donor-to-chromophore and acceptor-to-chromophore methylene chain lengths were varied. Time-resolved absorption studies were performed to elucidate intramolecular electron transfer rates. Oxidative quenching of the Ru(bipyridine){sub 3} metal-to-ligand charge transfer (MLCT) state followed by phenothiazine-to-ruthenium electron transfer resulted in a long-lived charge-separated state. A wavelength-dependent excitation resulted in a slowly decaying absorption which is assigned to the excited-state phenothiazine. The magnitude of this component in the transient absorption serves as an internal standard for determining relative quantum yield for formation of the charge-separated state. Marcus inverted region behavior was observed in back electron transfer. Rate constants for electron transfer from phenothiazine to Ru(III) decreased as the length of the bridging chain increased from p = 4 to 8. Chain length independence of the back electron transfer rate in the series of complexes with varied chromophore-acceptor distances (m = 2, 3, and 4) suggests the formation of an association complex during oxidative quenching of MLCT state and argues against a {delta}-bond superexchange pathway for back electron transfer. 16 refs., 3 figs., 3 tabs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG02-92ER14301
- OSTI ID:
- 50497
- Journal Information:
- Journal of Physical Chemistry, Vol. 99, Issue 17; Other Information: PBD: 27 Apr 1995
- Country of Publication:
- United States
- Language:
- English
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