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- Ghanem, Raed, et al.
(författare)
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Light-driven tyrosine radical formation in a ruthenium-tyrosine complex attached to nanoparticle TiO2
- 2002
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 41:24, s. 6258-6266
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a possibility of multistep electron transfer in a supramolecular complex adsorbed on the surface of nanocrystalline TiO2. The complex mimics the function of the tyrosinez and chlorophyll unit P-680 in natural photosystem II (PSII). A ruthenium(II) tris(bipyridyl) complex covalently linked to a L-tyrosine ethyl ester through an amide bond was attached to the surface of nanocrystalline TiO2 via carboxylic acid groups linked to the bpy ligands. Synthesis and characterization of this complex are described. Excitation (450 nm) of the complex promotes an electron to a metal-to-ligand charge-transfer (MLCT) excited state, from which the electron is injected into TiO2. The photogeneration of Ru(III) is followed by an intramolecular electron transfer from tyrosine to Ru(III), regenerating the photosensitizer Ru(II) and forming the tyrosyl radical. The tyrosyl radical is formed in less than 5 us with a yield of 15%. This rather low yield is a result of a fast back electron transfer reaction from the nanocrystalline TiO2 to the photogenerated Ru(III).
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| 3. |
- Pan, Jie, et al.
(författare)
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Photoinduced electron transfer between a carotenoid and TiO2 nanoparticle
- 2002
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 124:46, s. 13949-13957
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of photoinduced electron injection and recombination between all-trans-8'-apo-beta-caroten-8'-oic acid (ACOA) and a TiO2 Colloidal nanoparticle have been studied by means of transient absorption spectroscopy. We observed an ultrafast (similar to360 fs) electron injection from the initially excited S-2 state of ACOA into the TiO2 conduction band with a quantum yield of similar to40%. As a result, the ACOA(.+) radical cation was formed, as demonstrated by its intense absorption band centered at 840 nm. Because of the competing S-2-S-1 internal conversion, similar to60% of the S-2-state population relaxes to the S-1 state. Although the S-1 state is thermodynamically favorable to donate electrons to the TiO2, no evidence was found for electron injection from the ACOA S, state, most likely as a result of a complicated electronic nature of the S, state, which decays with a similar to18 ps time constant to the ground state. The charge recombination between the injected electrons and the ACOA(.+) was found to be a highly nonexponential process extending from picoseconds to microseconds. Besides the usual pathway of charge recombination forming the ACOA ground state, about half of the ACOA(.+) recombines via the ACOA triplet state, which was monitored by its absorption band at 530 nm. This second channel of recombination proceeds on the nanosecond time scale, and the formed triplet state decays to the ground state with a lifetime of similar to7.3 mus. By examination of the process of photoinduced electron transfer in a carotenoid-semiconductor system, the results provide an insight into the photophysical properties of carotenoids, as well as evidence that the interfacial electron injection occurs from the initially populated excited state prior to electronic and nuclear relaxation of the carotenoid molecule.
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