Photoinduced Electron Transfer between a Carotenoid and TiO2 Nanoparticle
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- 作者：Jie Pan ; Gá ; bor Benkö ; Yunhua Xu ; Torbjö ; rn Pascher ; Licheng Sun ; Villy Sundströ ; m ; and Tomá ;
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- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：November 20, 2002
- 年：2002
- 卷：124
- 期：46
- 页码：13949 - 13957
- 全文大小：155K
- 年卷期：v.124,no.46(November 20, 2002)
- ISSN：1520-5126
文摘
The dynamics of photoinduced electron injection and recombination between all-trans-8'-apo-
-caroten-8'-oic acid (ACOA) and a TiO2 colloidal nanoparticle have been studied by means of transientabsorption spectroscopy. We observed an ultrafast (~360 fs) electron injection from the initially excited S2state of ACOA into the TiO2 conduction band with a quantum yield of ~40%. As a result, the ACOA
+radical cation was formed, as demonstrated by its intense absorption band centered at 840 nm. Becauseof the competing S2-S1 internal conversion, ~60% of the S2-state population relaxes to the S1 state. Althoughthe S1 state is thermodynamically favorable to donate electrons to the TiO2, no evidence was found forelectron injection from the ACOA S1 state, most likely as a result of a complicated electronic nature of theS1 state, which decays with a ~18 ps time constant to the ground state. The charge recombination betweenthe injected electrons and the ACOA+ was found to be a highly nonexponential process extending frompicoseconds to microseconds. Besides the usual pathway of charge recombination forming the ACOAground state, about half of the ACOA+ recombines via the ACOA triplet state, which was monitored by itsabsorption 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 ~7.3 
s. By examination of theprocess of photoinduced electron transfer in a carotenoid-semiconductor system, the results provide aninsight into the photophysical properties of carotenoids, as well as evidence that the interfacial electroninjection occurs from the initially populated excited state prior to electronic and nuclear relaxation of thecarotenoid molecule.
-caroten-8'-oic acid (ACOA) and a TiO2 colloidal nanoparticle have been studied by means of transientabsorption spectroscopy. We observed an ultrafast (~360 fs) electron injection from the initially excited S2state of ACOA into the TiO2 conduction band with a quantum yield of ~40%. As a result, the ACOA+radical cation was formed, as demonstrated by its intense absorption band centered at 840 nm. Becauseof the competing S2-S1 internal conversion, ~60% of the S2-state population relaxes to the S1 state. Althoughthe S1 state is thermodynamically favorable to donate electrons to the TiO2, no evidence was found forelectron injection from the ACOA S1 state, most likely as a result of a complicated electronic nature of theS1 state, which decays with a ~18 ps time constant to the ground state. The charge recombination betweenthe injected electrons and the ACOA+ was found to be a highly nonexponential process extending frompicoseconds to microseconds. Besides the usual pathway of charge recombination forming the ACOAground state, about half of the ACOA+ recombines via the ACOA triplet state, which was monitored by itsabsorption 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 ~7.3 s. By examination of theprocess of photoinduced electron transfer in a carotenoid-semiconductor system, the results provide aninsight into the photophysical properties of carotenoids, as well as evidence that the interfacial electroninjection occurs from the initially populated excited state prior to electronic and nuclear relaxation of thecarotenoid molecule.