The dependence of the ultrafast relaxation kinetics of the S-2 and S-1 states in beta-carotene homologs and lycopene on conjugation length studied by femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies

Kosumi, D., Fujiwara, M., Fujii, R., Cogdell, R.J., Hashimoto, H. and Yoshizawa, M. (2009) The dependence of the ultrafast relaxation kinetics of the S-2 and S-1 states in beta-carotene homologs and lycopene on conjugation length studied by femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies. Journal of Chemical Physics, 130(21), p. 214506. (doi:10.1063/1.3147008)

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Publisher's URL: http://dx.doi.org/10.1063/1.3147008

Abstract

The ultrafast relaxation kinetics of all-trans-beta-carotene homologs with varying numbers of conjugated double bonds n(n=7-15) and lycopene (n=11) has been investigated using femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies, both carried out under identical excitation conditions. The nonradiative relaxation rates of the optically allowed S-2(1(1)B(u)(+)) state were precisely determined by the time-resolved fluorescence. The kinetics of the optically forbidden S-1(2(1)A(g)(-)) state were observed by the time-resolved absorption measurements. The dependence of the S-1 relaxation rates upon the conjugation length is adequately described by application of the energy gap law. In contrast to this, the nonradiative relaxation rates of S-2 have a minimum at n=9 and show a reverse energy gap law dependence for values of n above 11. This anomalous behavior of the S-2 relaxation rates can be explained by the presence of an intermediate state (here called the S-x state) located between the S-2 and S-1 states at large values of n (such as n=11). The presence of such an intermediate state would then result in the following sequential relaxation pathway S-2 -> S-x -> S-1 -> S-0. A model based on conical intersections between the potential energy curves of these excited singlet states can readily explain the measured relationships between the decay rates and the energy gaps

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Cogdell, Professor Richard
Authors: Kosumi, D., Fujiwara, M., Fujii, R., Cogdell, R.J., Hashimoto, H., and Yoshizawa, M.
Subjects:Q Science > QD Chemistry
Q Science > QC Physics
College/School:College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:Journal of Chemical Physics
ISSN:0021-9606

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