P. Andersson, T. Gillbro
Aug 15, 1995
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Journal
Journal of Chemical Physics
Abstract
In this paper we explore the intramolecular relaxation processes within two long carotenoids, namely decapreno‐β‐carotene (M15) and dodecapreno‐β‐carotene (M19) with 15 and 19 conjugated double bonds (N), respectively. Amplified 200 fs pulses at 590 nm were used to excite the optically allowed S0→S2 (1 1Ag→1 1Bu) transition of the two carotenoids. The excited state dynamics were probed by continuum light between 400–890 nm in solvents with different polarizabilities. The transient absorption spectra consist of a bleaching region, due to loss of ground state absorption, and of an excited state absorption region at longer wavelengths, due to the S1→Sn transition. The Sn state was assigned to an n 1Bu state. The overall wavelength dependence of the measured kinetics could be well described by introducing three decay time constants. One reflects the S1 lifetime (τ1) and was determined to 1.1 and 0.5 ps for M15 and M19, respectively. A second lifetime, between 5 and 15 ps, was attributed to vibrational cooling...