A first detection of singlet to triplet conversion from the 11B-u to the 13Ag state and triplet internal conversion from the 13Ag to the 13Bu state in carotenoids:: dependence on the conjugation length

Subpicosecond time-resolved absorption spectra were recorded in the visible region for a set of photosynthetic carotenoids having different numbers of conjugated double bonds (n), which include neurosporene (n = 9), spheroidene (n = 10), lycopene (n = 11), anhydrorhodovibrin (n = 12) and spirilloxanthin (n = 13). Singular-value decomposition and global fitting of the spectral-data matrices lead us to a branched relaxation scheme including both (1) the singlet internal conversion in the sequence of 1(1)B(u)(+) --> 1(1)B(u)(-) --> 2(1)A(g)(-) --> 1(1)A(g)(-) (ground), and (2) the singlet-to-triplet conversion of 1(1)B(u)(-) --> 1(3)A(g) followed by triplet internal conversion of l(3)Ag --> 1(3)B(u). (C) 2003 Elsevier B.V. All rights reserved.