Conjugation length dependence of internal conversion in carotenoids: role of the intermediate state.
We report on a sub-20-fs transient absorption study of the S2(1(1)B(+)(u))-->S1(2(1)A(-)(g)) internal conversion in a series of carotenoids with a number of conjugated double bonds (N) ranging from 5 to 15. For the longer carotenoids (N>or=9), the measurements reveal the existence of an additional intermediate excited state lying between the optically allowed S2 state and the lower-lying forbidden S1 state. This state enables us to explain the nonmonotonic dependence of the S2-->S1 conversion rate on N and is expected to play an important role in photosynthetic light harvesting.
Polli
D
D
ULTRAS-INFM, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan, Italy.
Cerullo
G
G
Lanzani
G
G
De Silvestri
S
S
Yanagi
K
K
Hashimoto
H
H
Cogdell
R J
RJ
D002338:Carotenoids / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D013329:Structure-Activity Relationship
D002338:Carotenoids; C008604:neurosporene