An intramolecular charge transfer state of carbonyl carotenoids: implications for excited state dynamics of apo-carotenals and retinal

Excited state dynamics of two apo-carotenals, retinal and 12'-apo-β-carotenal, were studied by femtosecond transient absorption spectroscopy. We make use of previous knowledge gathered from studies of various carbonyl carotenoids and suggest that to consistently explain the excited-state dynami...

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Published in:Physical chemistry chemical physics : PCCP 2011-01, Vol.13 (22), p.10787-10796
Main Authors: Polívka, Tomáš, Kaligotla, Shanti, Chábera, Pavel, Frank, Harry A
Format: Article
Language:English
Subjects:
Carbonyls
Carotenoids
Carotenoids - chemistry
Decay
Dynamics
Excitation
Hexanes - chemistry
Methanol - chemistry
Methyl alcohol
Retinaldehyde - chemistry
Silver
Solvents
Time Factors
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Summary:Excited state dynamics of two apo-carotenals, retinal and 12'-apo-β-carotenal, were studied by femtosecond transient absorption spectroscopy. We make use of previous knowledge gathered from studies of various carbonyl carotenoids and suggest that to consistently explain the excited-state dynamics of retinal in polar solvents, it is necessary to include an intermolecular charge transfer (ICT) state in the excited state manifold. Coupling of the ICT state to the A(g)(-) state, which occurs in polar solvents, shortens lifetime of the lowest excited state of 12'-apo-β-carotenal from 180 ps in n-hexane to 7.1 ps in methanol. Comparison with a reference molecule lacking the conjugated carbonyl group, 12'-apo-β-carotene, demonstrates the importance of the carbonyl group; no polarity-induced lifetime change is observed and 12'-apo-β-carotene decays to the ground state in 220 ps regardless of solvent polarity. For retinal, we have confirmed the well-known three-state relaxation scheme in n-hexane. Population of the B(u)(+) state decays in
ISSN:1463-9076
1463-9084
DOI:10.1039/c1cp20269c