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THE S 0 AND Ti STATES OF ISOMERIC CANTHAXANTHIN AS COMPARED WITH THOSE OF β‐CAROTENE: EFFECT OF THE TERMINAL CARBONYL GROUPS DETECTED BY RAMAN SPECTROSCOPY
Author(s) -
Hashimoto Hideki,
Koyama Yasushi
Publication year - 1991
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1991.tb01986.x
Subject(s) - canthaxanthin , chemistry , raman spectroscopy , double bond , conjugated system , photochemistry , excited state , carbon fibers , singlet state , stereochemistry , crystallography , carotenoid , organic chemistry , materials science , physics , polymer , astaxanthin , food science , composite number , nuclear physics , optics , composite material
The S 0 (ground singlet‐state) Raman spectra of the all‐trans, 9‐cis, 13‐cis, 9,9‐cis, 9, 13‐cis , 9,13′‐cis and 13,13′‐cis isomers of canthaxanthin as well as the T 1 (lowest‐excited triplet‐state) Raman spectra of the all‐trans, 9‐cis, 13‐cis and 9,13‐cis isomers were recorded. In order to reveal the effect of the carbonyl groups at both ends on the carbon‐carbon conjugated system in‐between (in both the S 0 and T, states), the carbon‐carbon stretching frequencies were compared between isomeric canthaxanthin and p‐carotene: in the S 0 state, the C=C stretching frequencies of canthaxanthin were lower by3–10 cm −1 than those of β‐carotene, indicating increased conjugation in the former. In the T, state, the “C=C” stretching frequencies of canthaxanthin were lower by12–15 cm −1 , indicating a large decrease in the “C=C” bond order in the central part of canthaxanthin. Further, the relations of the C=C (S 0 ) and “C=C” (T 1 ) stretching frequencies vs the number of carbon‐carbon double‐bonds were examined for the above two and additional five carotenoids. The result indicated that the terminal carbonyl groups of canthaxanthin are incorporated in the carbon‐carbon conjugated system in the T, state, but that they are almost independent of it in the S 0 state. Both observations support the idea that the “triplet‐excited region” of canthaxanthin is extended over the entire double‐bond system.