Triplet-sensitized and thermal isomerization of all-trans, 7-cis, 9-cis, 13-cis, and 15-cis isomers of. beta. -carotene: Configurational dependence of the quantum yield of isomerization via the T sub 1 state

Journal Article · Thu Sep 19 00:00:00 EDT 1991 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100172a016· OSTI ID:5225863

Kuki, Michitaka; Koyama, Yasushi ^[1]; Nagae, Hiroyoshi ^[2]

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1. Kwansei Gakuin Univ., Uegahara (Japan)
2. Kobe City Univ. of Foreign Studies (Japan)

The products of triplet-sensitized photoisomerization (excitation at 337 mn of the sensitizer, anthracene) and thermal isomerization of {beta}-carotene in {eta}-hexane, starting from the all-trans, 7-cis, 9-cis, 13-cis, and 15-cis isomers, were analyzed by HPLC. Direct photoisomerization (excitation at 488 and 337 mn) was also examined for comparison. Three different isomerization patterns were found in both triplet-sensitized and thermal isomerization: pattern A, cis to trans isomerization around each cis bond; pattern B, trans to cis isomerization in the central part of the conjugated chain; and pattern C, cis to another cis isomerization. In the T{sub 1} state, the pattern A isomerization was predominant even for the peripheral-cis (7-cis and 9-cis) isomers and its efficiency was extremely high for the central-cis (13-cis and 15-cis) isomers. In the S{sub 0} state, the pattern B isomerization, instead, was predominant for the peripheral-cis isomers, and the pattern A isomerization was predominant only for the central-cis isomers. The quantum yields of triplet-sensitized isomerization (decrease of the starting isomer per triplet species generated) were determined to be as follows: all-trans, 0.04; 7-cis, 0.12; 9-cis, 0.15; 13-cis, 0.87; and 15-cis, 0.98. Carbon-carbon {pi} bond orders of model polyenes in the T{sub 1} and S{sub 0} states were calculated by using the Pariser-Parr-Pople CI theory; bond lengths were optimized by using a bond order-bond length relationship. Isomerization characteristics in the T{sub 1} and S{sub 0} states observed were discussed based on the results of the calculations.

• OSTI ID: 5225863
• Journal Information: Journal of Physical Chemistry; (United States), Vol. 95:19; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CAROTENOIDS
ISOMERIZATION
CHEMICAL REACTION YIELD
EXPERIMENTAL DATA
LASER RADIATION
LIQUID COLUMN CHROMATOGRAPHY
MATHEMATICAL MODELS
MOLECULAR STRUCTURE
NUCLEAR MAGNETIC RESONANCE
PHOTOCHEMICAL REACTIONS
THEORETICAL DATA
THERMOCHEMICAL PROCESSES
ULTRAVIOLET RADIATION
VISIBLE RADIATION
CHEMICAL REACTIONS
CHROMATOGRAPHY
DATA
ELECTROMAGNETIC RADIATION
HYDROCARBONS
INFORMATION
MAGNETIC RESONANCE
NUMERICAL DATA
ORGANIC COMPOUNDS
PIGMENTS
RADIATIONS
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SEPARATION PROCESSES
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400201* - Chemical & Physicochemical Properties