J. Phys. Chem. 1988, 92, 2101-2108
2101
ARTICLES Time-Resolved Resonance Raman Spectroscopy of Triplet @-CaroteneProduced from Ail-Trans, ir-cis, 9-Cis, 13-Cis, and 15-Cis Isomers and High-pressure Liquid Chromatography Analyses of Photoisomerization via the Triplet State' Hideki Hashimoto and Yasushi Koyama* Faculty of Science, Kwansei Gakuin University, Uegahara, Nishinomiya 662, Japan (Received: June 1, 1987; In Final Form: October 20, 1987)
Time-resolved resonance Raman spectra of the triplet state, which was produced by anthracene-sensitized flash photolysis of the all-trans, 7 4 , 9 4 s , 1 3 4 , and 1 5 4 s isomers of p-carotene, were recorded. As for the initial and final ground-state configurations, excitation from and subsequent relaxation to the original isomer were seen in the case of the all-trans, 7-cis, and 9-cis isomers; on the other hand, excitation from the original isomer and subsequent isomerization into the all-trans isomer were seen in the case of the 13-cis and 15-cis isomers. At maximum triplet population, the all-trans and the 15-cis isomers showed an identical spectrum, but other isomers showed similar but different spectra of their own. The analyses by high-pressure liquid chromatography (HPLC) of anthracene-sensitizedphotoisomerization for the above isomers confirmed the above observation o! isomerization by Raman spectroscopy. The relative quantum yield of isomerization was in the order all-trans < 7-cis < 9-cis
