Configurations of Retinal and β-Carotene in the Lowest-Excited Triplet-State Produced from Different cis-trans Isomers

The triplet-state of retinal isomers was produced by direct flash-photolysis in hexane at room temperature, its transient Raman and transient absorption were recorded, and the products of photoisomerization were analyzed by HPLC. The results indicated (1) the all- trans , 7- cis , 9- cis and 11- cis isomers produce an "all- txans -like" triplet (which means it relaxes into the all- trans isomer) and (2) the 13- cis isomer produces a "13- cis -like" triplet in addition to the major "all- trans -like" triplet. \n The triplet-state of β-carotene isomers was produced by flash-photolysis using anthracene as a sensitizer at room temperature, its transient Raman was recorded, and the isomerization products were analyzed by HPLC. The results indicated (1) the all- trans and the 15- cis isomers produce only an "all- trans -like" triplet, (2) the 9- cis and the 13- cis isomers also produce the "all- trans -like" triplet as the major component, and (3) the 9- cis isomer produces additionally a "9- cis -like" triplet as the minor component.