BETA-CAROTENE TRIPLET-STATE ABSORPTION IN THE NEAR-IR RANGE

The beta-carotene absorption from the lowest triplet state was investigated over a wide spectral range. A new absorption transition in the near-IR region was found. The absorption band exhibited a 0-0 transition at about 8100 cm(-1) with a low intensity, lower by a factor of approximately 300 than the intensity of the known triplet-triplet absorption in the visible range. The vibronic structure of the absorption band was similar to that of the steady state beta-carotene absorption. The energy of the triplet state, resulting from this near-IR transition, was close to the beta-carotene S-1 state energy. Correspondingly, the interconversion of the carotenoid should depend on the features of this triplet state. Moreover, this relatively low-lying triplet state could also take part in the quenching of molecular triplet states by carotenoids.