THE PHOTOPHYSICS AND PHOTOCHEMISTRY OF THE CAROTENOIDS

Considerable interest has been shown in the carotenoids for many years due to their wide ranging roles in photochemistry, photobiology and photomedicine and their possible use as a chemopreventative treatment for cancer. Studies about 20 years ago identified the triplet-triplet absorption of β-carotene; this work was of importance in understanding the protective role of these molecules in photosynthesis and bacterial photosynthesis and in porphyric disease treatment. Recently, attention has turned to the very weak fluorescence of these systems using picosecond measurements; results are related to the antenna role of carotenoids in photosynthesis. Photoisomerization continues to be studied with many of the recent developments based on pump-probe measurements using time-resolved resonance Raman spectroscopy for monitoring both the triplet state and the forbidden (1Ag-*) excited singlet state. Interest is also currently centred on the interaction of singlet oxygen with carotenoids; these studies are of value in photophysics (e.g. determination of the carotenoid lowest triplet energy level) and in photomedicine (e.g. evaluation of the use of carotenoids as chemopreventative drugs). © 1990.