LES CAROTENES FLUORESCENT‐ILS?*

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Abstract
Abstract— –Carotenoids, with II conjugated double bonds show a lack of fluorescence. For β‐carotene, no U.V. fluorescence (300–400 nm) is observed with a quantum yield greater than 10‐4 we have observed a large hand visible fluorescence, already described by several authors, but this fluorescence remains when the β‐carotene is bleached, and must be assigned to some impurity present with β‐carotene. The fluorescence of lycopene solutions, whose quantum yield should be smaller than 10‐3, is similarly assigned to an impurity less photosensitive than lycopene. The fluorescence of canthaxanthine is also very weak (quantum yield ˜ 2. 10‐5). In the deactivation paths to the ground state, photodecomposition is quite unimportant, and probably photoisomerisation too: internal conversion appears to be extremely rapid, within a time scale comparable with the periods of vibration of the carbon atoms.

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