SPECTROELECTROCHEMISTRY OF CAROTENOIDS IN SOLUTION

The D0 --> D2 Optical absorption spectra of the cation radicals of bet a-carotene and canthaxanthin in solution prepared using in situ spectr oelectrochemical techniques at 300 K are reported. The weak and usuall y not reported D0 --> D1 transition of the cation radicals of the caro tenoids are also observed in the optical spectra. The upper limit of t he apparent molar extinction coefficient of carotenoid dications in so lution is estimated to be on the order of 10(3) to 10(4). Under equili brium conditions, the contribution of the dication absorption spectrum to that of the cation radical spectrum is negligible for the canthaxa nthin cation radical and estimated to be approximately 10% for beta-ca rotene.