ENDOR study of the (7′,7′-dicyano)- and (7′-phenyl)-7′-apo-β-carotene radical cations formed by UV photolysis of carotenoids adsorbed on silica gel

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Abstract
The radical cations of two synthetic carotenoids, 7′-7′-dicyano-7′-apo-β-carotene (I) and 7′-phenyl-7′-apo-β-carotene (II), have been prepared by UV irradiation of samples adsorbed on silica gel. The methyl proton hyperfine coupling constants were deduced from ENDOR powder spectra and assigned by RHF-INDO/SP calculations. The powder EPR spectra of the carotenoid radical cations formed photolytically by electron transfer are unresolved, with a peak-to-peak linewidth of 15 ± 1 G, irrespective of the donor or acceptor character of the terminal substituents.