RESONANCE RAMAN-STUDY OF CAROTENOID CATION RADICALS

The resonance Raman (RR) spectra of the neutral and the cation radical of 8'-apo-beta-caroten-8'-al (I), 7',7'-dicyano-7'-apo-beta-carotene (II) and canthaxanthin (III) were measured using 752.6 nm laser excita tion. Optical and RR spectra of the electrochemically prepared cation radicals of I-III were measured in situ at different time intervals du ring the electrolysis. The RR spectra of the cation radicals are consi derably different from those of the neutral species. The frequencies o f the C=C stretching vibrations are decreased by 30-40 cm(-1), whereas those of C-C stretching vibrations are increased by 15-30 cm(-1). The se results suggest delocalization of the unpaired electron density thr oughout the entire carbon backbone which is consistent with our previo us EPR and ENDOR results.