Energy and electron transfer reactions of polyenic acids with variable chain lengths

Highly unsaturated conjugated fatty acids (carotenoic acids) with 5–15 conjugated double bonds were irradiated by flash pulses in the presence of the sensitizer riboflavin. The resulting triplet and radical cation transients were analyzed and the underlying energy and electron transfer reactions determined experimentally and by calculation. The two key antioxidant reactions of carotenoids summarize in ar, the ratio of the reaction constants for electron and energy transfer. The optimal antioxidant ratio ar cumulated in the polyenic acid with 11 double bonds. The photophysical formation of radical cations was chemically ascertained by reaction of the acids with FeCl3.