Singlet-Oxygen Quenching by Carotenoids: Steady-state luminescence experiments

The near-infrared luminescence of singlet oxygen (¹O₂) has been measured in order to determine the efficiency of ¹O₂ quenching by two carotenoid compounds, β-carotene and canthaxanthin. 1H-Phenalen-1-one and rose bengal have been used as photosensitizers in those steady-state luminescence experiments. Stern-Volmer analysis of the ¹O₂ luminescence in solutions of CCl₄ and CD₃OD, containing different concentrations of the carotenoids, has shown a very efficient quenching by canthaxanthin. The rate constants are about a factor of 2 below the diffusion limited values for the given solvents, confirming earlier results in benzene. In comparison, the efficiency of ¹O₂ quenching by β-carotene is slightly lower than that by canthaxanthin in non-polar solvents and is reduced by an order of magnitude in CD₃OD, due to the aggregation of this quencher.