ON THE TRIPLET-TRIPLET ENERGY TRANSFER FROM CHLOROPHYLL TO CAROTENE IN TRITON X 100 MICELLES

Abstract— The kinetics of the triplet-triplet energy transfer of chlorophyll α (Cha) to β carotene (Car) has been investigated in Triton X100 micelles by 353 nm laser flash photolysis. This transfer consists of an intramicellar process involving pigment species located in the same micelle. A kinetic model using a bimolecular treatment leads to a rate constant of the energy transfer in the micellar phase ( k _tm≅ 6 × 10⁸ M ^-1 s^-1) lower than the previously determined values in homogeneous solvents ( k _t≅ 4.6 ≅ 10⁹ M ^-ls^-l); this result shows the high microviscosity of the micellar core. In addition, the apparent bimolecular rate constant ( k _t≅ 5.0 ≅ 10¹⁰ M ^-l s^-1) appears to be an order of magnitude higher than in homogeneous solvents. The lifetime of the carotene triplet state is the same in the hydrophobic core of Triton X100 micelles (τ a = 7.7 μs) as in organic solvents (hexane or carbon disulfide). The transfer yield is controlled by the distribution of chlorophyll and carotene molecules in the micelles.