ETUDE PAR SPECTROSCOPIE D'ECLAIRS DU TRANSFERT D'ENERGIE CHLOROPHYLLE-CAROTENOIDE

Abstract— Energy transfer from chlorophyll A in its lowest triplet state to carotenoid pigments is demonstrated by rapid flash photolysis experiments.
Two systems are used; the first consists of chlorophyll A and p carotene in organic solvents: in diluted solutions, energy transfer is diffusion controlled. The second consists of chlorophyll A and lutein incorporated into digitonin micelles suspended in water; with this system a very rapid energy transfer is observed (< 0.4 × 10^--⁶ sec).
Energy transfer results in a carotenoid metastable state, which is supposed to be a triplet state; for lutein its half-life is 8·9 × 10^--⁶ sec, and it has an absorption peak at 518 nm. Depopulation of lutein ground state, around 450 nm, can be observed, as well as the reactivity of oxygen towards the metastable state.
Most of these results were obtained with a Q -switch ruby laser as exciting source (6943 Å). A 4350 Å flash can also be obtained by two successive non linear effects. Using this flash for exciting chlorophyll A alone, a strong signal is detected, due to its triplet state. By exciting directly B carotene or lutein, it is not possible to detect any metastable state with our technique.