Conjugation-Length Dependence of the T₁ Lifetimes of Carotenoids Free in Solution and Incorporated into the LH2, LH1, RC and RC-LH1 Complexes: Possible Mechanisms of Triplet-Energy Dissipation

Abstract

The triplet-state absorption spectra were recorded for carotenoids (Cars), whose number of conjugated double bonds (n) being in the region of 9–13, to determine the dependence on n of the T₁ lifetimes (τ), and reached to the following conclusions: (1) A substantial shift of the linear dependence to shorter lifetimes, on going from solution to the LH2 complex, was ascribed to the twisting of the Car conjugated chain. (2) A substantial decrease in the slope of the linear dependence, on going from the reconstituted LH1 to the LH1 component of the RC-LH1 complex, was ascribed to the minor-component Car forming a leak channel of triplet energy. (3) The loss of conjugation length-dependence, on going from the isolated RC to the RC component of the RC-LH1 complex, was ascribed to a triplet-energy reservoir consisting of bacteriochlorophylls in the RC component.