Pure and Applied Chemistry

Abstract: The fundamental interactions between naturally occurring pigments in light-harvesting systems are responsible for the high efficiency of the photosynthetic apparatus. We describe the role of carotenoids (Cars) in light-harvesting systems, including our work elucidating the mechanism of energy transfer from the optically dark Car singlet excited state (S₁) to chlorophyll (Chl) and calculations on the electronic structure of Cars by means of time-dependent density functional theory (TDDFT). We highlight new studies on the charge-transfer state of the Car, peridinin (Per), which enhances the light-harvesting efficiency of the Car by increasing the electronic coupling to Chl. The role of another Car, zeaxanthin (Zea), is discussed with respect to its role in the mechanism of the feedback deexcitation quenching in green plants, a vital regulation process under light conditions which exceed photosynthetic capacity. Lastly, we provide insight on how the 96 Chls in Photosystem I are optimized to generate a pigment-protein complex which utilizes solar energy with near unit efficiency.