Exciton migration and fluorescence quenching in LHCII aggregates: Target analysis using a simple nonlinear annihilation scheme

When exposed to excess light illumination photosynthetic organisms switch into a photoprotective quenched state where the excess energy is safely dissipated as heat. When these processes are investigated by means of ultrafast spectroscopy, the experimentalist is faced with the unnatural process of singlet–singlet annihilation which often makes the interpretation of the results very complicated. It was recently discovered that the main light-harvesting complex of plants, LHCII, plays a key role in the dissipation of excess energy in the process of non-photochemical quenching. Here we demonstrate that the excitation kinetics in the quenched state can be described by a simple model, which assumes specific trapping centers to be present in the system. In order to explain the experimental results a physical model for exciton–exciton annihilation is applied. Besides providing a more detailed interpretation of the kinetic data, the model provides a general annihilation scheme which can potentially be applied to a number of systems provided the pool of pigments is sufficiently large. 2008 Elsevier B.V. All rights reserved.