Energy transfer in light-harvesting antennae studied by nonlinear spectroscopic techniques

Abstract

Two non-linear spectroscopic techniques, high-intensity pump-probe and three-pulse photon echo, have been used to investigate the energy transfer and excitation dynamics in various light-harvesting antennae from plants and purple bacteria. At high excitation intensities, excitation annihilation, the process that is (at least partly) governed by energy transfer, takes place. It can be monitored using time-resolved difference absorption spectroscopy; the information about energy transfer process can be devised from the time evolution of the spectra. We modeled the experimental data using multi-particle Monte-Carlo model for excitation annihilation. This model was based on the known structural information on the investigated antenna complexes and allowed to explain qualitatively the time-dependence of pump-probe spectra and estimate energy transfer parameters (transfer rates between different pigments) in investigated light-harvesting complexes. Three-pulse photon echo is another technique that allows monitoring, among others, the energy transfer process. The three-pulse echo peak shift experiments were performed on the same type of systems, as investigated by pump-probe spectroscopy. The results revealed by both methods were compared. The applicability of the methods was evaluated and the excitation energy transfer dynamics was established in several light-harvesting antennae.