Excitation Dynamics and Relaxation in Molecular Aggregates and Photosynthetic Pigment-Protein Complexes

13:00 03-04-2014

Holon Institute of Technology, Faculty of Sciences

Excitation Dynamics and Relaxation in Molecular Aggregates and Photosynthetic Pigment-Protein Complexes
Professor Leonas Valkunas, Vilnius University

April 03, 2014 | 13:00 | Seminar Room 424/8

In photosynthesis the light-harvesting complexes are responsible for efficient excitation delivery to reactions centers responsible for conversion of the absorbed energy into the trans-membrane potential. This is the reason why the concept of photosynthetic antenna is widely used by describing the complete arrangement of the light-harvesting system. However, in plant photosynthesis the antenna plays an additional role – to control the excitation density in oxygen evolving PSII.
Indeed, this physiologically important strategy evolved by plants is responsible for a rapid regulation of excitation density at high light conditions known as the so-called non-photochemical quenching (NPQ) of excitations. Despite recent extensive discussions about the origin of the NPQ, a common agreement has not been achieved so far. The possible mechanisms caused by intermolecular resonance interaction between chlorophyll and carotenoid molecules and specificity of the excitation relaxation in the NPQ conditions will be considered.
A special attention will be paid to the possible role of coherence in the intermolecular interaction between chlorophylls and carotenoids. The role of coherence in excitation dynamics and its influence on the efficiency of energy transfer and photoinduced charge separation in molecular complexes is also intensively discussed during the last years.
This discussion originates from two-dimensional (2D) coherent electronic spectroscopy data, which recently demonstrated the oscillatory behavior in the 2D spectra of various molecular systems. However, it still remains unclear what is actually being observed: either excitonic and/or vibrational wavepacket motion.
The possibility to distinguish between the excitonic or vibrational origin of these oscillations will be demonstrated. The experiments obtained for some photosynthetic light-harvesting complexes, bacterial reaction centers and reactions centers of photosystem II (PSII) from plants will be analyzed.