Polaron Dynamics in Two-dimensional Photon-echo Spectroscopy of Molecular Rings

摘要

Nonlinear femtosecond optical spectroscopy is one of the major sources of information on the functioning of photosynthetic systems1–3. With recent technological advances, the technique of two-dimensional (2D) electronic spectroscopy has emerged as a highly sophisticated tool for studying excitonic relaxation and dephasing in a variety of molecular and biological systems4–7. Coherent and incoherent exciton dynamics in H- or J-type aggregates and in light-harvesting complexes can be probed by various optical measurements such as time-resolved fluorescence, pump-probe, photon echoes, 2D electronic spectroscopy and 2D infrared spectroscopy. The availability of nonlinear optical responses has also enormously enriched our knowledge on the role of disorder in molecular transitions and the effects caused by multiexciton interactions. However, due to enormous complexity of photosynthetic systems, the interpretation of the results is still a huge challenge, and the validity of the exciton approach when subjected to the coupling to different types of baths ranging from water to proteins is contentious. Proper interpretation of measured signals and extraction of useful information out of them is virtually impossible without adequate theoretical support.