We are a bunch of physical chemists/chemical physicists interested in studying the femtosecond to picosecond dynamics of complex chemical, biological and physical systems. To understand the ultrafast dynamics of complex systems with multiple states & transitions coupled to a messy environment, the method of choice is Ultrafast Coherent Multidimensional Optical Spectroscopy. In particular, our main tool is Two‐dimensional electronic spectroscopy (2DES). One can also consider 2DES as an "upgrade" of the conventional femtosecond visible transient absorption (TA) spectroscopy; 2DES unfolds the TA spectra onto two frequency (or wavelength) dimensions correlating excitation (pump) and detection (probe) frequencies at an experimental "pump-probe" delay time 2DES spectrum allows us to measure time and frequency resoleved dynamics.

Ultrafast Excitation Energy Transfer Pathways in Photosynthetic Systems

Photosynthesis is perhaps the most important biochemical process on earth as it ultimately fuels almost all life and bio-activity. It impacts important aspects of mankind, from food and energy security to environmental protection and climate change. There is also much interest in possible applications in artificial photosynthesis and bionanomaterials. These reasons make the full understanding of photosynthesis important, from the physical nature of its solar energy absorption and energy transfer processes to the photochemical reactions that it drives. 

In nature, photosynthesis is performed by a vast many organisms, from bacteria, algae, to green plants. Photosystem II (PSII) is a major component and the first step of the photosynthesis machinery. The whole PSII supercomplex (PSII-SC) is a large system and consists of the PSII-core complex where the reaction center (RC) is located. Attached to the core-complex are usually peripheral light-harvesting antenna (LHA) complex subunits. In the Figure above is shown the structure of the PSII-SC of higher plants. Photosynthesis in PSII begins with the light-capturing by the LHA (for plants, they are LHCII complexes). Subsequently, intra-subunit excitation energy transfer (EET) processes on tens of femtoseconds to picoseconds proceed. These are followed by inter-subunit EET processes (tens to a hundred picoseconds) into the PSII RCs in the core complex, which then results in the charge separation and water splitting reaction, that provides nearly all the oxygen content in the biosphere. This complex EET process is in timescales of tens to hundreds of picoseconds and is extremely efficient, but at the same it is robust  

Our research goal is to measure the EET network involved in PSII, we use Ultrafast Two-Dimensional Electronic Spectroscopy technique, or 2DES. The lessons learned in natural photosynthesis can be applied to develop photoelectrochemical systems and other artificial, advanced solar utilization technologies, important in powering the renewable energy economy for future global growth and sustainability.

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References

1. "Inter-subunit Energy Transfer Processes in a Minimal Plant Photosystem II Supercomplex", Sci. Adv. 10 (8) eadh0911 (2024). 

2. "Ultrafast Excitation Energy Transfer Dynamics in the LHCII−CP29−CP24 Subdomain of Plant Photosystem II", J. Phys. Chem. Lett. 13, 4263-4271 (2022). 

3. "Insights into the mechanisms and dynamics of energy transfer in plant light-harvesting complexes from two-dimensional electronic spectroscopy". Biochim. Biophys. Acta, Bioenerg. 1861 (4), 148050 (2020). 

4. "Direct observation of multistep energy transfer in LHCII with fifth-order 3D electronic spectroscopy", Nat. Comm. 6, 7194 (2015). 

5. "Pathways of energy transfer in LHCII revealed by room-temperature 2D electronic spectroscopy" Phys. Chem. Chem. Phys. 16, 11640-11646 (2014).