Delocalized Excitons in Light Harvesting Complexes: What are design principles for efficient and robust energy collection?
Professor Seogjoo J. Jang
Seogjoo J. Jang is a Professor of Chemistry at Queens College of the City University of New York (CUNY), and is a doctoral faculty of both Chemistry and Physics PhD programs at the Graduate Center of CUNY. He obtained his BS (1989) and MS (1993) degrees in Chemistry from Seoul National University, and a Ph.D. degree (1999) in Chemistry from the University of Pennsylvania. He then worked as a postdoctoral associate at MIT (1999-2002) and as a Goldhaber Distingushed Fellow (2003-2005) at Brookhaven National Laboratory before starting his faculty position at Queens College, CUNY in 2005. His research expertise is in quantum dynamics theories and computational modeling. In particular, he has pioneered modern theories of resonance energy transfer that are now being incorporated into theoretical analyses of experimental data on complex molecular systems, and has made key contributions to understanding the role of delocalized excitons in photosynthetic light harvesting complexes. He is a recipient of the National Science Foundation CAREER Award (2009) and the Camille Dreyfus Teacher Scholar Award (2010).
Natural organisms such as photosynthetic bacteria, algae, and plants employ complex molecular machinery to convert solar energy into biochemical fuel. An important common feature shared by most of these photosynthetic organisms is that they capture photons in the form of excitons typically delocalized over a few to tens of pigment molecules embedded in protein environments of light harvesting complexes (LHCs). Delocalized excitons created in such LHCs remain well protected despite being swayed by environmental fluctuations, and are delivered successfully to their destinations over hundred nanometer scale distances in about hundred picosecond time scales. Despite decades of research, key design principles enabling their superb light harvesting capability are not yet clearly understood at present. I will provide a brief overview of recent findings on three major LHCs, Fenna-Matthews-Olson complex of green sulfur bacteria, light harvesting 2 (LH2) complex of purple bacteria, and phycobiliproteins of cryptophyte algae, and assesses their implications in the context of achieving excellent light harvesting functionality. Then, I will explain our ongoing efforts to model the spectroscopy and the exciton dynamics of LH2 complexes. These results provide new insights into how natural systems control negative effects of disorder through interplay of structural factors, hydrogen bonding, and quantum mechanical delocalization.