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Chemistry Colloquium - Greg Engel

"Quantum Mechanics and Biology: Elucidating Design Principles of Photosynthetic Energy Transfer"

Presented by Greg Engel, University of Chicago

Hosted by Wei Min

Thursday, October 24, 2013

1:30 - Meet the Speaker, Room 328 Havemeyer
4:00 - Tea & Cookies, Room 328 Havemeyer
4:30 - Seminar, Room 209 Havemeyer

Photosynthetic antenna complexes harvest light with near perfect quantum efficiency and steer excitonic motion with exquisite precision.  Optimized by evolution, these complexes exploit both incoherent (Förster) energy transfer along with coherent (wavelike) motion of energy.  We seek to isolate and copy the microscopic details of this mechanism to enable coherent energy transfer in synthetic systems.  The talk will show evidence for long-lived quantum coherence in photosynthetic complexes along with new spectroscopic techniques to probe these effects.  For example, we have created a new femtosecond optical spectroscopy by exploiting spatiotemporal gradients to image the underlying excited state dynamics within photosynthetic antenna complexes.  From our 2D electronic spectra, we find a strong and unexpected mixing between states of the chromophores and some bath modes within the system.  At the end of the talk, three new results will be discussed.  First, a new theoretical model using non-equilibrium Green’s functions will be presented; this model demonstrates that the coherences observed in time domain spectroscopy report on underlying physics with direct implications for light harvesting under incoherent excitation. Second, new results will be shown demonstrating that long-lived coherence can be engineered into a family of novel synthetic small molecules using the insights extracted from the photosynthetic work.  Finally, evidence for sequence-specific dephasing rates will be demonstrated with single amino acid substitutions lending credence to hypotheses of evolutionary fine-tuning of quantum dynamics in photosynthetic complexes.