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SUMMARY:The Quantum Design of Photosynthesis - Prof. R. van Grondelle\, VU
  University
DTSTART:20131024T131500Z
DTEND:20131024T141500Z
UID:TALK46215@talks.cam.ac.uk
CONTACT:Gareth Conduit
DESCRIPTION:Photosynthesis has found an ultrafast and highly efficient way
  of converting the energy of the sun into electrochemical energy. The sola
 r energy is collected by Light-Harvesting complexes (LHC) and then transfe
 rred to the Reaction Center (RC) where the excitation energy is converted 
 into a charge separated state with almost 100% efficiency. That separation
  of charges creates an electrochemical gradient across the photosynthetic 
 membrane which ultimately powers the photosynthetic organism. The understa
 nding of the molecular mechanisms of light harvesting and charge separatio
 n will provide a template for the design of efficient artificial solar ene
 rgy conversion systems.\n\nUpon excitation of the photosynthetic system th
 e energy is delocalized over several cofactors creating collective excited
  states (excitons) that provide efficient and ultrafast paths energy trans
 fer using the principles of quantum mechanics. In the reaction center the 
 excitons become mixed with charge transfer (CT) character (exciton-CT stat
 es)\, which provide ultrafast channels for charge transfer. However\, both
  the LHC and the RC have to cope with a counter effect: disorder. The slow
  protein motions (static disorder) produce slightly different conformation
 s which\, in turn\, modulate the energy of the exciton-CT states. In this 
 scenario\, in some of the LHC/RC complexes within the sample ensemble the 
 energy could be trapped in some unproductive states leading to unacceptabl
 e energy losses.\n\nHere I will show that LHCs and RCs have found a unique
  solution for overcoming this barrier: they use the principles of quantum 
 mechanics to probe many possible pathways at the same time and to select t
 he most efficient one that fits their realization of the disorder. They us
 e electronic coherence for ultrafast energy and electron transfer and have
  selected specific vibrations to sustain those coherences. In this way pho
 tosynthetic energy transfer and charge separation have achieved their amaz
 ing efficiency. At the same time these same interactions are used to photo
 protect the system against unwanted byproducts of light harvesting and cha
 rge separation at high light intensities.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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