BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Conical Intersection Dynamics in Rhodopsin and its 9-cis Isorhodop
 sin analog studied with femtosecond pump-probe spectroscopy. - Dario Polli
 \, Politecnico di Milano\, Italy
DTSTART:20110210T143000Z
DTEND:20110210T153000Z
UID:TALK29815@talks.cam.ac.uk
CONTACT:Jenny Clark
DESCRIPTION:Light perception is based on a cascade of complex biochemical 
 reactions whose first step is the ultrafast (completed in about 200 fs) an
 d efficient (0.65 quantum yield) isomerisation of the retinal chromophore 
 of rhodopsin around the 11=12 double bond from the 11-cis to the all-trans
  form. It is now well established that rhodopsin's unique reactivity is me
 diated by conical intersections (CIs)\, i.e. singularities on the potentia
 l energy surfaces (PES) that form a multi-dimensional ‘seam’ connectin
 g the ground and excited states at isoenergetic points. CIs are ubiquitous
  features in theoretical descriptions of organic photochemistry and are re
 sponsible for triggering radiationless decay and efficient and ultrafast c
 onversion of photon energy into chemical energy.\n\nAn important open ques
 tion is understanding how the topography around a seam affects the dynamic
 s of transitions between electronic states at CIs. This can be addressed b
 y studying analogs of the visual pigment. In this work\, using broadband s
 ub-20-fs ultrafast spectroscopy\, we compare the CI dynamics of rhodopsin 
 with that of isorhodopsin\, containing a 9-cis retinal which isomerizes ar
 ound the 9=10 double bond and has a significantly lower quantum yield of o
 nly 0.22. \n\nWe find that in rhodopsin the wavepacket reaches the CI in a
 bout 75 fs\, after which it leaves the excited state of the reactant. This
  suggests that the CI seam has a strongly “peaked” topography. In isor
 hodopsin the wavepacket stays significantly longer in the excited state of
  the reactant\, and observe oscillations both in the reactant stimulated e
 mission (SE) decay and in the product photoinduced absorption (PA) build-u
 p\, which suggest multiple crossings of the CI.
LOCATION:Kapitza Building Seminar Room\, Cavendish Laboratory\, Department
  of Physics
END:VEVENT
END:VCALENDAR