CAMOS Seminar

Speaker : Horst Köppel
Theoretical Chemistry
University of Heidelberg
69120 Heidelberg, Germany
Topic : Nonadiabatic excited state dynamics and
photoactive biomolecular function
Date : January 14, 2007
Time : 12.30 PM
Venue : C V Raman Hall, IACS

All are cordially invited to attend.

Abstract: Conical intersections of potential energy surfaces have emerged as paradigms of nonadiabatic excited state dynamics in the past years [1]. In the talk a brief outline is given of their main characteristics, historical developments, and methodological aspects of their theoretical (ab initio quantum dynamical) treatment. These general ideas are illustrated by applying them to some prototypical small polyatomics such as acetylene [2] and the benzene cation [3,4]. The underlying system parameters are determined from modern ab initio calculations. The nuclear dynamics is studied by wavepacket propagation, often relying on the MCTDH algorithm. Typical features emerging are complex spectral structures upon electronic transitions and ultrafast internal conversion processes ( i.e. occurring in the femtosecond time range).

In the second part, the importance of these findings for photoactive biomolecular function is addressed by referring to a particular example, the photoactive yellow protein. This has received considerable attention in the recent literature, and is characterized by an ultrafast photoresponse of the chromophore, comprising a cis-trans isomerization, subsequent protonation, and (on a longer time scale) an unfolding of the protein. We have used the CC2 method to investigate the electronic spectrum of the chromophore and establish in detail the influence of the local amino acid environment on it (namely, the Arg52 residue and various hydrogen bonds) [5]. The change in electronic spectrum occurring upon single- and double-bond rotation, as well as the related charge transfer within the chromophore, strongly suggest the importance of conical intersections for the photoisomerization [6].

[1] W. Domcke, D.R. Yarkony and H. Köppel (Eds.), Conical Intersections: Electronic Structure, Dynamics and Spectroscopy (World Scientific, Singapore, 2004).

[2] B. Schubert, H. Lischka and H. Köppel, Chem. Phys. (2007), in press.

[3] H. Köppel et al., J. Chem. Phys. 117, 2657 (2002).

[4] I. Baldea and H. Köppel, J. Chem. Phys. 124, 064101 (2006).

[5] E. Gromov, I. Burghardt, L.S. Cederbaum and H. Köppel, JACS 129, 6798 (2007).

[6] E. Gromov et al., J. Photochem. and Photobiol. A 190, 241 (2007).