Time：Aug.25 2010 PM 14:00
Location：Meeting Room of state key labratory of molecular reaction dynamics building on floor 3
Prof. Tonu Pullerits
Chemical Physics, Lund University, Sweden
Abstract：Contact：Keli Han, Wei Wu
Coherent multidimensional electronic spectroscopy has been applied to various carotenoid molecules in solution. Combined modelling of the time-evolution of various photon echo signals as well as comparison to published pump-probe data allow us to draw conclusions on both the electronic structure of the carotenoids, as well as on the spectral densities giving rise to the observed optical lineshapes and dynamics(1). To account for the experimental observations on all timescales we need to include a transition in the visible spectral range from the first optically allowed excited state (S2→Sn2). Recently we have carried out double quantum coherence electronic 2D spectroscopy experiments on β-carotene proving the existence of this transition.(2) This means that any analyses of ultrafast nonlinear spectroscopy signals of carotenoids has to include this transition. Furthermore, we investigate the role and nature of the S* state, controversially debated in numerous previous studies. Based on the analysis of Feynman diagrams and one quantum coherence electronic 2D experiments of β-carotene, we show that the properties of S*-related signals can only be accounted for if S* is an excited electronic state.(3) Careful considerations of our own results and existing literature lead us to the conclusion that S* corresponds to S1 of a carotenoid with different ground state conformation.