Vibronic effects in basic molecular aspects of solar energy conversion: light harvesting, charge and energy transfe

Vibronic effects in basic molecular aspects of solar energy conversion: light harvesting, charge and energy transfer Francisco Avila, Vincenzo Barone, Chiara Cappelli, , Alessandro Lami, David Picconi, Fabrizio Santoro The role played by vibronic effects in the mechanisms underlying the basic steps of solar energy harvesting and conversion at molecular level has not been fully addressed yet. Its theoretical description is very challenging due to the complexity of the phenomena and the typically large dimensions of the systems of practical interest, for example in dye sensitized solar cells or artificial photosynthesis. We have recently developed a number of computational methods to describe the role of vibrational motions in determining the shape of steady-state electronic spectra and the dynamics of photoinduced processes. Our methods have been tailored to deal with large systems and to describe vibronic effects according to a fully quantum approach. As far as spectra lineshapes are concerned, our time-independent methods allow to fully describe the vibrational structure in a exact way in harmonic approximation [1-5]. Photoinduced dynamics triggered by nonadiabatic interactions is simulated through the definition of effective modes, derived by hierarchical transformations of the Hamiltonian, and able to describe exactly the short-time dynamics of the full-dimensionality systems[6]. Our methodology have been recently applied for example to the study of the dynamics of coupled exciton and charge-transfer states in photoexcited DNA[7]. In this contribution we present some applications systems of interest for direct solar energy conversion in DSSC and in prototype systems for artificial photosynthesis. In DSSC we will report our results both the electronic spectroscopy and the dynamics of elementary processes like charge-localization within the dye. For artificial photosynthetic systems we will present our first attempts to investigate the role of vibronic effects in donor-acceptor energy transfers and if/how they can be monitored through 2D optical spectra that nowadays represent one of the most powerful experimental tools to investigate the dynamics of such phenomena . [1] F. Santoro, R. Improta, A. Lami, J. Bloino, V. Barone, J. Chem. Phys. . 2007, 126, 084509 [2] F. Santoro, R. Improta, A. Lami, J. Bloino, V. Barone, J. Chem. Phys. 2008, 128, 224311 [3] J. Bloino, M. Biczysko, F. Santoro, V. Barone, J. Comp. Theory and Comp. 2010, 6, 1256 [4] M. Biczysko, J. Bloino, F. Santoro, and V. Barone, in Computational Strategies for Spectroscopy: from Small Molecules to Nanosystems, edited by V. Barone, chap. 8, p. 361 (John Wiley & Sons, 2011). [5] F. Avila, F: Santoro, PCCP submitted [6] D. Picconi, A. Lami, F. Santoro, J. Chem. Phys Submitted. [7] R. Improta, F. Santoro, V. Barone, A. Lami, J. Phys. Chem. A 2009, 113, 15346