March 8, 2007 Nonadiabatic quantum dynamics based upon a hierarchical electron-phonon model: exciton dissociation in semiconducting polymers Hiroyuki Tamura, †,a) Eric R. Bittner, ‡,b) and Irene Burghardt †,c) † D´epartement de Chimie, Ecole Normale Sup´erieure, 24 rue Lhomond, F–75231 Paris cedex 05, France ‡ Department of Chemistry and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204, USA Abstract A hierarchical electron-phonon coupling model is applied to describe the ultrafast decay of a photogenerated exciton at a donor-acceptor polymer heterojunction, via a vibronic coupling mechanism by which a charge-localized interfacial state is created. Expanding upon an earlier Communication [Tamura, Bittner, Burghardt, J. Chem. Phys. 126, 021103 (2007)], we present a quantum-dynamical analysis based upon a two-state linear vibronic coupling model, which accounts for a two-band phonon bath including high-frequency C=C stretch modes and low-frequency ring torsional modes. Building upon this model, an analysis in terms of a hierarchical chain of effective modes is carried out, whose construction is detailed in the present paper. The effective-mode analysis highlights (i) the dominance of the high-frequency modes in the coupling to the electronic subsystem and (ii) the key role of the low-frequency modes in the intramolecular vibrational redistribution process that is essential in mediating the decay to the charge-localized state. Due to this dynamical interplay, the effective-mode hierarchy has to be carried beyond the first order in order to obtain a qualitatively correct picture of the nonadiabatic process. A reduced model of the dynamics including a Markovian closure of the hierarchy is presented. Dynamical calculations were carried out using the multiconfiguration time-dependent Hartree method. a) Electronic mail: tamura@ens.fr b) Electronic mail: bittner@uh.edu c) Electronic mail: irene.burghardt@ens.fr 1