The non-adiabatic dynamics of cis-trans photoisomerization in polyatomic systems is investigated using a model Hamiltonian, which exploits the approximate separation of the photochromic unit from the rest of the molecular degrees of freedom. The dynamical response of the active modes upon photoexcitation is described using wavepacket propagation while the remaining modes are treated classically, explicitly taking into account the coupling between both subsystems via the symplectic PICKABACK algorithm [1]. The model enables a microscopic description of the non-radiative excited-state lifetime and the isomerization yield, as well as the time evolution of the configurational rearrangement and the internal energy redistribution. (C) 2013 Elsevier B.V. All rights reserved.