An effective Hamiltonian approach for Donor-Bridge-Acceptor electronic transitions: Exploring the role of bath memory

Abstract

We present here a formally exact model for electronic transitions between an initial (donor) and final (acceptor) states linked by an intermediate (bridge) state. Our model incorporates a common set of vibrational modes that are coupled to the donor, bridge, and acceptor states and serves as a dissipative bath that destroys quantum coherence between the donor and acceptor. Taking the memory time of the bath as a free parameter, we calculate transition rates for a heuristic 3-state/2 mode Hamiltonian system parameterized to represent the energetics and couplings in a typical organic photovoltaic system. Our results indicate that if the memory time of the bath is of the order of 10-100 fs, a two-state kinetic (i.e., incoherent hopping) model will grossly underestimate overall transition rate.

Mixed Quantum Classical Simulations of Charge-Transfer Dynamics in a Model Light-Harvesting Complex. II. Transient Vibrational Analysis

“…In either case, we suspect such modes to have strong electron–vibrational coupling (large Huang–Rhys parameters (HRPs)) and should certainly be included in theoretical models. Previously, our models considered few or common normal modes, − and this work lays foundational steps toward parametrizing such models with targeted specificity, leading to a more robust description. Computing the Huang–Rhys parameters poses a difficult challenge.…”

Vibrational energy redistribution during donor–acceptor electronic energy transfer: criteria to identify subsets of active normal modes

“…Intramolecular vibrational energy transfer in organic molecules is commonly simulated with effective Hamiltonians by applying harmonic approximations to identify the pathways and lifetimes of a specific mode or bond energy relaxation 51,52,53 . For example, using a parametrized Hamiltonian describing the coupling between a set of discrete electronic states with a set of phonon oscillators in combination with golden-rule transfer rates, Bittner et al were able to identify active electron transfer vibrational coordinates in donor-acceptor systems 54,55,56,57,58 . Vibrational energy relaxation and redistribution can be monitored following the evolution in time of the kinetic energy of each ENM.…”