Exciton dissociation at donor-acceptor polymer heterojunctions: quantum nonadiabatic dynamics and effective-mode analysis

TL;DR

This paper investigates the quantum dynamics of exciton dissociation at a polymer heterojunction, revealing the roles of high- and low-frequency vibrational modes and introducing an effective-mode analysis to understand nonadiabatic processes.

Contribution

It introduces a novel effective-mode representation and applies quantum dynamical simulations to elucidate exciton dissociation mechanisms at heterojunctions.

Findings

Coherent oscillations observed during initial relaxation.

Nonadiabatic decay occurs near a conical intersection hypersurface.

Low-frequency modes play a crucial role in the dynamics.

Abstract

The quantum-dynamical mechanism of photoinduced subpicosecond exciton dissociation and the concomitant formation of a charge-separated state at a TFB:F8BT polymer heterojunction is elucidated. The analysis is based upon a two-state vibronic coupling Hamiltonian including an explicit 24-mode representation of a phonon bath comprising high-frequency (C$=$C stretch) and low-frequency (torsional) modes. The initial relaxation behavior is characterized by coherent oscillations, along with the decay through an extended nonadiabatic coupling region. This region is located in the vicinity of a conical intersection hypersurface. A central ingredient of the analysis is a novel effective mode representation, which highlights the role of the low-frequency modes in the nonadiabatic dynamics. Quantum dynamical simulations were carried out using the multiconfiguration time-dependent Hartree (MCTDH) method.