Abstract

Exciton diffusion is of key importance for the efficiency of light harvesting in organic electronic materials and biological photosystems. The microscopic mechanisms of exciton transport vary considerably, from hopping type processes described by rate theories to adiabatic quantum transport of delocalized excitonic species. Inall dynamical regimes, the coupling between electronic excitations and vibrational degrees of freedom plays a crucial role, even though the resulting diffusion processes can differ. In order to capture the interplay of exciton motion and vibronic effects, we use efficient tensor network methods of Multi-Layer Multiconfiguration Time-Dependent Hartree (ML-MCTDH) type [1] and analogous Gaussian wavepacket based methods [2] to describe intra-chain and inter-chain exciton transport based on first-principles parametrized potentials [3,4]. Emphasis is placed on the cooperation between polaronictrapping due to high-frequency modes and thermal activation due to low-frequency soft modes which drive a diffusive exciton dynamics [3-5]. Different transport regimes are identified, ranging from adiabatic transport to a transient localization regime [5]. Theseobservations are complemented by simulations of two-dimensional electronic spectroscopy (2DES) signals which highlight coherent vibronic effects and spectral diffusion due to conformational fluctuations [6].

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[2] P. Eisenbrandt, M. Ruckenbauer, S. Roemer, I. Burghardt, J. Chem. Phys. 149, 174101 (2018).

[3] R. Binder, I. Burghardt, Faraday Discuss., 221, 406-427 (2020).

[4] W. Popp, D. Brey, R. Binder, I Burghardt, Annu. Rev. Phys. Chem., 72, 591-616 (2021).

[5] D. Brey, I. Burghardt, J. Phys. Chem. Lett. 15, 1836–1845 (2024).

[6] D. Brey, I. Burghardt, J. Chem. Phys. 162, 244112 (2025).