Exciton coherence lifetimes from electronic structure

TL;DR

This study uses first-principles modeling to investigate exciton coherence lifetimes in aromatic homodimers, demonstrating that despite energy inaccuracies, key coherent transport properties can be semi-quantitatively predicted.

Contribution

It shows that first-principles electronic structure calculations can semi-quantitatively reproduce exciton coherence lifetimes despite large energy errors in TDDFT.

Findings

Coherent transport timescales match experimental data.

First-principles coupling calculations reproduce fluorescence anisotropy decay.

Despite energy inaccuracies, transport properties are semi-quantitatively accurate.

Abstract

We model the coherent energy transfer of an electronic excitation within covalently linked aromatic homodimers from first-principles, to answer whether the usual models of the bath calculated via detailed electronic structure calculations can reproduce the key dynamics. For these systems the timescales of coherent transport are experimentally known from time-dependent polarization anisotropy measurements, and so we can directly assess the whether current techniques might be predictive for this phenomenon. Two choices of electronic basis states are investigated, and their relative merits discussed regarding the predictions of the perturbative model. The coupling of the electronic degrees of freedom to the nuclear degrees of freedom is calculated rather than assumed, and the fluorescence anisotropy decay is directly reproduced. Surprisingly we find that although TDDFT absolute energies are routinely in error by orders of magnitude more than the coupling energy, the coherent transport properties of these dimers can be semi-quantitatively reproduced from first-principles. The directions which must be pursued to yield predictive and reliable prediction of coherent transport are suggested.