Diagrammatic Exciton Basis Theory of the Photophysics of Pentacene Dimers

TL;DR

This paper develops a diagrammatic exciton basis theory to analyze the photophysics of pentacene dimers, providing insights into their excited states and transient absorption spectra relevant for singlet fission applications.

Contribution

It introduces a novel diagrammatic exciton basis approach for modeling excited states in pentacene dimers, advancing understanding of their photophysical behavior.

Findings

Bound triplet-triplet states are the main photoexcitation products.

Theoretical spectra match experimental transient absorption data.

Predicted absorptions beyond 1500 nm relate to classic polyene states.

Abstract

Covalently linked acene dimers are of interest as candidates for intramolecular singlet fission. We report many-electron calculations of the energies and wavefunctions of the optical singlets, the lowest triplet exciton and the triplet-triplet biexciton, as well as the final states of excited state absorptions from these states in a family of phenyl-linked pentacene dimers. While it is difficult to distinguish between the triplet and the triplet-triplet from their transient absorptions in the 500-600 nm region, by comparing theoretical transient absorption spectra against published and unpublished experimental transient absorptions in the near and mid infrared we conclude that the end product of photoexcitation in these particular bipentacenes is the bound triplet-triplet and not free triplets. We predict additional transient absorptions at even longer wavelengths, beyond 1500 nm, to the equivalent of the classic 2$^1$A$_g^-$ in linear polyenes.