Theory of Triplet Optical Absorption in Oligoacenes: From Naphthalene to Heptacene

TL;DR

This paper develops a detailed theoretical model for triplet optical absorption in oligoacenes from naphthalene to heptacene, using the PPP Hamiltonian and CI methods, predicting spectral features that can guide future experiments.

Contribution

It provides a comprehensive theoretical analysis of triplet states and spectra in oligoacenes up to heptacene, with predictions validated against experimental data where available.

Findings

Triplet excitation energies match experimental results.

Two dominant absorption peaks are predicted in triplet spectra.

Spectral features are polarization-dependent and experimentally testable.

Abstract

In this paper we present a detailed theory of the triplet states of oligoacenes containing up to seven rings, i.e., starting from naphthalene all the way up to heptacene. In particular, we present results on the optical absorption from the first triplet excited state $1^{3}B_{2u}^{+}$ of these oligomers, computed using the Pariser-Parr-Pople (PPP) model Hamiltonian, and a correlated electron approach employing the configuration-interaction (CI) methodology at various levels. Excitation energies of various triplets states obtained by our calculations are in good agreement with the experimental results, where available. The computed triplet spectra of oligoacenes exhibits rich structure dominated by two absorption peaks of high intensities, which are well separated in energy, and are caused by photons polarized along the conjugation direction. This prediction of ours can be tested in future experiments performed on oriented samples of oligoacenes.