A Simple Hubbard Model for the Excited States of $\pi$ Conjugated -acene Molecules

TL;DR

This paper introduces a simple Hubbard model to accurately describe the excited states of $cene$ molecules, providing insights into their electronic behavior and two-photon absorption properties relevant for organic electronics.

Contribution

It develops a semi-analytic Hubbard model for $cene$ excited states, enabling analysis of electron-hole behavior and optical properties with reasonable accuracy.

Findings

The model accurately predicts low-lying excitations in $cene$ molecules.

Electrons and holes in the doubly excited state behave in a triplet-like manner.

Two-photon absorption per density is comparable to other organic molecules.

Abstract

In this paper we present a model for the electronic excited states of $\pi$ conjugated -acene molecules such as tetracene, pentacene, and hexacene. We use a simple Hubbard model with a limited basis to describe the low lying excitations with reasonable quantitative accuracy. We are able to produce semi-analytic wavefunctions for the electronic states of the system, which allows us to compute the density correlation functions for various states such as the ground state, the first two singly excited states, and the lowest lying doubly excited state. We show that in this lowest lying doubly excited state, a state speculated to play a role in the singlet fission process, the electrons and holes behave in a triplet-like manner. We also compute the two-photon absorption of these -acenes, and show that per number density it is comparable to that of other organic molecules such as coronene and hexa-peri-hexabenzocoronene (HBC).