Theoretical Study of New Acceptor and Donor Molecules based on Polycyclic Aromatic Hydrocarbons

TL;DR

This study uses computational methods to analyze the electronic structure of novel polycyclic aromatic hydrocarbons, providing insights into their donor and acceptor properties relevant for electronic applications.

Contribution

It introduces a numerical approach combining DFT and DELTA-SCF to characterize the electronic properties of new PAHs, complementing experimental UPS data.

Findings

Coronene-hexaone exhibits high electron affinity, similar to TCNQ.

Calculated HOMO-LUMO gaps agree with experimental excitation energies.

TD-DFT accurately predicts optical gaps.

Abstract

Functionalized polcyclic aromatic hydrocarbons (PAHs) are an interesting class of molecules in which the electronic state of the graphene-like hydrocarbon part is tuned by the functional group. Searching for new types of donor and acceptor molecules, a set of new PAHs has recently been investigated experimentally using ultraviolet photoelectron spectroscopy (UPS). In this work, the electronic structure of the PAHs is studied numerically with the help of B3LYP hybrid density functionals. Using the DELTA-SCF method, electron binding energies have been determined which affirm, specify and complement the UPS data. Symmetry properties of molecular orbitals are analyzed for a categorization and an estimate of the related signal strength. While SIGMA-like orbitals are difficult to detect in UPS spectra of condensed film, calculation provides a detailed insight into the hidden parts of the electronic structure of donor and acceptor molecules. In addition, a diffuse basis set (6-311++G**) was used to calculate electron affinity and LUMO eigenvalues. The calculated electron affinity (EA) provides a classification of the donor/acceptor properties of the studied molecules. Coronene-hexaone shows a high EA, comparable to TCNQ, which is a well-known classical acceptor. Calculated HOMO-LUMO gaps using the related eigenvalues have a good agreement with the experimental lowest excitation energies. TD-DFT also accurately predicts the measured optical gap.