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Abstract:
Functionalized polycyclic 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 theoretically 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. (c) 2010 Elsevier Inc. All rights reserved.
