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biphenylene_preprint.pdf (5.62 MB)

Exploitation of Baird Aromaticity and Clar's Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

preprint
submitted on 02.03.2021, 19:54 and posted on 03.03.2021, 12:56 by Felix Plasser
Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four PAHs based on the biphenylene motif finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). These results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

Funding

EPSRC EP/V048686/1

History

Email Address of Submitting Author

f.plasser@lboro.ac.uk

Institution

Loughborough University

Country

United Kingdom

ORCID For Submitting Author

0000-0003-0751-148X

Declaration of Conflict of Interest

No conflicts to declare.

Version Notes

Preprint before submission.

Exports