Aromaticity study of singlet- and triplet-state corannulene dianion and dication

Abstract

Aromaticity rules in the ground singlet state and the first excited triplet state are exactly opposite, as shown by Baird. Thus, (4n + 2)π electron annulenes are antiaromatic and 4nπ annulenes are aromatic in their triplet state. In this work, we employ quantum-mechanical calculations at the density functional theory (DFT) level to examine (anti)aromaticity of singlet and triplet corannulene dianion and dication in their bowl-shaped ground-state structure and planar transition-state structure. We find that singlet dianion contains aromatic hub and antiaromatic rim, whereas singlet dication is an antiaromatic system. This agrees with previous calculations of current density induced by perpendicular magnetic field. For triplet dianion, we find that it can be described as having aromatic rim and nonaromatic hub. Triplet dication was found to be nonaromatic, though in planar transition-state structure, locally and semiglobally antiaromatic naphthalene subunit and aromatic central ring can be discerned.