Local aromaticity of linear cata-benzocoronenes and acenes: density functional study

A computational study using density functional theory is reported for the coronene monomer and selected linear cata-benzocoronene oligomers. Local aromaticity was discussed and analysed using the theoretical Harmonic Oscillator Model of the Electron Delocalisation (HOMED) index and its geometric (GEO) and energetic (EN) contributions. The [n]acenes (n = 3, 7, 11 and 15) served as reference molecules. Local aromaticity of individual superbenzene rings has oscillating character. On the other hand, the highest HOMED parameters which are practically independent on the molecular lengths were found for the smallest molecules including condensed benzene rings in their structure. For the largest structure of [n]acenes (n = 15), the inner rings are less aromatic than the outer ones. Depending on the molecular length, the energy gaps between the B3LYP energy levels of the highest occupied and lowest unoccupied molecular orbitals vary from 2.71 eV to 4.04 eV for coronene series and from 0.61 eV to 3.59 eV for [n]acenes.