Prediction of azulene-based nanographene-like materials

Abstract

Azulene-based nanographene-like materials are predicted and studied to reveal the molecular properties of these new materials. C48H18/(G-48), C68H22/(G-68), and C88H26/(G-88) nanographenes and their isomers based on azulene molecule (azulphene) as A-48, A-68, and A-88 were studied to infer general properties for large azulphene systems. Nanotubes from azulphenes are also obtained and studied. The isoelectronic graphene and azulphene materials have significant differences concerning, e.g., electric dipole, aromaticity, bond length, and bond stress. In the present studies, it was used the Density Functional Theory (DFT) and including the version of Grimme's D dispersion for the different spin multiplicities: singlet closed-shell (CS) and open-shell (OS), triplet, and quintet. For example, the ground-state of A-(48-68-88) structures is a singlet. The UV–visible spectra of all compounds exhibit maximum absorption peaks attributed to the electronic transition π→π*. The IR spectrum of G-88 and A-88 shows an intense set of absorption peaks in the range [600:1700 cm−1]. The following IR frequencies could be used to indicate azulphene structures: 1124, 1162, 1436, 1542, and 1597 cm−1. The azulphene sheets have a non-uniform distribution of the electron density, unlike graphene systems, which makes them promising candidates for regioselective chemical modification. The nucleus independent chemical shift calculations show that the five-membered rings are aromatic, and the seven-membered rings are antiaromatic similar to the azulene molecule. Our study also showed smaller diameter tubes based on azulene (C57NTs) might be more stable than their conventional C6NTs isomer.