Theoretical Investigation of the Defect Position Effect on the Aromaticity of N and B Doped Graphene

The NICS index is a simple, easy and reference independent method to evaluate the aromaticity of molecules. When cyclic compounds with delocalized π-electrons are subjected to the external magnetic field perpendicular to the ring, the π-electrons in the closed-circuit provide a ring current. This circular ring current produces an induced magnetic field, opposite the external one. Shielding of the external magnetic field will be intensified by the nuclear magnetic resonance chemical shift[1]. Schleyer et al.[2] efforts lead to a method to calculate the chemical shift not only at every nucleus but also at any point in the space in the vicinity of molecules. NICS is the negative of the isotropic component of the chemical shielding tensor. It is very often to calculate NICS at the geometric center of the ring. To avoid the shielding effects of the framework of electrons, calculations usually are carried out at points 1Å above the center of rings. The magnetic shielding tensor is considered as a better descriptor of aromaticity[3]. In this research, the effect of defection position on the aromaticity of N and B doped graphene diradicals has been investigated. Such a study helps to understand, control and improve the unique features of graphene-based materials. Considering the values of the constituting rings of studied species improves that, defection in the marginal area has the least effect on the aromaticity of graphene.