Comparative study of cyclic polyaniline oligomers with linear and bent structures

Abstract

In the present work, Grimme’s D3 dispersion corrected density functional theory (DFT-D3) is used for the comparative study of cyclic polyaniline oligomers with linear and bent structures, for the first time. Molecular design and spectral characterisation of these compounds are performed at the B3LYP-D3/6-311G(d,p) and the B3LYP-D3/6-311++G(d,p) levels of theory. The formation mechanism of cyclic polyaniline oligomers compared to the linear and bent structures is discussed. Molecular orbital (MO) calculations are applied to study the electronic structure, and estimate the energy gap between the highest occupied (HOMO) and the lowest unoccupied (LUMO) molecular orbitals. The density of states (DOS) diagrams are used to evaluate the nature of valence and conduction bands and investigate the electrical conductivity. The calculated infrared (IR), ultraviolet-visible (UV-Vis) and nitrogen-15 nuclear magnetic resonance (15N NMR) spectra of these compounds are compared to the theoretical and experimental spectra of polyaniline. Results show that cyclic polyanilines are nonpolar in comparison to the linear and bent structures. The band gap of these molecules is larger than the linear and bent ones. The band gap of cyclic oligomers increases with the increasing size of the rings. These results provide useful information for the characterisation of these novel compounds.