Thermodynamic, optical, and nonlinear optical properties of self-assembled nanotube via stacking of belt[8]pyridine with and without oriented external electric field

Nanotubes, formed through the self-assembly of nanobelts, have attracted great interest in supramolecular chemistry due to their unique characteristics. However, the complete understanding of the self-assembly of nanobelts into nanotubes is not well understood. In this study, Density functional theory (DFT) calculations were performed to get insight into geometric, electronic, thermodynamic, optical, and nonlinear optical properties of supramolecular self-assembled belt[8]pyridine systems. The Binding energies, Gibbs free energies, and Zero-point energies confirmed the stability of these belts. The NCI analysis depicted that the dispersion and electrostatic interactions between the monomers play a key role in driving self-assembly of belts, leading to the formation of the nanotubes. The Frontier molecular orbital (FMO) and natural bond orbital (NBO) analyses have been performed to study the electronic properties, global reactivity descriptors, and charge transfer. Electronic and optical properties for an infinite self-assembled nanotube were obtained through extrapolation by polynomial fit using the oligomer approach. Moreover, the oriented external electric field (OEEF) of strength 0.001 to 0.005 au was applied to understand its influence on the electronic and optical properties of the designed supramolecular systems. The results showed that nonlinear optical properties tend to increase with the size of the tube, whereas the H-L_gap showed a decreasing trend under applied field. This unusual behavior is due to the phenomenon of dipole torque in higher belts. This research may yield novel insights into the creation of supramolecular nanobelts and optical sensors.