Self-assembled cyclic oligothiophene nanotubes: electronic properties from a dispersion-corrected hybrid functional

The band structure and size-scaling of electronic properties in self-assembled cyclic oligothiophene nanotubes are investigated using density functional theory (DFT) for the first time. In these unique tubular aggregates, the {\pi}-{\pi} stacking interactions between adjacent monomers provide pathways for charge transport and energy migration along the periodic one-dimensional nanostructure. In order to simultaneously describe both the {\pi}-{\pi} stacking interactions and the global electronic band structure of these nanotubes, we utilize a dispersion-corrected B3LYP-D hybrid functional in conjunction with all-electron basis sets and one-dimensional periodic boundary conditions. Based on our B3LYP-D calculations, we present simple analytical formulas for estimating the fundamental band gaps of these unique nanotubes as a function of size and diameter. Our results on these molecular nanostructures indicate that all of the oligothiophene nanotubes are direct-gap semiconductors with band gaps ranging from 0.9 eV - 3.3 eV, depending on tube diameter and oligothiophene orientation. These nanotubes have cohesive energies of up to 2.43 eV per monomer, indicating future potential use in organic electronic devices due to their tunable electronic band structure and high structural stability.