Switching Charge Transfer Characteristics of Quaterthiophene from p-type to n-type via Interactions with Carbon Nanotube

Carbon nanotube-based semiconductors are of great interest for optoelectronic applications at nanoscale. The present study investigates the structural, optoelectronic and charge transport properties of non-covalent complexes formed between carbon nanotube (CNT) and quaterthiophene (4T) by employing dispersion-corrected density functional methods. The effect of different functionals viz., B97-D, B3LYP-GD3 and ωB97X-D on the properties of endo- and exohedral complexes is examined. The endohedral complex (4T@CNT) is found to be energetically more stable than the exohedral one (4T-CNT). The electronic properties such as ionization energy, electron affinity and energy gap between frontier molecular orbitals of CNT are not significantly changed by the adsorption or the encapsulation of 4T. Contrary to p-type characteristics of 4T, its complexes formed with CNT exhibit n-type characteristics due to higher electron mobility than the hole mobility. Among endo- and exohedral complexes, the former one shows highest electron mobility of 3.79 cm2V-1s-1. The absorption properties of all the systems were studied by time-dependent density functional theory (TD-DFT). It is found that the complexes undergo several charge transfer transitions in the visible region of the electromagnetic spectrum. The above results unequivocally suggest that the charge-transfer characteristics of 4T can be altered on forming complexes with CNT.