Structural, optoelectronic and charge transport properties of the complexes of indigo encapsulated in carbon nanotubes

Switching the charge transfer characteristics of quaterthiophene from p-type to n-type via interactions with carbon nanotubes

Carbon nanotube-based semiconductors are of great interest for optoelectronic applications at the nanoscale. The present study investigates the structural, optoelectronic and charge transport properties of non-covalent complexes formed between carbon nanotubes (CNTs) 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). Electronic properties such as the ionization energy, electron affinity and energy gap between the frontier molecular orbitals of the CNT are not significantly changed by the adsorption or the encapsulation of 4T. Contrary to the p-type characteristics of 4T, its complexes formed with CNTs exhibit n-type characteristics due to the higher electron mobility than the hole mobility. Among the endo- and exohedral complexes, the former one shows the highest electron mobility of 3.79 cm2 V-1 s-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 CNTs.

New Light on Molecule-Nanotube Hybrids

Optoelectronics benefits from outstanding new nanomaterials that provide emission and detection in the visible and near-infrared range, photoswitches, two level systems for single photon emission, etc. Among these, carbon nanotubes are envisioned as game changers despite difficult handling and control over chirality burdening their use. However, recent breakthroughs on hybrid carbon nanotubes have established nanotubes as pioneers for a new family of building blocks for optics and quantum optics. Functionalization of carbon nanotubes with molecules or polymers not only preserves the nanotube properties from the environment, but also promotes new performance abilities to the resulting hybrids. Photoluminescence and Raman signals are enhanced in the hybrids, which questions the nature of the electronic coupling between nanotube and molecules. Furthermore, coupling to optical cavities dramatically enhances single photon emission, which operates up to room temperature. This new light on nanotube hybrids shows their potential to push optoelectronics a step forward.