Interconvertible Helical Adsorption of Triptycene-Phenazine Molecules on Carbon Nanotubes Driven by Interfacial Interactions

Abstract

Hybrid structures composed of triptycene–phenazine (Trip-Phz) molecules and carbon nanotubes have been experimentally reported to exhibit unique electrochemical properties; however, their molecular-level structures remain unclear. In this study, we investigate the adsorption structures and energetics of Trip-Phz molecules on carbon nanotubes using dispersion-corrected density functional theory (DFT) calculations. The calculations reveal that interfacial π–π interactions between Trip-Phz molecules and the nanotube are stronger than intermolecular π–π interactions, leading to the preferential formation of a directly attached first adsorption layer. Within this layer, molecular orientations are governed by intermolecular CH···N hydrogen bonds, resulting in three nearly isoenergetic adsorption configurations characterized by rotation angles of approximately 20°, 45°, and 85°. The two lowest-energy configurations, with rotation angles of approximately 20° and 45°, are separated by a relatively small activation barrier, suggesting that they are readily interconvertible under ambient conditions. As the number of adsorbed molecules increases, these rotational relationships are preserved, giving rise to helical adsorption structures that are additively stabilized by interfacial and intermolecular interactions. For adsorption on nanotube bundles, structures with the smallest rotation angle (∼20°) are energetically favored. Importantly, the interfacial interactions disrupt the ideal hydrogen-bonded honeycomb network observed in the crystal structure, leading to nonuniform molecular arrangements with unpaired nitrogen atoms. This structural feature enables proton accommodation and provides a molecular-level explanation for the experimentally observed electrochemical properties.