Nature of Noncovalent Interactions in the [n]Cycloparaphenylene⊃C70 (n = 10, 11, and 12) Host–Guest Complexes: A Theoretical Insight into the Shortest C70–Carbon Nanotube Peapod

Abstract

The encapsulations of fullerene C70 by carbon-nanorings are of great interest because, unlike the spheroidal C60, several distinct geometrical orientations are possible. Additionally, due to experimental difficulties, there is a great deal of opportunity for the computational efforts to deeply explore the intrinsic nature of π–π noncovalent interactions of the CPP carbon-nanoring⊃fullerene host–guest systems. In this paper, the structures and properties of the host–guest complexes formed with nanoring host [n]cycloparaphenylene (n =10, 11, and 12) ([n]CPP) and guest fullerene C70 were detailed and explored by theoretical calculations. The results showed that three different kinds of quasi-inclusion configurations can be obtained for [10]CPP⊃C70 and [11]CPP⊃C70 host–guest complexes in which C70 is lying, half-lying, and standing in the cavities of the hosts, respectively. However, there are only two kinds of stable configurations for [12]CPP⊃C70 host–guest complexes in which C70 is half-lying and standing in the cavities of the host [12]CPP, respectively. According to the relative values of the binding energies and thermodynamic information, the guest C70 is apt to adopt lying, standing, and half-lying orientations in the cavities of [10]CPP, [11]CPP, and [12]CPP, respectively. The host–guest interaction regions were detected and visualized in real space based on the electron density and reduced density gradient (RDG). Additionally, IR, UV–visible–NIR, and 1H NMR spectra of the hosts before and after the formations of the complexes have been simulated and discussed qualitatively, which may be helpful for further experimental investigations in the future.