Noncovalent interactions between O₆‐corona[6]arene nanorings and fullerenes C₆₀ and C₇₀: atypical ring ball‐shaped host‐guest systems

Abstract

The host‐guest complexes formed with quasi‐triangle‐shaped O6‐corona[3]arene[3]tetrazine (T) or O6‐corona[3]arene[3]pyridazine (P) nanorings as hosts and sphere‐like fullerene C60 or C70 as guests were investigated by density functional theory calculations with solvent effect (toluene, polarizable continuum model) being taken into account. Although the triangle‐shaped host has no geometric advantage for the fullerene recognition, the stable P@C60 (C70) and T@C70 have been experimentally detected. Therefore, on the point view of geometry features, O6‐corona[6]arenes@C60 (C70) can be regarded as a kind of atypical nano‐sized host‐guest systems. The geometry optimizations showed that fullerenes are not deeply encapsulated into the cavity of hosts O6‐corona[6]arenes but in a floating position on the cavities of hosts. The correlation between the binding energy (ΔEcp) and cavity size of the host manifests that the steric effect between host and guest is the decisive factor to determine the thermodynamic stability. The thermodynamic information indicates that the host‐guest binding processes are exothermic, enthalpy driven, and entropy opposed. Qualitative analysis based on the frontier orbital features shows that the recognition contributions brought by electron effect of charge transfer stabilization between the fullerene and the O6‐corona[6]arene nanorings can be basically excluded. Fluorescence emission spectroscopy of the free O6‐corona[6]arene molecules and their host‐guest complexes formed with fullerenes (C60 or C70) were simulated by using time‐dependent density functional theory. Additionally, the host‐guest interaction regions were detected and visualized in real space based on the electron density and reduced density gradient. Furthermore, Hirshfeld surface analysis was used for the investigation on the O6‐corona[6]arenes@C60 (C70) host‐guest interactions.

Metal Atoms (Li, Na, and K) Tuning the Configuration of Pyrrole for the Selective Recognition of C60

“…Since the discovery of C 60 in 1985, fullerenes are known as famous three-dimensional super-aromatic molecules with numerous isomers. However, the determination and recognition of their geometries are huge challenges in experiments because of rigorous synthesis conditions. − Host–guest selective recognition is a powerful method to isolate and characterize the fullerenes, − and thus, reasonable hosts are desired to recognize the fullerene isomers. The well-known hosts, nanoring [ n ]­cycloparaphenylene ([ n ]­CPP) including its derivatives, are always used to recognize fullerenes, − during which the crucial step is the elucidation of the [ n ]­CPP-based fullerene host–guest geometries.…”