Abstract

Efficient and affordable synthetic nanometric hosts able to incorporate different species have attracted attention for further exploration of changes in chemical properties and reactivity at the nanomolecular scale. The recent incorporation of suit[3]ane, involving a host composed by two parallel hexameric platforms alternating pyridinium and phenyl rings, bridged by three p-phenylene units (Hexacage+6), results in a mechanically interlocked nanometric host–guest pairs. In such species, the host structure follows the contour of the guest, extends the well-developed use of charged pyridinium-based structures to Hexacage+6, and the use of benzotrithiophene (BTT) and its alkylated derivative (THBTT). Our results show a sizable stabilization of -119.0 kcal mol−1, in the formation of the host–guest complex, with a relevant London dispersion character contributing by ~ 60% of the stabilizing factors. This result accounts for the extended and π⋯π and C–H⋯π surface given by the BTT-aromatic core and the hexyl chains, respectively, towards the HexaCage6+ moiety in suit[3]ane. In addition, polarization and electrostatic character also contribute to the stabilization of the host–guest complex. The removal of the alkyl chains of THBTT leads to BTT, for which the interaction energy with the HexaCage6+, decreases to − 49.1 kcal mol−1, denoting the enhanced stabilization introduced by the alkyl moieties. The origin of the observed shielding patterns from 1H-NMR experiments was also revisited. Lastly, the understanding of the role from different stabilizing terms is useful for further rationalization and design of selective and enhanced hosts towards more versatile and tunable hosts. Charge transfer integrals in the host–guest species (THBTT⊂HexaCage6+ and BTT⊂HexaCage6+) were directly evaluated as the matrix elements of Kohn–Sham Hamiltonian, defined in terms of molecular orbitals of individual host and guest molecules. Our findings are totally in line with EDA results indicating that electron transfer is not the most significant process to the host–guest stabilization. Graphical abstract: [Figure not available: see fulltext.] Fundamental analysis of mechanically interlocked structures at the nanomolecular scale, allows envisaging further nanometric molecular machines. Explanation of the Abstract graphics: Since the formation of the host–guest structure leads to a mechanically interlocked device, a shocking picture with stunning colors, denoting inclusion and motion was selected for the art.