Analysis of the host-guest complex formation involving bridged hexameric pyridinium-phenyl rings in the HexaCage6+ host in suit[3]ane: insights from dispersion-corrected DFT calculations for a nanometric mechanically interlocked device

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 similar to 60% of the stabilizing factors. This result accounts for the extended and pi center dot center dot center dot pi and C-H center dot center dot center dot pi surface given by the BTT-aromatic core and the hexyl chains, respectively, towards the HexaCage(6+) 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 HexaCage(6+), decreases to - 49.1 kcal mol(-1), denoting the enhanced stabilization introduced by the alkyl moieties. The origin of the observed shielding patterns from H-1-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 subset of HexaCage(6+) and BTT subset of HexaCage(6+)) 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. [GRAPHICS] .

Automated summary

Efficient and affordable synthetic nanometric hosts have attracted attention for exploring changes in chemical properties and reactivity at the nanomolecular scale. Recent research has shown that the incorporation of suit[3]ane results in mechanically interlocked nanometric host-guest pairs. The London dispersion force plays a significant role in the stabilization of the host-guest complex.