Molecular recognition in curved π-systems: effects of π-lengthening of tubular molecules on thermodynamics and structures

The thermodynamics and molecular structure of a supramolecular complex between a tubular molecule, (<i>P</i>)-(12,8)-[4]cyclo-2,8-anthanthrenylene, and fullerene were investigated. The enthalpy-driven characteristics of the association were enhanced upon lengthening of the curved sp²-carbon networks in the tubular molecule as a result of an increase in the C-C contact areas in addition to the emergence of CH-π contacts with aliphatic chains. The involvement of CH-π interactions in the molecular recognition consequently increased the entropy cost for the association, and the importance of molecular structures at the edge of tubular molecules was revealed. An inflection-free, smooth surface inside the tubular molecule was revealed by crystallographic analysis, which allowed for dynamic motions of the encapsulated fullerene molecule in solution. This study provided a new example of a molecular peapod with a smoothly curved π-interface to be examined in the structure-thermodynamics relationship study and led to an in-depth understanding of peapods in general.