A Triptycene-Based Cage Host for Aromatic Hydrocarbon Guests

A macrocyclic compound consisting of two triptycene units and three diphenylacetylene bridges was designed as a molecular cage with a small cavity. The target compound was synthesized by the Sonogashira coupling between two kinds of 2,7,14-triphenyltriptycene precursors. The DFT calculation revealed that this cage molecule had a D3 symmetric structure with a cavity of 3.6 & Aring; in height. When this cage was mixed with aromatic compounds such as anthracene, the signal due to the triptycene H atoms at the inner bridgehead positions significantly shifted upfield in the 1H NMR spectra. For anthracene, acenaphthylene, and pyrene guests, the association constants Ka for the formation of cage-guest 1 : 1 inclusion complexes were determined to be ca. 10 L mol-1 at 298 K in CDCl3 by the NMR titration measurements. The noncovalent interaction plot suggested that C-H & sdot;& sdot;& sdot;pi interactions played an important role in the host-guest complexes. The host ability of the cage to various aromatic guests is discussed in terms of the size and shape fitting based on the experimental and DFT calculation data.