Pagoda[4]arene and i-Pagoda[4]arene

A new type of macrocyclic arenes, named pagoda[4]arene (P4) and i-pagoda[4]arene (i-P4), were conveniently synthesized by the TFA-catalyzed one-pot condensation of 2,6-dimethoxylanthracene and paraformaldehyde in dichloromethane at room temperature. P4 and i-P4 showed unique square pagoda structures and fixed conformations in solution and also exhibited strong blue fluorescence. Moreover, P4 and i-P4 with deep and rich-electron cavities could not only encapsulate n-hexane and one or two dichloromethane molecules in the solid state but also showed strong binding abilities toward neutral dinitriles with different chain lengths and various nitrogen-containing heterocyclic salts to form 1:1 stable host-guest complexes in both solution and the solid state. In particular, it was also found that with the increase in the alkyl chain length of the dinitriles, the association constants for their complexes with both P4 and i-P4 were markedly increased from glutaronitrile to octanedinitrile as a result of the deep cavities of the macrocycles and multiple intermolecular interactions. Since P4 and i-P4 had stable planar chirality, their efficient resolutions were further achieved by HPLC with a chiral column. Interestingly, the two enantiomers showed mirror-imaged CD signals and excellent CPL properties, which could allow them to have potential applications in chiral luminescent materials.