Pagoda[4]arene and <i>i</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.