Six-Cyclic Crown Ether-Type Pillar[5]Arene: Enhanced Binding Ability to Bispyridinium Derivatives.

A six-cyclic crown ether-type pillar[5]arene was synthesized, and the five ethylene oxide loops were located outside the cavity and not affected by temperature changes which was confirmed by variable-temperature NMR experiment in DMSO-d6 and CDCl 3 and 2D 1 H- 1 H NOESY experiment in CDCl 3 . The six-cyclic pillar[5]-crown also showed greater binding ability of host-guest with bis(pyridinium) derivatives than conventional alkoxy pillar[5]arenes that illustrated through 1 H NMR titration spectroscopic experiment in acetone-d6/CDCl 3 (1 : 1) and UV-vis titration experiments in CHCl 3 at room temperature. The five benzocrown ethers at the periphery were able to bind metal cations by 1 H NMR titration spectroscopic experiment in CD 2 Cl 2 /methanol-d4(9 : 1).