Selectivity and Cooperativity in the Binding of Multiple Guests to a Pillar[5]arene–Crown Ether Fused Tricyclic Host

A novel tricylic host molecule <b>1</b> that consists of two pillar[5]­arene units and a crown ether ring was found to selectively bind two kinds of guest molecules with different shapes, sizes, and electronic constitutions, namely 1,4-dicyanobutane <b>G1</b> and paraquat <b>G2</b>, with its two macrocyclic subunits, to form a four-component complex <b>2G1⊂1⊃G2</b>. An ¹H NMR study of stepwise bindings of <b>G1</b> and <b>G2</b> to host <b>1</b> in CDCl₃/DMSO-<i>d</i>₆ revealed that the strength of the association between complex <b>2G1⊂1</b> and guest <b>G2</b> was only one-fourth of that between free <b>1</b> and <b>G2</b>, demonstrating a negative heterotropic cooperativity of <b>G1</b> in the binding of <b>G2</b> to host <b>1