Anion-mediated encapsulation-induced emission enhancement of an IrIII complex within a resorcin[4]arene hexameric capsule

Abstract

Understanding of encapsulation processes in confined inner spaces of self-assembled hosts is important for the rational creation of supramolecular systems showing unusual reactivities and physical properties through molecular recognition. Herein we report the formation of luminescent supramolecular host–guest complexes consisting of a hydrogen-bonded resorcin[4]arene hexameric capsule and a variety of emissive Ir complex salts. The Ir complexes, accompanied by small counter anions (Cl⁻, Br⁻, NO₂⁻, I⁻ and NO₃⁻), are trapped effectively to show large encapsulation-induced emission enhancement (EIEE) behavior, while Ir complexes having large counter anions (ClO₄⁻, PF₆⁻ and OTf⁻) are not stabilized within the capsule, suggesting that the Ir complex cation is trapped together with its counter anion to form an ion-pair in the capsule. Hydrogen-bonding capabilities of the counter anions also contribute to stabilize host–guest association, because the counter anions trapped within the capsule were in contact with the hydrophilic surfaces of the capsule.