BP23C7: high-yield synthesis and application in constructing [3]rotaxanes and responsive pseudo[2]rotaxanes

Abstract

A biphenyl-23-crown-7 ether (BP23C7) is synthesized in 86% yield from commercially available starting materials. BP23C7 forms pseudo[2]rotaxane with a dibenzylammonium ion (DBA⁺), exhibiting a good association constant value (k_a = 1 × 10³ M⁻¹). Subsequently, fluorophoric properties of BP23C7 and anthracene terminated axles are blended to create responsive pseudo[2]rotaxanes. The “turn-on” fluorescence response of BP23C7 due to the addition of fluoride and chloride anions to pseudo[2]rotaxane systems has been investigated. Concomitant fluorescence quenching of the anthracene moiety of corresponding axles due to ion-pair formation has been addressed. Furthermore, two variants of [23]crown ethers, i.e. BP23C7 and o-xylene-23-crown-7 ether (X23C7), are applied for constructing homo[3]rotaxane architectures. A half-axle comprising of DBA⁺ moiety and a terminal olefin is mixed separately with two [23]crown ethers and subjected to self-metathesis using Grubbs’ first-generation catalyst.