Redox-Responsive Macrocyclic Hosts Based on Calix[4]arene and Calix[4]resorcinarene Scaffolds

Calix[4]arenes and calix[4]resorcinarenes are well-known macrocyclic hosts that can be tailored to bind guests of very different natures, including anions, cations, and various neutral molecules. The molecular architectures of the hosts can be altered in many ways: by attaching polar or hydrophilic groups, extending inner cavities with enlarged aromatic side walls, and adding H-bonding sites to promote the formation of molecular capsules. The attachment of different types of redox-active moieties renders calix[4]arene and calix[4]resorcinarene derivatives electrochemically active, enabling them to either control the guest-binding properties of the receptors or be used as electrochemical sensors. This review will focus on calix[4]arene and calix[4]resorcinarene macrocyclic hosts with appended redox-active groups, such as ferrocene, tetrathiafulvalene, and quinone. We will discuss molecular receptors that can serve as redox sensors for cations or electron-deficient molecules or can bind and release their guests controlled by redox or electrochemical stimuli.