N‐Substituted Acridinium as a Multi‐Responsive Recognition Unit in Supramolecular Chemistry

The N‐substituted acridinium motif is an electron‐deficient unit with appealing multi‐responsive properties which have been exploited in the field of supramolecular chemistry. This building block reversibly alters its shape, with its chemical and optical properties in response to a chemical or redox signal. In this Review, we discuss selected examples where the switchable properties of 9‐aryl‐N‐methyl‐acridinium lead to actuators, multi‐input and multi‐output systems, host or guest systems, and to interlocked systems with controllable motion. Highly versatile: N‐substituted acridinium moieties are emerging building blocks in supramolecular systems on account of their unique multi‐responsive properties. This Review introduces the physico‐chemical properties of the N‐substituted acridinium unit, and highlights some examples of use i) as a molecular guest, ii) as an active unit in molecular hosts, and iii) in mechanically interlocked molecules.