para–Phenylenediamine Dimer as a Redox–Active Guest for Supramolecular Systems

Abstract

Redox‐active components are highly valuable in the construction of molecular devices. We combined two p‐phenylenediamines (p‐PDA) with a biphenyl (BiPhe) unit to prepare a supramolecular guest 4 consisting of three binding sites for cucurbit[7/8]uril (CBn) and/or cyclodextrins (CD). Supramolecular properties of 4 were investigated using NMR, UV‐vis, mass spectrometry and isothermal titration calorimetry. Our analysis revealed that 4 forms higher‐order host–guest complexes, wherein a CD unit occupies the central BiPhe site, secured by two CBn units at the terminal p‐PDA sites. Additionally, 1:1 complexes with α‐CD and β‐CD, a 1:2 complex with γ‐CD and 2:1 complexes with CB7 and CB8 were identified. Through UV‐vis and cyclic voltammetry, redox processes leading to the formation of a stable, deep blue dication diradical of 4 are elucidated. Furthermore, it is demonstrated that CB7 selectively protects oxidised 4 from reduction in the presence of a reducing agent. The supramolecular and redox properties of the structural motif represented by 4 render it an interesting candidate for the construction of supramolecular devices.