Cucurbiturils Monofunctionalized on the Methylene Bridge and Their Host‐Guest Properties

Monofunctionalization of cucurbiturils is essential for transferring these potent supramolecular macrocyclic hosts into real‐world application. Here, we present the synthesis of cucurbit[6]urils 1 and 2 in which one methylene bridge is modified by a single substituent containing a nitro or an ammonium group. We investigated host–guest properties in water and 0.2 M NaCl using 1 H NMR and isothermal titration calorimetry, particularly for 2 . The macrocycle 2 self‐associated into dimeric aggregates in pure water, but readily disassembled in the presence of NaCl or organic cations. Cucurbit[7]uril was able to encapsulate the ammonium substituent of 2 inside its cavity resulting in a complex of 1 : 1 stoichiometry with an association constant of 3.1×10 5  M −1 . The presented host–guest properties together with further possible derivatization showcase the potential of cucurbiturils modified in the methylene position such as 1 and 2 for the development of advanced supramolecular systems.