Control of Photoisomerization of an Azoazacryptand by Anion Binding and Cucurbit[8]uril Encapsulation in an Aqueous Solution

Control of a receptor isomerization bearing multiple light-switchable subunits in a confined space is critical for the design of synthetic molecular machines. Towards this goal, a new azacryptand containing three azobenzene subunits has been developed and its photoisomerization in aqueous solution has been studied depending on anion coordination and recognition by a larger host - cucurbit[8]uril. The cryptand in its hexaprotonated form shows considerable affinity for fluoride and perchlorate, which in turn affects the isomer distribution of the receptor under UV-light irradiations stabilizing isomers of the cryptand with Z-configurations. Cucurbit[8]uril (CB[8]) was found to be able to encapsulate isomers of the cryptand by forming a Matryoshka-type complex . The irradiation of a 10:1 CB[8] - cryptand mixture has led to a selective conversion of the cryptand to the E,E,Z isomer inside CB[8]. It has been demonstrated that the addition of fluoride to the resulted complex induces a release of the cryptand as a major E,E,E isomer, while other studied anions were ineffective in this reaction. To our knowledge, this work presents a first example of a host-controlled photoisomerization of an anion receptor bearing multiple switching azobenzenes and model the function of naturally occurring chaperones.