Time Programmable Locking/Unlocking of the Calix[4]arene Scaffold by Means of Chemical Fuels

In this work, we report that 2-cyano-2-phenylpropanoic acid and itsp-Cl,p-CH(3)andp-OCH(3)derivatives can be used as chemical fuels to control the geometry of the calix[4]arene scaffold in its cone conformation. It is shown that, under the action of the fuel, the cone calix[4]arene platform assumes a locked shape with two opposite aromatic rings strongly convergent and the other two strongly divergent (pinched cone conformation). Only when the fuel is exhausted, the cone calix[4]arene scaffold returns to its resting, unlocked shape. Remarkably, the duration of the locked state can be controlled at will by varying the fuel structure or amount. A kinetic study of the process shows that the consume of the fuel is catalyzed by the unlocked calixarene that behaves as an autocatalyst for its own production. A mechanism is proposed for the reaction of fuel consumption.