Ricerc@Sapienza

Back and forth motions of the acid–base-operated molecular switch 1 are photo-controlled by irradiation of a solution, which also contains the photolabile pre-fuel 4. The photo-stimulated deprotection of the pre-fuel produces controlled amounts of acid 2, the base-promoted decarboxylation of which fuels the back and forth motions of the Sauvage-type [2]-catenane-based molecular switch. Because switch 1 and pre-fuel 4 do not interact in the absence of irradiation, an excess of the latter with respect to 1 can be added to the solution from the beginning.

We report on catalysis by a fuel-induced transient state of a synthetic molecular machine. A [2]rotaxane molecular shuttle containing secondary ammonium/amine and thiourea stations is converted between catalytically inactive and active states by pulses of a chemical fuel (trichloroacetic acid), which is itself decomposed by the machine and/or the presence of additional base. The ON-state of the rotaxane catalyzes the reduction of a nitrostyrene by transfer hydrogenation.

Natural molecular machines require a continuous fuel supply to perform motions and/or remain in a functional state. Consequently, the aim of developing artificial devices and materials with life-type properties has motivated a growing interest in abiotic chemical fuels and in their supply modalities. Many artificial molecular machines have been developed in which the sequential addition of several chemical reagents allows the machine to perform complete cycles of motion.