Logic Operations at the Molecular Level. An XOR Gate Based on a Molecular Machine

A pseudorotaxane formed in solution by self-assembly of a wire-type electron acceptor (2,7-dibenzyldiazapyrenium dication) and a macrocyclic electron donor (2,3-dinaphtho-30-crown-10) can be unthreaded and rethreaded by chemical inputs. Unthreading can be obtained by addition of stoichiometric amounts of acids or amines. After the unthreading process caused by addition of acid, rethreading can be obtained by addition of amine, and vice versa. The threading/unthreading processes are accompanied (and therefore can be monitored) by strong changes in the fluorescence properties of the system. The input (chemical)/output (fluorescence) characteristics of this molecular-level system correspond to those of an XOR logic gate.