Catalytic electron drives host-guest recognition.

Electron injection is demonstrated to trigger electrocatalytic chain reactions capable of releasing a solvent molecule and forming a redox active guest molecule. One-electron reduction of a hydroxy anthrone derivative (AQH-CH 2 CN) results in the formation of an anthraquinone radical anion (AQ˙ - ) and acetonitrile (CH 3 CN). The resulting fragment of AQ˙ - exhibits high stability under mild reducing conditions, and it has enough reducing power to reduce the reactant of AQH-CH 2 CN. Hence, subsequent electron transfer from AQ˙ - to AQH-CH 2 CN yields the secondary AQ˙ - and CH 3 CN, while the initial AQ˙ - is subsequently oxidized to AQ. Overall, the reactants of AQH-CH 2 CN are completely converted into AQ and CH 3 CN in sustainable electrocatalytic chain reactions. These electrocatalytic chain reactions are mild and sustainable, successfully achieving catalytic electron-triggered charge-transfer (CT) complex formation. Reactant AQH-CH 2 CN is non-planar, making it unsuitable for CT interaction with an electron donor host compound (U H Ant 2 ) bearing parallel anthracene tweezers. However, conversion of AQH-CH 2 CN to planar electron acceptor AQ by the electrocatalytic chain reactions turns on CT interaction, generating a host CT complex with U H Ant 2 (AQ ⊂ U H Ant 2 ). Therefore, sustainable electrocatalytic chain reactions can control CT interactions using only a catalytic amount of electrons, ultimately affording a one-electron switch associated with catalytic electron-triggered turn-on molecular recognition.