Chromene “Lock”, Thiol “Key”, and Mercury(II) Ion “Hand”: A Single Molecular Machine Recognition System

A regenerative, molecular machine-like “ON−OFF−ON” chemosensor based on a chromene molecule with the pyran ring “OFF−ON−OFF” cycle is reported for the first time. It behaves as a molecular lock that requires a thiol “key” to open the lock and a mercury(II) ion “hand” that unlatches the key for unsheathing the key to close the lock.