Switching around two axles: controlling the configuration and conformation of a hydrazone-based switch

A hydrazone-based rotary switch, having a quinolinyl stator and a pyridine ring as part of the rotor, can be induced using pH to undergo a four-step switching sequence. This process yields three stable isomers and a fourth "metastable" one that can all be addressed separately based on the sequence of acid and base added. The switching process proceeds via conformational and/or configurational changes, allowing the molecule to rotate around two different axles.