A Molecular Lock with Hydrogen Sulfate as “Key” and Fluoride as “Hand”: Computing Based Insights on the Functioning Mechanism

Abstract The present work demonstrates a new fully regenerative, molecular machine‐like “ON‐OFF‐ON” chemosensor based on a β‐carboline molecule “OFF‐ON‐OFF” cycle. It behaves as a molecular lock that requires a hydrogen sulfate (HSO 4 − ) ion as “key” to open the lock and a fluoride (F − ) ion as “hand” that removes the key from the lock to close the lock. The reversibility and reusability of sensor for the detection of hydrogen sulfate and fluoride ions were tested for six cycles. Experimental and computational studies reveal that the proton transfer process from hydrogen sulfate (HSO 4 − ) ion to the pyridinic nitrogen atom of norharmane leading to the formation of a hydrogen bonded ion pair (HBIP) provides the optical changes in the visible region that are advantageous for real time and on‐site application.