Azobenzene-based system for fluorimetric sensing of H(2)PO(4)(-) (Pi) that works as a molecular keypad lock.

A 'novel' and cost-effective 'on-off'-type monophosphate H(2)PO(4)(-) (Pi) chemosensor based on the mononuclear 2,2'-dihydroxyazobenzene (DHAB)-Zn(ii) complex was developed and a molecular keypad lock can be realized in the DHAB-based system by using Zn(ii) cations and Pi anions as inputs.