A new coumarin-derived imine dFont">IC1 was designed for highly selective sensing of Zn2+ over Cd2+ ions in aqueous solution based on a controllable CN isomerization mechanism. Methyl as a fine controllable unit was incorporated into dFont">IC1 to tune the conformational change of imine and thus significantly improve its selectivity to Zn2+ compared with methyl-free imine dFont">IC2. Sensor dFont">IC1 was also utilized to image intracellular Zn2+ ions in HepG2 cells with a good performance.