Two new calix[4]arene based fluorescence sensors (L1 and L2) have been synthesized and characterized. L1 was found to selectively quench fluorescence intensity upon addition of Cu²⁺ ions through host–guest complexation and display “on–off” behavior while L2 was not that efficient. The in situ generated L1·Cu²⁺ complex could further recognize CN⁻ from the anionic broth with a distinct “off–on” behavior in the fluorescence titration.