A new 1,3-di-capped calix[4]arene conjugate of salicylidene (L) has been synthesized, characterized and the structure has been established by single crystal XRD. L shows selectivity towards Hg 2+ in ethanol by turn-on fluorescence among the biologically important metal ions studied. The species of recognition has been modeled by DFT computational calculations to result in conformational changes in the arms that support the turn-on fluorescence behaviour. © 2011 The Royal Society of Chemistry.