This invention relates to a triazole based quinoline derivatized calix[4]arene conjugate (L) that serves as a fluorescent sensor for selectively detecting the presence of Fe3+. The conjugate L is employed as a sensitive and selective “switch on” fluorescence receptor for Fe3+ and therefore enables successful discrimination of Fe3+ from Fe2+ ions. Further, conjugate L affords the detection of Fe3+ in nano-molar ranges.