Synthesis, characterization and ion recognition studies of lower rim 1,3-di{rhodamine} conjugate of calix[4]arene

An amido-linked rhodamine conjugate of calix[4]arene, L has been synthesized and characterized. Metal ion recognition properties of L have been studied by emission and absorption techniques with 14 different metal ions including the transition ones. Results show that, L exhibits ratiometric emission intensity towards Hg2+, Fe2+, Fe3+, Cu2+, Pb2+ and Zn2+. Composition of the complex formed in the solution has been found to be 1:2 (L:Mn+), based on the Job's plot. The L can also act as a chemosensor for Hg2+ through naked eye detection. Fluorescence quenching observed at 485 nm follows an order, Hg2+ >> Fe3+ similar to Cu2+ > Zn2+ > Pb2+ > Ca2+, while the enhancement observed at 580 nm follows, Hg2+ >> Fe2+ similar to Pb2+ > Zn2+. Mode of interaction of Mn+ with L is by the ring opening of spirolactam moiety