Chromogenic sensors based on calix[4]pyrrole-strapped calix[4]arene

Abstract

A new chromogenic sensor 1,3-di-p-nitrophenylazo-calix[4]arene-calix[4]pyrrole (9) was successfully synthesized and characterized by spectroscopic methodes. Anion binding abilities of ligand 9 was studied by UV-vis spectrophotometry and their color changes. Ligand 9 was found to bind F-, AcO-, BzO- and H2PO4- to a different extent which ascribed to the internal charge transfer occurred upon deprotonation by anions. Then ligand 9 could be discriminate F-, AcO-, BzO- and H2PO4- which have same basicity but different in their sizes and shapes. Ligand 9 also showed highly selective binding with Ca2+ using azocalix[4]crownether as a metal chelating unit. Ligand 9 has shown no binding situation with the ion-pair CaF2 by using 1H-NMR spectroscopy. A series of F-, AcO-, BzO- and H2PO4- were titrated into the solution of complex 9 Ca2+ to study ion pair binding properties of ligand 9. In case of, AcO- and BzO- were found to induce a bathochromic shift in the spectrum of complex 9Ca2+ but F- and H2PO4- gave back the spectrum of the free ligand 9. 1,3-Di-p-nitrophenylazo-calix[4]diacetophenone (7) which was lack of the calix[4]pyrrole unit was used to compare the binding abilities with ligand 9. Ligand 7 showed no internal charge transfer upon complexing with anions and gave different ion-pair binding as compared to ligand 9.