Switching the Ion Selectivity from Fe 3+ to Al 3+ by a Triazole‐Appended Calix[4]arene‐Based Amphiphile †

A triazole appended benzaldehydic lower rim derivative of calix[4]arene ( L ) has been synthesized and was thoroughly characterized. In CH 3 CN solution, the L showed greater sensitivity for Fe 3+ by a 5‐fold increase in the absorbance and 37% quenching in the fluorescence intensity, by forming a 1:1 complex. The Fe 3+ induces aggregation in L as studied by microscopy. The Langmuir film formed at the air‐water interface was characterized by pressure‐area isotherm and Brewster angle micrographs, both in the presence and absence of metal ions. The Langmuir films of pure L , { L+ Al 3+ } and { L+ Zn 2+ } were transferred onto H‐terminated Si‐wafer and characterized using Atomic Force Microscopy, contact angle, Grazing Incidence Fourier Transform Infrared Spectrscopy and X‐ray Photoelectron Spectroscopy. The study resulted selective binding of Al 3+ to the Langmuir film of L among the nine metal ions studied. Thus, the calix[4]arene‐conjugate L is sensitive and selective to Fe 3+ in acetonitrile solution whereas to Al 3+ in Langmuir film and hence acts as an ion switch depending upon the physical state of L .