Switching the Ion Selectivity from Fe3+ to Al3+ by a Triazole‐Appended Calix[4]arene‐Based Amphiphile

• Published in: ChemistrySelect (Weinheim) 2018-01, Vol.3 (4), p.1248-1256
• Main Authors: Nag, Rahul, Vashishtha, Manu, Rao, Chebrolu Pulla
• Format: Article
• Language: English
• Subjects: Air-water interface; Calixarenes; Ion sensing; Langmuir-Blodgett film; Pressure-area isotherm
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.201702999

A triazole appended benzaldehydic lower rim derivative of calix[4]arene (L) has been synthesized and was thoroughly characterized. In CH3CN solution, the L showed greater sensitivity for Fe3+ by a 5‐fold increase in the absorbance and 37% quenching in the fluorescence intensity, by forming a 1:1 complex. The Fe3+ 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+Al3+} and {L+Zn2+} 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 Al3+ to the Langmuir film of L among the nine metal ions studied. Thus, the calix[4]arene‐conjugate L is sensitive and selective to Fe3+ in acetonitrile solution whereas to Al3+ in Langmuir film and hence acts as an ion switch depending upon the physical state of L. A triazole appended benzaldehydic lower rim derivative of amphiphilic calix[4]arene(L) has been synthesized. The selectivity of L towards a series of metal ions has been shown through various spectroscopic and microscopic studies in solution and at the air‐water interface. It has been observed that L acts as a metal ion sensor and the sensing switches from Fe3+ → Al3+ on going from acetonitrile solution to the air‐water interface i. e., Langmuir film.