Electrochemical and optical anion sensors based on calix[4]arene crown ether

Abstract

A new heteroditopic receptor derived from calix[4]arene crown ether in 1,3-alternate conformation with amidoferrocene as a signaling unit, receptor L1, was synthesized and its anion binding properties with the analogous receptor L2 were compared. It was found that the presence of cations alter anion binding abilities. Complexation studies using 1H NMR titration found that the complex of [L2Na+] gave more selectivity with AcO- and Br- ions, whereas [L1Na+] showed higher binding constants with all anions in 5% v/v of CD3CN in CDCl3. In addition, only oxidized form of [L2Na+] detected Cl- and AcO- in 40% v/v of CH3CN in CH2Cl2 to more cathodically shifts compared to its normal form. Two heteroditopic dual sensors based on calix[4]arene crown ether containing amidoanthraquinone pendants in cone and 1,3-alternate conformations (receptors L3 and L4, respectively) were synthesized. Both receptors exhibited dual sensing modes through photophysical and electrochemical properties. Receptors L3 and L4 can sense F- photophysically in dried CH3CN and H2PO4- electrochemically in 40% CH3CN/CH2Cl2. Interestingly, in the presence of K+, receptor L3 showed higher sensitivity with F- via the higher fluorescence intensity at 520 nm and the higher binding constants, while this phenomenon was not observed in the case of receptor L4. In addition, only receptor L3 gave remarkably potential shifts in its redox wave II upon adding F- and AcO- in the presence of K+. According to these studies, the cooperative effects were controlled by not only the additional electrostatic forces but also the topology of the receptor molecules.