A novel functionalized pillar[5]arene for forming a fluorescent switch and a molecular keypad

We have synthesized a novel functionalized pillar[5]arene (PC5) and used it for fluorescent detection of iron ions (Fe³⁺). It displays a specificity response for iron ions over other common cations (Hg²⁺, Co²⁺, Ca²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Zn²⁺, Cr³⁺, Cu²⁺, Mg²⁺ and Ag⁺) in a solution of DMSO/THF (1:4, v/v). Competitive cations did not show any significant changes in emission intensity and the fluorescence spectra detection limit was 1.25 × 10^-8 M, indicating the high selectivity and sensitivity of the sensor to Fe³⁺. It is well known that H₂PO₄^- has a binding ability with Fe³⁺ to form the complex (Fe(H₂PO₄)₃), so we designed a fluorescent switch and a molecular keypad of PC5 between Fe³⁺ and H₂PO₄^-. Furthermore, a thin film based on the PC5 was prepared, which was confirmed to be a convenient test kit for detecting iron ions.