Calix[4]arene-based fluorescent receptor for selective turn-on detection of Hg²⁺ ions

Abstract

A new fluorescent molecular receptor 3 based on the cone confirmation of calix[4]arene appended with 2-[4-(N,N-dimethylaminophenyl)iminoethoxy] moieties was synthesised, which exhibits selective fluorescence ‘Turn-On’ response in the presence of only Hg²⁺ ions among the various metal ions tested with a detection limit up to the nanomolar range. The fluorescence behaviour of receptor 3 in the presence of Hg²⁺ ions is attributed to the alteration in electronic properties of 3, i.e. working of intramolecular charge transfer (ICT) phenomenon on Hg²⁺ ions complexation. The nitrogen atoms of the imino moieties got involved in the coordination with mercury ions, which enhances the electron-withdrawing ability of imino nitrogen atoms and, hence, leads to an ICT process consequently resulting in the appearance of an emission band at 444 nm.