Thiourea-Based Receptors for Anion Recognition and Signaling

Abstract

This work reports on two thiourea-based receptors with pyridine and amine units including 1-naphthyl (<b>MT1N</b>) and 4-nytrophenyl (<b>MT4N</b>) as signaling units. For both compounds, their affinity and signaling ability toward various anions of different geometry and basicity in DMSO were studied using UV-vis, fluorescence, and ¹H NMR techniques. Anion recognition studies revealed that both <b>MT1N</b> and <b>MT4N</b> have, in general, high affinities toward basic anions. In this regard, a higher acidity of the <b>MT4N</b> receptor was demonstrated. Furthermore, <b>MT4N</b> has a higher affinity for fluoride (log <i>K</i>₁ = 5.98) than for the other anions and can effectively detect it through colorimetric changes that can be monitored by the UV-vis technique. The interaction between receptors and anions mainly involves the hydrogens of the amino and thiourea groups of the former. Complementary single-crystal X-ray diffraction studies and molecular modeling at the DFT level were also performed.