Tridentate chelating ligand based fluorescent Zn(ii) coordination compounds for highly selective detection of picric acid

Abstract

In this work we report two zinc(II) complexes, namely {[Zn(L)(dca)](0.5CH₃OH)}_n (1) and [Zn₂(L)₂(N₃)₂] (2), (where HL = 1-((2-pyridylmethyl)iminomethyl)-2-naphthol, dca = dicyanoamide anion) that have been structurally characterized by spectroscopic technique and X-ray single crystal diffraction. Structural analysis showed for complex 1 an undulated polymer with Zn(L) units connected by bridging dca anions, while 2 is a dinuclear complex where the azide anions are monodentate and end-on coordinated. The emission properties of both complexes have been studied in various organic solvents, and among them, nitrobenzene attracts attention due to its significant quenched effect. The synthesized complexes were tested as fluorescence-based sensors for nitroaromatic analytes (nitrobenzene, 4-nitrotoluene, 2,4-dinitrophenol, p-nitrophenol, 1,3-dinitrobenzene, 2-nitrotoluene, 4-nitrobenzaldehyde, and picric acid) and results showed that complexes 1 and 2 exhibit a selective response in particular towards picric acid (PA). The fluorescence sensor mechanisms have been explained according to photoinduced electron transfer (PET) mechanism and resonance energy transfer (RET).