Solvent-Dependent Self-Assembly and Aggregation-Induced Emission in Zn(II) Complexes Containing Phenothiazine-Based Terpyridine Ligand and Its Efficacy in Pyrophosphate Sensing

Zn­(II) complexes <b>MTPY–ZnCl</b>_<b>2</b> (<b>C1</b>) and <b>MTPY–Zn­(NO</b>_<b>3</b><b>)</b>_<b>2</b> (<b>C2</b>) based on a new D–A type ligand <b>MTPY</b> involving phenothiazine donor and terpyridine acceptor units have been described. The ligand <b>MTPY</b> and complexes <b>C1</b> and <b>C2</b> display intramolecular charge transfer and substantial solvatochromism. Solid-state emission studies on <b>MTPY</b> further substantiated the occurrence of concentration-induced emission in this molecule. In addition, the complexes <b>C1</b> and <b>C2</b> displayed a solvent-dependent self-assembly which has been examined as a function of the hydrophilic and hydrophobic nature of the solvent systems. The role of hydrophilicity/hydrophobicity of a solvent and compounds on morphology and emission characteristics of the self-assembled aggregates has been investigated by UV–vis, emission, and scanning electron microscopy studies. In addition, it has been categorically shown that aggregation-induced emission in <b>C1</b> offers a simple, sensitive, and rapid means for the detection of pyrophosphates (<b>PPi</b>) in the aqueous medium. Job’s plot analysis suggested a 3:1 binding stoichiometry between <b>C1</b> and <b>PPi</b>, which has been supported by electrospray ionization mass spectrometry and density functional theory. Further, higher affinity of <b>PPi</b> toward <b>C1</b> over <b>C2</b> has also been rationalized by theoretical studies