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 MTPY-ZnCl2 (C1) and MTPY Zn(NO3)(2) (C2) based on a new D-A type ligand MTPY involving phenothiazine donor and terpyridine acceptor units have been described. The ligand MTPY and complexes Cl and C2 display intramolecular charge transfer and substantial solvatochromism. Solid-state emission studies on MTPY further substantiated the occurrence of concentration-induced emission in this molecule. In addition, the complexes C1 and C2 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 Cl offers a simple, sensitive, and rapid means for the detection of pyrophosphates (PPi) in the aqueous medium. Job's plot analysis suggested a 3:1 binding stoichiometry between Cl and PPi, which has been supported by electrospray ionization mass spectrometry and density functional theory. Further, higher affinity of PPi toward Cl over C2 has also been rationalized by theoretical studies.