Synthesis, structure, photophysical properties and DFT investigation of novel Zn(II) complexes bearing π-extended 8-hydroxyquinoline-derived ligands

Abstract

Six new Zn(II) complexes (Zn1–Zn6) were synthesized from 2,4-diaryl-8-hydroxyquinoline derivatives (HQ1–HQ6) and structurally characterized by ESI-MS, 1H NMR spectra and SC XRD. The analysis of NMR and XRD results revealed that all the complex geometries are tetrahedral in which the ligands coordinated with Zn(II) via the N and O atoms. The investigation of photophysical properties showed that the ligands themself are non-fluorescent, while the complexes displayed a strong emission at 597–628 nm, characterized by a fluorescence quantum yield of 0.36–0.98 with a large Stokes shift of 174–202 nm, except complex Zn2. Notably, the quantum yields of the complexes in the solvents and emission intensity in the solid state tend to increase in the presence of electron-donating substituents. Quantum chemical computations were conducted to investigate the electronic structure and optical characteristics of the compounds, yielding outcomes consistent with experimental observations.