Synthesis, structures and optical properties of a series of zinc(II) complexes bearing salophen ligands derived from 3,5-di-tert-butyl-2-hydroxybenzaldehyde

The photophysical and spectral characteristics of a series of Zn(II)-salophen complexes ZnL1–ZnL6 were systematically analyzed using various analytical techniques. The SC-XRD results of ZnL1 and ZnL4-ZnL6 show that in the crystals of the four complexes, each central metal Zn(II) has a coordination number of five, bonded to the ligand through four donor atoms O^N^N^O and an ethanol molecule. In ethanol at room temperature, all complexes displayed a strong emission at 530–550 nm, characterized by a fluorescence quantum yield of 25–71 % with a significant Stokes shift of 115–129 nm. The complexes fluoresce weaker in the solid state with Φ = 0.4–1.1 % with a red shift in wavelength compared to that in ethanol. The lifetime measured using time-correlated single photon counting showed longer lifetime in solid state (0.37–0.59 ns) than in ethanol (0.14–0.33 ns). Quantum chemical calculations were performed using DFT and TD-DFT methods to obtain structural parameters and the optical properties of complexes.