Color tuning and noteworthy photoluminescence quantum yields in crystalline mono-/dinuclear Zn^II complexes

A series of Zn^II complexes with an O,N,O tridentate core is reported. Four species of the general formula ZnLⁱPy₂ were obtained from pyridine, where Lⁱ is a substituted 4-[(aroylhydrazono)methyl]-3-hydroxyphenyl 4-(octyloxy)benzoate group. Crystal structures were solved by single-crystal X-ray diffraction. Nematogenic phase behavior was detected only for the ligands. Photoluminescence spectra were recorded both in solution and in the solid state, and the complexes showed noteworthy photoluminescence in the solid state with wavelengths tunable by varying the aroyl group. Medium to very high photoluminescence quantum yields (PLQY) were recorded on the crystalline complexes obtained in their mononuclear coordination environments. In the case of a 4-nitrobenzoyl substituent on the ligand, a dinuclear complex with formula Zn₂L⁴₂Py₂ showed an unprecedented and exceptionally high PLQY value for a crystalline zinc complex. Molecular and periodic calculations were performed by using Density Functional Theory (DFT).