Series of O,N,O-tridentate ligands zinc(II) complexes with high solid-state photoluminescence quantum yield

Four neutral complexes were synthesized by reaction of tridentate N-salicylidene-N′-aroylhydrazine ligands with zinc(II) acetate and pyridine as a further ligand. The O,N,O-chelating molecules N-4- [octyloxy(phenoxy)]salicylidene-N′-fluorobenzoylhydrazine (L¹), N-4-[octyloxy(phenoxy)]salicylidene-N′-(benzothiazolyl)hydrazine (L ²), N-4-[octyloxy(phenoxy)]salicylidene-N′- cyanobenzoylhydrazine (L³), and N-4-[octyloxy(phenoxy)]salicylidene- N′-nitrobenzoylhydrazine (L⁴) gave dinuclear O-bridged complexes Zn₂Lⁱ₂Py_2n (n = 1 or 2 in a special case). The ligands and complexes were characterized by mass spectrometry and ¹H NMR, UV/Vis, photoluminescence (PL), and FTIR spectroscopy. The structures of the complexes were solved by single-crystal X-ray analysis. Nematogenic phase behavior was detected for some ligands by thermogravimetric analysis/differential scanning calorimetry (TGA-DSC) and optical observations. The solution and solid-state photoluminescence spectra were recorded and show that the ligands are roughly nonfluorescent, whereas all of the complexes show noteworthy emission in widely different spectral regions. The photoluminescence maxima of the complexes in the solid state are dependent on the acceptor group, and medium-to-high PL quantum yields were recorded for all of the crystalline complexes. Both periodic and molecular DFT calculations were performed to rationalize the absorbance of these complexes at the "one-particle" level.