Synthesis, structure, photo- and electroluminescent properties of methyl- and alkoxy-substituted 4-methyl-N-[2-(phenyliminomethyl)phenyl]benzenesulfamides and their zinc(II) complexes

A series of novel Zn(II) bischelate complexes based on azomethines of 2-(N-tosylamino)benzaldehyde and aromatic amines (aniline, 4-methylaniline, 4-methoxyaniline, 2-methoxylaniline, and 4-ethoxylanine) were designed and synthesized with the aim of studying their photo- and electro-luminescent properties. The structures of the synthesized azomethines and their complexes were studied by elemental analysis, infrared (IR) and proton nuclear magnetic resonance (¹H NMR) spectroscopy. The structure of the Zn(II)-complexes was determined using X-ray diffraction analysis. In the solid state, azomethines exhibit bright luminescence in the yellow part of the spectrum with high emission efficiency and quantum yields of approximately 50 %. Zinc complexes based on them exhibit noticeable luminescence in the solid state and in solutions of methylene chloride. Compared to azomethines, the luminescence maxima of Zn(II) complexes are hypsochromically shifted, and they exhibit pronounced blue-green luminescence. The OLED devices based on zinc(II) complexes emit strong bluish-green light with a peak maximum at 478–490 nm. The device with the best parameters has a maximum luminance of 2103 cd/m², a current efficiency of 14.0 cd/A, and an overall efficiency of 4.8 %, with a turn-on voltage of 3.6 V.