Blue luminescent Zn(II) AND Cd(II) bis{N-[2-((E)-allyliminomethyl)phenyl]-4-methylbenzenesulfonamidate} complexes: Structural diversity and application of the Zn(II) emitter in OLEDS

Abstract

New Zn(II) and Cd(II) complexes based on N-[2-((E)-allyliminomethyl)phenyl]-4-methylbenzenesulfonamide (HL) were synthesized. The structure and composition of the azomethine and the coordination compounds were established by elemental analysis, IR and ¹H NMR spectroscopy. The molecular and crystal structures of the Zn(II) and Cd(II) complexes were determined by single-crystal X-ray diffraction analysis. Both complexes were found to crystallize in the monoclinic system (space group P2₁/n) and they are isostructural. The coordination environment of the metal ion is significantly different in the complexes: Zn(II) adopts a distorted tetrahedral geometry, whereas Cd(II) exhibits a tendency to increase its coordination number, forming two additional weak bonds with oxygen atoms of sulfonyl groups. The photophysical properties of the ligand and the complexes were investigated in CH₂Cl₂ solution and in the solid state. In the solid state, intense blue luminescence is observed, with emission maxima at 449 and 448 nm in the Zn(II) and Cd(II) complexes, respectively. The zinc(II) complex exhibits a high absolute quantum yield (26.3%), significantly exceeding that of the cadmium(II) counterpart (15.8%). Due to its high thermal stability and efficient blue emission, the zinc complex was used as an emitter in an OLED device. A maximum brightness of 1030 cd/m² and an external quantum efficiency of 2.58% were achieved.