Blue emissions in organic light-emitting diodes (OLEDs) are essential for their application in solid-state lighting and full-colour flat panel displays. On the other hand, high-power blue emitters are still uncommon, especially those that can achieve the Commission Internationale de l’Eclairage (CIE, X, Y) coordinates of (0.14, 0.08) in the National Television System Committee (NTSC) blue standard and have high external quantum efficiencies (EQE) of more than 5% because their molecular design presents an enormous challenge. Therefore, creating effective, stable, pure, and deep blue fluorescent materials is vital. Here, it is addressed how useful blue fluorescent Zn (II) complexes are for making organic light-emitting diodes (OLEDs). Utilizing Zn (II) complexes is appealing because of their favourable luminous characteristics, acceptance and mobility, and affordability. This mini-review article aims to provide an overview of Zn (II) complexes that emit blue fluorescent light and have been reported since 2018, while highlighting the unique qualities that make them appropriate OLED materials.

We present here the design, synthesis, and photophysical properties of two novel fluorescent zinc (II) complexes, ZnCl₂(ImL1)₂ and ZnCl₂(ImL2)₂, containing 4-(1-octyl-1H-imidazol-4-yl)-N,N-diphenyl-[1,1-biphenyl]-4-yl)-4-amine ImL1 and 9-(4-(1-octyl-1H-imidazol-4-yl)-[1,1-biphenyl]-4-yl)-9H-carbazole ImL2 ligands. The newly synthesized free ligands and their zinc (II) complexes were characterized using several spectroscopic techniques; their structures were identified by single-crystal X-ray diffraction; and their photophysical properties have been studied in the context of their chemical structure. The ZnCl₂(ImL1)₂ and ZnCl₂(ImL2)₂ complexes showed good thermal stability at 341 °C and 365 °C, respectively. Photophysical properties, including UV-Vis absorption spectra in ethanol solution and photoluminescence (PL) in both solid state and ethanol solution, were determined. UV-Vis adsorption data indicated that both free ligands had similar UV-Vis absorption properties, while their Zn (II) complexes had distinctive absorption characteristics. The fluorescence spectra show that both ligands and their corresponding Zn (II) complexes emit violet to cyan luminescence in the solid state at room temperature, while in ethanol solution at the same temperature, they exhibit efficient photoluminescence properties in the UV-A emission spectral region. Because of these photophysical properties, the synthesized ligands and their cognate Zn (II) complexes can be used as scaffolds for the potential development of optoelectronic materials.

The synthesis of the title compound, [Zn(C₄H₆N₂)₆](NO₃)₂, is described. This complex consists of a central zinc metal ion surrounded by six 1-methylimidazole ligands, charge balanced by two nitrate anions. The complex crystallizes in the space group P\overline{3}. In the crystal, the nitrate ions are situated within the cavities created by the [Zn(N-Melm)₆]²⁺ cations, serving as counter-ions. The three oxygen atoms of the nitrate ion engage in weak C—H...O interactions. In addition to single-crystal X-ray diffraction analysis, the complex was characterized using elemental analysis, ¹H NMR, ¹³C NMR, and FTIR spectroscopy.

The title complex salt, [Zn(C ₉ H ₈ N ₂ ) ₄ ](NO ₃ ) ₂ , features a central zinc(II) ion coordinated by four 5-phenylimidazole ligands, with two nitrate anions providing charge balance. It crystallizes in the monoclinic space group C2/c . In the crystal, the nitrate ions occupy the voids formed by the [Zn(C ₉ H ₈ N ₂ ) ₄ ] ²⁺ cations and function as counter-ions. The nitrate oxygen atoms participate in strong N—H...O hydrogen-bonding interactions. The crystal studied was refined as a two-component twin.