Zinc based organic metal complexes for OLED applications

Zinc-based organic metal complexes have emerged as promising materials for next-generation organic light-emitting diode (OLED) applications due to their unique electronic structure, environmental safety, and cost-effectiveness. Unlike traditional phosphorescent or thermally activated delayed fluorescence (TADF) emitters, Zn(II) complexes operate via ligand-centered (LC) and ligand-to-ligand charge transfer (LLCT) transitions, enabling precise color tuning without relying on heavy metals. These materials have a theoretical internal quantum efficiency cap of 25 %. Yet, they are compatible with solution-based production, thermally stable, easy synthesis, low toxicity, and relatively low-cost production, making them appealing for sustainable optoelectronic technologies. This review systematically examines Zn(II) complexes categorized by emission color, including blue, green, yellow, red, and white. It also highlights the molecular design strategies that influence their photophysical properties and device performance. We emphasize the relationship between molecular structure, electronic behavior, and OLED functionality to guide the rational design of new Zn-based emitters. These insights lay the groundwork for future research into sustainable, high-performance OLED materials, highlighting Zn(II) complexes as a promising route toward scalable, low-toxicity optoelectronic technologies.