**4. Conclusions**

Substantial room for innovation remains in OLED materials research, and the development of robust, high efficiency emitters for diverse applications remains a challenge both in academia and industry. While in the past decade, tris-(bidentate chelate) iridium(III) complexes have been seemingly edging out other classes of metal phosphors, it is remarkable that tetradentate platinum(II) emitters have demonstrated high performance and are being increasingly recognized by academia and industry as a competitive alternative. Importantly, the unique aggregation behavior and the associated photophysical properties afforded by their planar coordiantion geometry distinguish platinum(II) emitters from octahedral iridium(III) emitters. The unique photophysical properties of platinum(II) emitters render them well suited for some OLED applications using simple device structures such single-dopant WOLEDs and aggregation-based red and NIR OLEDs as covered in this review. In addition, appropriate molecular design of the ligand scaffold allows the regulation of the emissive excited states and the intermolecular interactions, which consequently offers flexibility in manipulating the emission characteristics of platinum(II) emitters to cater to various OLED applications. Indeed, sustained and concerted efforts between academia and industry have already realized successful application of tetradentate Pt(II) emitters in OLED devices in an industrial setting. It is without doubt that Pt(II) emitters, after full optimization, will meet the technical specifications including operational stability, required for commercialization. We hope the perspective described herein will spur interest among stakeholders and drive further development of tetradentate Pt(II) emitters for display and lighting applications.
