Efficient deep-blue-emitting tetradentate platinum complexes with a narrow spectral bandwidth are presented, which demonstrate CIEx ≈ 0.15 and CIEy < 0.1. Ultimately, an organic light-emitting diode (OLED) with 24.8% peak external quantum efficiency and CIE coordinates of (0.147, 0.079) is fabricated using PtON7-dtb.

Phosphorescent organic light-emitting diodes (OLEDs) are leading candidates for next-generation displays and solid-state lighting technologies. Much of the academic and commercial pursuits in phosphorescent OLEDs have been dominated by Ir(III) complexes. Over the past decade recent developments have enabled square planar Pt(II) and Pd(II) complexes to meet or exceed the performance of Ir complexes in many aspects. In particular, the development of N-heterocyclic carbene-based emitters and tetradentate cyclometalated Pt and Pd complexes have significantly improved the emission efficiency and reduced their radiative lifetimes making them competitive with the best reported Ir complexes. Furthermore, their unique and diverse molecular design possibilities have enabled exciting photophysical attributes including narrower emission spectra, excimer -based white emission, and thermally activated delayed fluorescence. These developments have enabled the fabrication of efficient and "pure" blue OLEDs, single-doped white devices with EQEs of over 25% and high CRI, and device operational lifetimes which show early promise that square planar metal complexes can be stable enough for commercialization. These accomplishments have brought Pt complexes to the forefront of academic research. The molecular design strategies, photophysical characteristics, and device performance resulting from the major advancements in emissive Pt and Pd square planar complexes are discussed.

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In order to develop organic light-emitting diodes with improved optical properties, a series of phosphorescent complexes exhibiting narrow-band emission spectra are prepared and color tuned to emit efficiently across the whole visible spectrum through a judicious molecular design. Devices employing a green narrow-band phosphorescent emitter are fabricated and demonstrate an internal quantum efficiency of close to unity and impressive device operational lifetimes, estimate at over 70,000 hours at a practical luminance of 100 cd/m 2 . Additionally a deep blue narrow-band emitter is incorporated into a device setting which demonstrates a peak external quantum efficiency of 17.6% and CIE coordinates of (0.14, 0.09).

Using a single tetradentate platinum emitter dubbed Pt7O7, efficient and stable white organic light-emitting diodes are developed. The excimer-based white devices achieve an external quantum efficiency (EQE) of 24.5%, coordinates of (0.37, 0.42) based on the Commission internationale de l'éclairage (CIE) system, and a color rendering index (CRI) of 70. Moreover, devices of Pt7O7 in a stable structure demonstrate operational lifetimes (50% initial luminance) of 36 h at an elevated driving current of 20 mA cm2, which corresponds to over 10,000 h at 100 cd m2.