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Phosphorescent metal emitters that remain stable under OLED (organic light-emitting diode) operating conditions are critical for the commercialization of organic displays and lighting technologies. Until now, only a few non-iridium emitters, including platinum emitters, can meet industry standard requirements for OLED operational lifetime. Here, we report four new tetradentate Pt[O^N^C^N] complexes (Pt1–Pt4) in which the [O^N^C^N] ligand contains peripheral o-diphenylamine or o-carbazole group(s). These o-arylamino groups can (1) increase steric hindrance, inhibit the formation of excimers, and improve efficiency and color purity; (2) cause a fast radiative decay rate, reduce device efficiency roll-off, and extend OLED device operational lifetime. OLEDs with Pt2 as the emitter exhibit an unprecedented long operational lifetime: an LT95 of up to 17 140 h at 1000 cd m−2, which is comparable to that of state-of-the-art iridium emitters. This result is one of the best values reported in the literature for non-iridium-based OLEDs. In addition, a phosphor sensitized fluorescent OLED device was fabricated using Pt2 as the sensitizer, with an EQEmax as high as 30.3% and improved color purity, characterized by a reduction in FWHM to 29 nm and CIE coordinates of (0.29, 0.67). [ABSTRACT FROM AUTHOR]