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A new series of phosphorescent platinum(II) cyclometalated complexes with distinct electronic structures has been developed by simple tailoring of the phenyl ring of ppy (Hppy = 2-phenylpyridine) with various main-group moieties in Pt(ppy-X)(acac) (X = B(Mes)2, SiPh3, GePh3, NPh2, POPh2, OPh, SPh, SO2Ph substituted at the para position). Their distinctive electronic characters, resulting in improved hole-injection/hole-transporting or electron-injection/electron-transporting features, have confined/consumed the electrons in the emission layer of organic light-emitting diodes (OLEDs) to achieve good color purity and high efficiency of the devices. The maximum external quantum efficiency of 9.52%, luminance efficiency of 30.00 cd A−1 and power efficiency of 8.36 lm W−1 for the OLEDs with Pt-B (X = B(Mes)2) as the emitter, 8.50%, 29.74 cd A−1 and 19.73 lm W−1 for the device with Pt-N (X = NPh2), 7.92%, 22.06 cd A−1 and 13.64 lm W−1 for the device with Pt-PO (X = POPh2) as well as 8.35%, 19.59 cd A−1 and 7.83 lm W−1 for the device with Pt-SO2 (X = SO2Ph) can be obtained. By taking advantage of the unique electronic structures of the Pt-Ge (X = GePh3) and Pt-O (X = OPh) green emitters and the intrinsic property of blue-emitting hole-transport layer of 4,4′-bisN-(1-naphthyl)-N-phenylaminobiphenyl (NPB), single-dopant white OLEDs (WOLEDs) can be developed. These simple WOLEDs emit white light of very high quality (CIE at (0.354, 0.360), CRI of ca. 97 and CCT at 4719 K) even at high brightness (>15000 cd m−2) and the present work represents significant progress to address the bottle-neck problem of WOLEDs for the efficiency/color quality/brightness trade-off optimization that is necessary for pure white light of great commercial value.
Zhou et al. (Fri,) studied this question.