Manipulating charge-transfer character with electron-withdrawing main-group moieties for the color tuning of iridium electrophosphors

A new and synthetically versatile strategy has been developed for the phosphorescence color tuning of cyclometalated iridium phosphors by simple tailoring of the phenyl ring of ppy (Hppy=2-phenylpyridine) with various main-group moieties in [Ir(ppy-X)(2)(acac)] (X=B(Mes)(2), SiPh3, GePh3, NPh2, POPh2, OPh, SPh, SO2Ph). This can be achieved by shifting the charge-transfer character from the pyridyl groups in some traditional iridium ppy-type complexes to the electron-withdrawing main-group moieties and these assignments were supported by theoretical calculations. This new color tuning strategy in Ir-III-based triplet emitters using electron-withdrawing main-group moieties provides access to Ir-III phosphors with improved electron injection/electron transporting features essential for highly efficient, color-switchable organic light-emitting diodes (OLEDs). The present work furnished OLED colors spanning from bluish-green to red (505-609 nm) with high electroluminescence efficiencies which have great potential for application in multicolor displays. The maximum external quantum efficiency of 9.4%, luminance efficiency of 10.3 cd A(-1) and power efficiency of 5.0 lm W-1 for the red OLED (X = B(Mes)(2)), 11.1%, 35.0 cd A(-1), and 26.8 lm W-1 for the bluish-green device (X=OPh), 10.3%, 36.9 cd A(-1), and 28.6 lm W-1 for the bright green device (X = NPh2) as well as 10.7%, 35.1 cd A(-1), and 23.1 lm W-1 for the yellow-emitting device (X = SO2Ph) can be obtained.