Realization of Highly Efficient Red Phosphorescence from Bis-Tridentate Iridium(III) Phosphors.

Bis-tridentate Ir(III) metal complexes bring forth interesting photophysical properties, among which the orthogonal arranged, planar tridentate chelates could increase the emission efficiency due to the greater rigidity and, in the meantime, allow strong interligand stacking that could deteriorate the emission efficiency. We bypassed this hurdle by design of five bis-tridentate Ir(III) complexes (-), to which both of their monoanionic ancillary and dianionic chromophoric chelate were functionalized derivative of 2-pyrazolyl-6-phenylpyridine, i.e. pzpyphH parent chelate. Hence, addition of phenyl substituent to the pyrazolyl fragment of pzpyphH gave rise to the precursors of monoanionic chelate (A1H-A3H), on which the additional -butyl and/or methoxy groups were introduced at the selected positions for tuning their steric and electronic properties, while precursors of dianionic chelates was judiciously prepared with an isoquniolinyl central unit on pziqphH in giving the red-shifted emission (cf. L1H and L2H). Factors affected their photophysical properties were discussed by theoretical methods based on DFT and TD-DFT calculation, confirming that the T excited state of all investigated Ir(III) complexes shows a mixed metal-to-ligand charge transfer (MLCT), intraligand charge transfer (ILCT), ligand-to-ligand charge transfer (LLCT), and ligand-centered (LC) transition character. In contrast, the poor quantum yield of is due to the facilitation of the nonradiative decay in comparison to the radiative process. As for potential OLED applications, Ir(III) complex gives superior performance with max. efficiencies of 28.17%, 41.25 cd·A and 37.03 lm·W, CIE = 0.63, 0.37 at 50 mA cm, and small efficiency roll-off.