Ternary ambipolar phosphine oxide hosts based on indirect linkage for highly efficient blue electrophosphorescence: towards high triplet energy, low driving voltage and stable efficiencies.

The effective strategy of indirect linakge for constructing ternary ambipolar phosphine oxide (PO) hosts with the high first triplet energy levels (T(1)) was successfully demonstrated. The interplay between the chromophore, hole and electron transporting moieties was effectively restrained. Both of T(1) as high as 3.0 eV and ambipolar characteristics were perfectly realized, which consequently resulted in the highly efficient blue-emitting phosphorescent organic light-emitting diodes with low driving voltage and stable efficiencies.