An idealized bipolar host material and dopant are synthesized for deep-red phosphorescent organic light-emitting diodes (PhOLEDs). The host material exhibits a low-lying lowest unoccupied molecular orbital and high thermal and morphological stability, while the dopant emits sharply at 616 nm with a full width at half-maximum of only 39 nm. The new host/guest combination for the deep-red device yields the highest device efficiencies to date.