Novel Ambipolar Orthogonal Donor–Acceptor Host for Blue Organic Light Emitting Diodes

Ambipolar triplet hosts comprising 1,2,4-triazole and carbazole in ortho-positions have been developed. The blue PHOLED has a high current efficiency of 47.1 cd A–1, power efficiency of 41.2 lm W–1, and low efficiency roll-off. The high efficiency was attributed to the successful control of π-conjugation through orthogonal arrangement of the substituents so that a wide T1–S0 gap could be maintained.