Deep Blue Emitter Based on Tris(triazolo)triazine Moiety with CIE_y < 0.08 for Highly Efficient Solution-Processed Organic Light-Emitting Diodes Via Molecular Strategy of “Hot Excitons”

Realizing high efficiency deep blue emission with a Commission international de I'Eclairage (CIE) coordinate of CIE_y < 0.08 is still a big challenge. In this contribution, three molecules, named TTT-TPA-R (R = H, OMe, ^tBu), using tris(triazolo)triazine (TTT) as the acceptor and triphenylamine derivatives (TPA-R, R = H, OMe, and ^tBu) as the donor are prepared and characterized. All these emitters show deep/pure blue emission between 420 and 470 nm in the PMMA film, concomitant with the excellent emission efficiency of 80–100%. Both experimental and calculated methods demonstrate that these emitters exhibit a clearly hybridized local and charge-transfer excited state and can harvest both singlet and triplet excitons via reverse intersystem crossing process from the high-lying triplet to singlet states. Therefore, the solution processable deep blue organic light-emitting diodes (OLEDs) achieve a maximum external quantum efficiency (EQE_max) of 10.5% which is the recorded value for the solution processable deep blue OLED based on the “hot exciton” mechanism. Using TTT-TPA-H as the host material, solution-processed phosphorescent OLED based on PO-01 presents the EQE_max of 20.2%. These results pave a novel avenue for designing highly efficient deep blue emitter in solution processable OLED.