Blue thermally activated delayed fluorescence emitters based on a constructing strategy with diversed donors and oxadiazole acceptor and their efficient electroluminescent devices

摘要

A series of highly efficient blue emission compounds with D-A-D molecular structures were designed and synthesized, in which oxadiazole group was used as electronic acceptor (A), and carbazole/acridine groups as electronic donor (D). It is found that the compounds containing acridine both had small energy splitting between singlet excited state (S-1) and triplet excited state (T-1) (that is, Delta E-ST) and thus showed distinct thermally activated delayed fluorescence (TADF) characteristics. Moreover, they both had high photoluminescent quantum yields (PLQY) even up to 93%. In comparison, the compound only containing carbazole just showed prompt emission but no delayed fluorescence. The blue organic light-emitting diodes (OLEDs) using the TADF compounds as emitters achieved a high maximum external quantum efficiencies (EQE) up to 22.3% with Commission Internationale de L'e'clairage (CIE) coordinates of (0.16, 0.24). Triplet excitons were efficiently utilized in the device. The further optimized OLEDs achieved more outstanding comprehensive performance.