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

Abstract

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 (S1) and triplet excited state (T1) (that is, ΔEST) 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.