RESUMO
Chiral conjugated polymer has promoted the development of the efficient circularly polarized electroluminescence (CPEL) device, nevertheless, it remains a challenge to develop chiral polymers with high electroluminescence performance. Herein, by the acceptor copolymerization of axially chiral biphenyl emitting skeleton and benzophenone, a pair of axially chiral conjugated polymers namely R-PAC and S-PAC are synthesized. The target polymers exhibit obvious thermally activated delayed fluorescence (TADF) activities with high photoluminescence quantum yields of 81%. Moreover, the chiral polymers display significant circularly polarized luminescence features, with luminescence dissymmetry factor (|glum|) of nearly 3 × 10-3. By using the chiral polymers as emitters, the corresponding circularly polarized organic light-emitting diodes (CP-OLEDs) exhibit efficient CPEL signals with electroluminescence dissymmetry factor |gEL| of 3.4 × 10-3 and high maximum external quantum efficiency (EQEmax) of 17.8%. Notably, considering both EQEmax and |gEL| comprehensively, the device performance of R-PAC and S-PAC is the best among all the reported CP-OLEDs with chiral conjugated polymers as emitters. This work provides a facile approach to constructing chiral conjugated TADF polymers and discloses the potential of axially chiral conjugated luminescent skeletons in architecting high-performance CP-OLEDs.
RESUMO
The intrinsic helical π-conjugated skeleton makes helicenes highly promising for circularly polarized electroluminescence (CPEL). Generally, carbon helicenes undergo low external quantum efficiency (EQE), while the incorporation of a multi-resonance thermally activated delayed fluorescence (MR-TADF) BN structure has led to an improvement. However, the reported B,N-embedded helicenes all show low electroluminescence dissymmetry factors (gEL), typically around 1×10-3. Therefore, the development of B,N-embedded helicenes with both a high EQE and gEL value is crucial for achieving highly efficient CPEL. Herein, a facile approach to synthesize B,N-embedded hetero[9]helicenes, BN[9]H, is presented. BN[9]H shows a bright photoluminescence with a maximum at 578â nm with a high luminescence dissymmetry factor (|glum|) up to 5.8×10-3, attributed to its inherited MR-TADF property and intrinsic helical skeleton. Furthermore, circularly polarized OLED devices incorporating BN[9]H as an emitter show a maximum EQE of 35.5 %, a small full width at half-maximum of 48â nm, and, more importantly, a high |gEL| value of 6.2×10-3. The Q-factor (|EQE×gEL|) of CP-OLEDs is determined to be 2.2×10-3, which is the highest among helicene analogues. This work provides a new approach for the synthesis of higher helicenes and paves a new way for the construction of highly efficient CPEL materials.
RESUMO
A new fluorescent emitter based on π-extended benzothiadiazole was synthesized. The emitter exhibited a large molar extinction coefficient, a high quantum yield of 98% and a large radiative decay rate of 108 s-1. Moreover, the obtained TADF-sensitized fluorescent OLED displayed excellent device performance with a high EQEmax of 14.3%.