Fused π‐Extended Multiple‐Resonance Induced Thermally Activated Delayed Fluorescence Materials for High‐Efficiency and Narrowband OLEDs with Low Efficiency Roll‐Off

• Published in: Advanced optical materials Vol. 10; no. 9
• Main Authors: Luo, Xu‐Feng, Ni, Hua‐Xiu, Ma, Hui‐Li, Qu, Zhong‐Ze, Wang, Jie, Zheng, You‐Xuan, Zuo, Jing‐Lin
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-05-2022
• Subjects: Carbazoles; Charge transfer; Doped films; Efficiency; Electroluminescence; Emitters; Energy gap; Fluorescence; low efficiency roll‐off; Materials science; multiple‐resonance induced thermally activated delayed fluorescence; Narrowband; narrowband emission; Nitrogen; Optics; Organic light emitting diodes; Photoluminescence; Quantum efficiency; Rate constants; Resonance; reverse intersystem crossing
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202102513

The simultaneous achievement of multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) materials with strong narrowband emission and efficient reverse intersystem crossing (RISC) process can further promote the advancement of organic light‐emitting diodes (OLEDs). Herein, a new strategy is proposed to achieve two π‐extended MR‐TADF emitters (NBO and NBNP) peaking at 487 and 500 nm via fusing conjugated high‐triplet‐energy units (carbazole, dibenzofuran) into boron‐nitrogen (B/N) framework, aiming to increase charge transfer delocalization of the B/N skeleton and minimize singlet‐triplet energy gap (∆EST). This strategy endows the two emitters with full width at half maximum of 27 and 29 nm, and high photoluminescence efficiencies above 90% in doped films, respectively. Additionally, considerable rate constants of RISC are obtained due to the small ∆EST (0.12 and 0.09 eV) and large spin‐orbital coupling values. Consequently, the OLEDs based on NBO and NBNP show the maximum external electroluminescence quantum efficiency of up to 26.1% and 28.0%, respectively, accompanied by low‐efficiency roll‐off. These results provide a feasible design strategy to construct efficient MR‐TADF materials for OLEDs with suppressed efficiency roll‐off.
Two high‐efficiency boron‐nitrogen (B/N) framework‐based multiple‐resonance thermally activated delayed fluorescence emitters with π‐extended and fused conjugated high‐triplet‐energy units show small singlet‐triplet energy gap and large spin‐orbital coupling values with full widths at half maximum of 27 and 29 nm, respectively. The corresponding organic light‐emitting diodes display high external quantum efficiencies of up to 26.1% and 28.0% with low‐efficiency roll‐off.