Rational Molecular Design of Multifunctional Blue‐Emitting Materials Based on Phenanthroimidazole Derivatives

• Published in: Chemistry : a European journal 2021-05, Vol.27 (25), p.7275-7282
• Main Authors: Chen, Xiang, Zhang, Hao, Tan, Hong‐Ji, Yang, Liu, Qin, Peng, Zheng, Xu‐Hui, Tang, Shan‐Shun, Liu, Yu, Tong, Qing‐Xiao
• Format: Article
• Language: English
• Subjects: Charge transfer; Chemistry; Design; Emitters; Emitters (electron); Empirical analysis; fluorescence; HLCT emitters; intersystem crossing; light-emitting diodes; Mathematical analysis; nitrogen heterocycles; Optimization; Organic light emitting diodes; Phosphorescence; Planar structures; Pyridines
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202005214

High‐performance deep‐blue emitters with external quantum efficiencies (EQEs) exceeding 5 % are still scarce in organic light‐emitting diodes (OLEDs). In this work, by introducing a [1,2,4]triazolo[1,5‐a] pyridine (TP) unit at the N1 position of phenanthroimidazole (PI), two luminescent materials, PTPTPA and PTPTPA, were obtained. Systematic photophysical analysis showed that the TP block is suitable for constructing hybridized local and charge‐transfer (HLCT) emitters. Its moderate electron‐withdrawing ability and rigid planar structure can enhance the CT component while ensuring color purity. In addition, compared with PTPTPA, the additional phenyl ring of PTPBPTA not only increased the oscillator strength, but also decreased the Stokes shift. TDDFT calculations pointed out facile reverse intersystem crossing processes in PTPTPA from high‐lying triplet states to the singlet excited state. A nondoped device based on PTPTPA as emitter showed impressive performance with EQEmax of 7.11 % and CIE coordinates of (0.15, 0.09). At the same time, it was also an efficient host for yellow and red phosphorescent OLEDs. By doping yellow (PPYBA) and red (BTPG) phosphorescent dyes into PTPTPA, a white OLED with a high EQE of 23.85 % was achieved. The successful design of PTPTPA not only provided an optimization choice for OLED emitters, but also demonstrated the empirical rules for the design of multifunctional deep‐blue emitters. Deeper blue: On the basis of multifunctional phenanthroimidazole‐based material PTPBPTA, which acts both as a deep‐blue fluorescent emitter and as a host material for phosphors, high‐performance deep‐blue fluorescent organic light‐emitting diodes (OLEDs), yellow and red phosphorescent OLEDs, and a white OLED were fabricated.