Structural Engineering of Deep-Blue Emitters (Imidazoles Integrated with Triphenylamine) Leads to EQE > 6% and High Color Purity (CIEy ∼ 0.09) for Solution-Processed OLEDs

• Published in: Journal of physical chemistry. C Vol. 127; no. 33; pp. 16623 - 16635
• Main Authors: Girase, Jaipal Devesing, Singh, Sunidhi, Debata, Bhabana Priyadarshini, Nayak, Sandhya Rani, Nagar, Mangey Ram, Jou, Jwo-Huei, Patel, Sabita, Vaidyanathan, Sivakumar
• Format: Journal Article
• Language: English
• Published: American Chemical Society 24.08.2023
• Subjects: C: Physical Properties of Materials and Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.3c03058

Solution-processable efficient deep-blue emitters, mainly those approaching National Television System Committee (NTSC) coordinates of Commission International de l’Eclairage (CIE) (0.14, 0.08), are highly essential for full-color displays. However, efficient deep-blue fluorescent emitters with good efficiency and color purity are still rare. Therefore, in the current study, three new donor–π–acceptor (D–π–A) thermally stable blue emitters, 4′-(4,5-diphenyl-1-(p-tolyl)-1H-imidazol-2-yl)-N,N-diphenyl-[1,1′-biphenyl]-4-amine (4-BIPTPA), 3′-(4,5-diphenyl-1-(p-tolyl)-1H-imidazol-2-yl)-N,N-diphenyl-[1,1′-biphenyl]-4-amine (3-BIPTPA), and N,N-diphenyl-3′-(1-(p-tolyl)-1H-phenanthro­[9,10-d]­imidazol-2-yl)-[1,1′-biphenyl]-4-amine (3-PIPTPA), by integrating a triphenylamine (TPA) moiety with diphenylimidazole (BI)/phenanthroimidazole (PI) with different linking arrangements between the donor and acceptor and functionalization at the N1 position of imidazole with the electron-donating (p-tolyl) moiety have been successfully designed and synthesized. These emitters exhibit blue emission in solution and solid. In addition, these emitters are capable of transporting both holes and electrons and forming bipolar compounds. Hence, here, undoped and doped organic light-emitting devices with newly synthesized emitters were fabricated. Among all of the doped devices, the device based on the 4-BIPTPA emitter as a dopant showed deep-blue emissions with excellent device performance with an EQEmax of 6.2% and CIE coordinates of (0.17, 0.14) at 5 wt % doping concentration, and the doped device based on 3-PIPTPA showed deep-blue emissions with an EQEmax of 6.0%, a power efficiency (PEmax) of 2.8 lm W–1, a current efficiency (CEmax) of 3.1 cd A–1, and CIE coordinates of (0.17, 0.09) at 1 wt % doping concentration, nearly equal to the NTSC blue standard.