Isomeric spiro-[acridine-9,9′-fluorene]-2,6-dipyridylpyrimidine based TADF emitters: insights into photophysical behaviors and OLED performances

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 6; no. 37; pp. 10088 - 10100
• Main Authors: Ganesan, Paramaguru, Chen, Deng-Gao, Liao, Jia-Ling, Li, Wei-Cheng, Lai, Yi-Ning, Luo, Dian, Chang, Chih-Hao, Ko, Chang-Lun, Hung, Wen-Yi, Liu, Shun-Wei, Lee, Gene-Hsiang, Chou, Pi-Tai, Chi, Yun
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2018
• Subjects: Crystallography; Diodes; Dipoles; Electroluminescence; Emitters; NMR; Nuclear magnetic resonance; Organic light emitting diodes; Quantum efficiency; Structural design
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/C8TC03645D

TADF molecules with a higher horizontal–dipole ratio have recently been realized to show a large conversion efficiency in organic light-emitting diodes (OLEDs) and hence great promise for their application in display and solid state lighting sources. The current work focuses on fine-tuning the structure of the parent 2,6-diphenylpyrimidinyl compound PhPMAF and its derivatives with a series of 2,6-dipyridylpyrimidine acceptors; namely: 2NPMAF , 3NPMAF and 4NPMAF , among which the intramolecular CH⋯N bonding interaction was confirmed for 2NPMAF , showing good agreement with the NMR results. The solvatochromism and TADF behaviors, together with TD-DFT computations, of the titled compounds were explored to gain insights into the structure–photophysics relationship. Eventually, these functional 2,6-dipyridylpyrimidine acceptor based TADF compounds exhibit electroluminescence ranging from deep-blue to sky-blue, among which an external quantum efficiency (EQE) of 24.9% was achieved for the derivative 3NPMAF . The high horizontal–dipole ratios (∼0.86–0.91) obtained for this class of compounds elucidates the superior OLED performance. Moreover, the non-doped OLED architecture achieves an EQE of 14.1% for 3NPMAF , which is superior to that of PhPMAF with an EQE of 5.1%, demonstrating the significance of dipyridylpyrimidine as an acceptor for the future structural design of TADF emitters.