A New Molecular Design Based on Thermally Activated Delayed Fluorescence for Highly Efficient Organic Light Emitting Diodes

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• 作者：Pachaiyappan Rajamalli ; Natarajan Senthilkumar ; Parthasarathy Gandeepan ; Pei-Yun Huang ; Min-Jie Huang ; Chen-Zheng Ren-Wu ; Chi-Yu Yang ; Ming-Jui Chiu ; Li-Kang Chu ; Hao-Wu Lin ; Chien-Hong Cheng
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：January 20, 2016
• 年：2016
• 卷：138
• 期：2
• 页码：628-634
• 全文大小：447K
• ISSN：1520-5126

文摘

Two benzoylpyridine-carbazole based fluorescence materials DCBPy and DTCBPy, bearing two carbazolyl and 4-(t-butyl)carbazolyl groups, respectively, at the meta and ortho carbons of the benzoyl ring, were synthesized. These molecules show very small ΔE_ST of 0.03 and 0.04 eV and transient PL characteristics indicating that they are thermally activated delayed fluorescence (TADF) materials. In addition, they show extremely different photoluminescent quantum yields in solution and in the solid state: in cyclohexane the value are 14 and 36%, but in the thin films, the value increase to 88.0 and 91.4%, respectively. The OLEDs using DCBPy and DTCBPy as dopants emit blue and green light with EQEs of 24.0 and 27.2%, respectively, and with low efficiency roll-off at practical brightness level. The crystal structure of DTCBPy reveals a substantial interaction between the ortho donor (carbazolyl) and acceptor (4-pyridylcarbonyl) unit. This interaction between donor and acceptor substituents likely play a key role to achieve very small ΔE_ST with high photoluminescence quantum yield.