Xing Chen ,Guoyun Meng, Guanming Liao, Florian Rauch, Jiang He, Alexandra Friedrich, Todd Marder, Nan Wang, Pangkuan Chen, Suning Wang, Xiaodong Yin*, Highly Emissive 9‐Borafluorene Derivatives: Synthesis, Photophysical Properties, and Device Fabrication, Chem. Eur. J. 10.1002/chem.202005185

A series of 9‐borafluorene derivatives, functionalised with electron‐donating groups, was prepared. Some of these 9‐borafluorene compounds exhibit strong yellowish emission in solution and in the solid state with relative high quantum yields (up to 73.6% for FMesB‐Cz as a neat film). Highly twisted donor groups suppress the charge transfer but the intrinsic photophysical properties of 9‐borafluorene systems remain and the new compounds possess enhanced stability to the atmosphere. All of these compounds exhibit excellent thermal stability, revealing their potential for applications in materials science. OLED devices were fabricated with two of the highly emissive compounds, and they exhibit strong yellow‐greenish electro‐luminescence with maximum luminance intensity > 22000 cd·m ‐2 . This is the first example of 9‐borafluorene derivatives being used as light‐emitting materials in OLED devices, and helps us to achieve a balance between maintaining their intrinsic properties and improving their stability.