Synthesis, Properties and Applications of Biphenyl Functionalized 9,9-Bis(4-diphenylaminophenyl)fluorenes as Bifunctional Materials for Organic Electroluminescent Devices

Four new bifunctional materials, namely BPTF, CBPTF, CMBPTF and BPVTF, having 9,9-bis(4-diphenylaminophenyl)fluorene as a molecular platform and biphenyl derivatives as end-capping substituents were synthesized and characterized. Their optimized structures revealed that both triphenylamine moieties at the C-9 position of the fluorene ring generated a bulky molecular structure. These molecules showed strong blue emission in both solution and in the solid state, and were thermally stable amorphous materials with glass transition temperatures up to 207 degrees C. The abilities of these materials to act as blue-light-emitting materials for blue OLEDs and hole-transporting materials for green OLEDs in terms of device performance and thermal properties were superior to commonly used N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB). Efficient, and bright nondoped deep-blue and Alq3-based green OLEDs with maximum luminance efficiencies and CIE coordinates of 2.48 cd?A1 and x = 0.15 and y = 0.07, and 4.40 cd?A1 and x = 0.28 and y = 0.52 were achieved, respectively, with BPTF having two biphenyl substituents as active layers. Both devices showed low turn-on voltages of 3.1 and 2.8 V, respectively. Notably, the color purities of these deep-blue and green devices were close to the National Television Standards Committee blue (CIE coordinates of x = 0.14 and y = 0.08) and green (CIE coordinates of x = 0.26 and y = 0.65) standards.