Synthesis And Photoelectric Properties Of Blue-light Emitting Thermally-activated Delayed Fluorescence Materials Based On Carbazole Derivatives

Over the past decades, OLED has attracted much attention due to its superior advantages compare to the traditional flat panel display and lighting. In the preparation and optimization of OLED, the selection of luminescent material is crucial, whose properties are one of the important factors to the device performance. Compared with the green and red light emitting materials, blue light materials are relatively backward. There are few stable deep blue light emitting materials, the efficiency and lifetime have yet to be improved. In recent years, Completely organic thermally activated delayed fluorescence materials, one of the third generation electroluminescent materials by design and synthesis without transition metal, have make a figure because of its various advantages, such as high internal quantum efficiency which is nearly 100% theoretically, good stability and low-cost etc. Develop the new type TADF blue light materials has become one of the hot research topics.And the compound carbazole, for one thing, which has high triplet energy level and excellent hole transmission characteristics with deep blue light of its own, for another, the compounds can increase the steric hindrance, improve the hole injection and transport capacity by introducing the carbazole. So this work is about take advantage of the characteristics of carbazole to modify the chemical structure and regulate the energy level and emitting light colors by change the structure of accept units or conjugation of donor units, as far as the relationship between TADF material structures and properties. Based on mentioned above, we have done the following work:1. Regulate the emitting light colors and adjust the ΔE ST by introducing F atoms as the second charge accept unit: synthesis the carbazole derivative based on 4-fluorobenzonitrile as the core unit: 2,3,5,6-tetracarbazole-4-fluorobenzomitrile(Cy Fb Cz). The compound shows excellent thermal stability and high stability of amorphous with high glass transition temperature of 170 ℃ and decomposition temperature of 429 ℃ as a type of new TADF blue light emitting mater ial(λPL was located at 428 nm in toluene) with small ΔE ST(0.09 e V) and short delay fluorescence lifetime(12.8 μs). The EL spectrum for the preparation of doped Cy Fb Cz OLED device is located at 448 nm and shows blue light emission. And the OLED based on Cy Fb Cz exhibited blue emission with a maximum luminance of 2526.8 cd/m2, a maximum current efficiency of 6.64 cd/A, a maximum power efficiency of 2.66 lm/W, and a low turn-on voltage of 4.1V. 2. By introducing carbazole dendrons, change the conjugation of electron donor, adjust the ΔE ST, try to prepare the non-doped device: synthesis the TADF materials of carbazole dendrimers based on diphenylsulfone as the core unit: Bis(4-(3,6-di-tert-butylcarbazole-N-yl)phenyl)(G1), Bis(4-(3,6-Bis(3,6-di-tert-butylcarbazol-N-yl)carbazole)phenyl) sulfone(G2), Bis(4-(3,6-Bis-(3,6-Bis(3,6-di-tert-butylcarbazol-N-yl)carbazole) carbazole) phenyl) sulfone(G3). The compounds G1,G2 and G3 as a new breed of TADF blue light matirals(λPL were located at 406 nm, 437 nm and 439 nm in toluene, respectively) show excellent thermal stability with high glass transition temperature of 179 ℃, 243 ℃ and 323 ℃, respectively, with small ΔE ST(0.08 e V, 0.07 e V and 0.04 e V, respectively). Among them, the non-doped single layer OLED device based on G2 as luminescent material exhibits strong blue light emission, EL peak is located at 434 nm, 4 nm blue shift compared with PL peak in the toluene solution. And the device achieves a maximum luminance of 2313 cd/m2, a maximum current efficiency of 4.07 cd/A, a maximum power efficiency of 3.28 lm/W and a low turn-on voltage of 2.9 V.