Synthesis And Characterization Of High Fluorescence Quantum Yields Blue Small Molecule Material For Organic Light-Emitting Diodes

Organic Light-Emitting Diodes (OLEDs) since it has wide view angle, low driving voltage, high luminous efficiency, fast response speed, flexible display, easy operation and excellent performance has been widely used for applications of full-color flat-panel displays and thin in the large area of flat panel display. Compared to the red and green light material performance and device stability, efficiency, life and color purity of blue electroluminescent materials need to further improve. There are many challenges such as emission efficiency, transmission performance, charge balance injection, morphology and thermodynamic optimization for multi-function blue fluorescent material synthesis. Solution-processible OLEDs have recently received great attention due to the cost-efficient fabrication from solution and significant potential applications in flat-displays and flexible display. For achieving high device performance, molecular design can introduce hole-transporting or/and electron-transporting groups in luminescent material, and optimize the device structure add the hole and electron transport layer to realize the light-emitting layer carrier balance by adding hole transport layer and electron transport. In order to increase efficiency of devices, triplet excitons are transformed to singlet excitons via RISC in TADF materials. As a result, both triplet and singlet excitons can be harvested. Hence, development of high efficiency and high brightness of blue fluorescent OLED has the very vital significance.In this thesis, we have designed and synthesized a series of novel solution-processing fluorescent light-emitting materials and thermally activated delayed fluorescence materials. The thermal property, electrochemical and photophysical properties of the materials and device performance have been systematically investigated, and the high photoluminescence quantum efficiencies solution-processed fluorescent OLEDs have also been fabricated. The main contents are decribed as follows:(1) A series of 9,10-diphenyl-anthracene derivatives bearing either benzimidazole or carbazole moieties as substituents materials were synthesized and characterized as blue emitters for organic light-emitting diodes (OLEDs). The good solubility of tert-butyl in CAC can show excellent film forming ability in solution-processed device fabrication, and achieve the efficient and stable OLED possible. The the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of CAC are 5.23 eV and 2.25 eV, respectively, which match the HOMO energy level (5.2 eV) of the hole injection layer of PEDOT:PSS. The film maximum emission wavelength and fluorescence quantum efficiency of CAC are 439 nm and 0.87, respectively. The solution processed doped deep-blue emitting device of CAC exhibited a maximum luminance efficiency of 3.03 cd/A, a maximum power efficiency of 1.64 lm/W and a maximum external quantum efficiency of 2.81% with CIE (0.16,0.10).(2) A series of blue thermally activated delayed fluorescence materilas based on cyano and carbazole have been synthesized and characterized. The ?Est in these materilas are around 0.1 eV by systematically changing the electron acceptor units. Higher thermal decomposition temperature and glass transition temperature show good thermal stability. The D-A structure of these molecules can effectively reduce the energy gap between triplet energy level and singlet energy levels and have obvious solvent effect in different solvents. This series of molecules has become the potential of TADF materials with good performance through the theoretical calculation and experiment. The donor and acceptor units are largely twisted relative to each other with non-planar structure. For efficient RISC, a small energy gap (?Est) between the lowest excient Si and T1 states is needed. Small ?Est can be attained by minimizing the exchange energy between the Si and Ti states, which can be achieved by reducing the special overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). This will lay the foundation for achieving excellent efficiency thermally activated delayed fluorescence devices.