The Synthesis Of Bipolar Host Materials And Their Application In Phosphorescent OLEDs With Solution Processing

Phosphorescent organic light-emitting diodes(PhOLEDs)can achieve 100%internal quantum efficiency theoretically by using the single and triple excited states at the same time.However,the effect of spin-orbit couping can easy lead to triplet-triplet annihilation and concentration quenching.Thus,in order to resolve the impacts,the phosphor materials are normally doped into the host materials as the guest materials.Therefore,it is important to develop the host materials.In this thesis,we have synthesized two bipolar host materians with triphenylamine/carbazole as electron-donating moiety and imidazole as electron-withdrawing moiety.All the as-synthesized compounds have good solubility in common solvents(tetrahydrofuran,chlorobenzene,etc.).Thermal,photophysical properties,negligible solvent effect and combined with electrochemistry calculations and theory calculations,the feasibility of fabricating the red,green and blue PhOLEDs by solution processing were discussed.The target compounds possessed good thermal stabability with high decomposition temperature(T_d>290°C)and glasstransition temperature(T_g>125°C).The photo-fluorescent spectra of target moleculars both in solution and film state showed deep blue emission maintained fabricate red and green devices.Negligible solvent effect demonstrated the existence of HLCT state and the feasibility of achieving blue PhOLEDs.The researches of space charge-limited current and electrochemistry calculations were used to design the configurations of devices.All the devices were fabricated by low-cost solution processing,the as-synthesized compounds were applied as emitting layer in fluorescence OLEDs.The results showed that compound 1 had not any emitting phenomenon because of the low fluorescent quantum yield,and compound 5 showed deep blue emission.As host materials applied in the fabrication of red,green and blue phosphorescent OLEDs,the roll-off problems were well solved.The current efficiencies of devices were 0.12,2.20,0.014 cd/A and 0.98,13.42,0.083 cd/A for compounds 1 and 5,respectively.