Design And Synthesis Of Nitrogen-containing Heterocyclic Aromatic Phosphine Oxide Photoelectric Functional Materials

The carbazoles and phosphine oxide-based hosts have their own unique advantages,which has always been attracting attentions and being studied,it is considered as one of the most important approaches for overcoming the drawbacks of blue phosphorescent OLEDs,such as high driving voltages,low device efficiency and quickly roll-off.In this paper,on the basis of substitution of carbazole at its N,3 and 6 positons with tert-butyl,methyl and phenyl,respectively,diphenylphosphine oxide groups were introduced in its 1,8-position to form short-axis substitution configuration.Through constructing D-A-type bipolar structure,the optoelectornic properties of the resulted hosts were selectively moduclated.By varying the number of phosphine oxide groups and the intramolecular interactions,the electron injection and transportation was enhanced on the basis of unchanged triplet energy and preserved hole injection and transportation to the biggest extent.The investigation showed that all of the carbazole-phosphine oxide hybrids possess the high triplet energy of~2.9 eV.The introduction of phosphine oxide groups induced the reduction of LUMO for 0.2 eV,which is bigger than that of HOMO.1.Based on tBCzMSPO as host for red,green,yellow and blue PHOLEDs had achieved a high efficient and ultra low voltage.The driving voltages for blue PHOLEDs was 2.6 V,and showed the maximum efficiencies of 20.2 cd/A for current efficiency,19.2 lm/W for power efficiency,11.0%for external quantum efficiency.At100 cd/m~2,the efficiency roll-off was 13,18 and 13%.The Green,yellow and red devices turn-on voltages were 2.6 V,3 V and 3 V,the maximum current efficiency were 33.1,17.6 and 3 cd/A.2.The Green and blue PHOLEDs based on tBCzPXPO as host achieved a better device performance.Its drive voltage was 2.6V,and the practical brightness from100-1000 cd/m~2 for display and lighting has a very low turn-on voltage,3 and 4 V,respectively.The blue devices of tBCzPSPO as host of the maximum current efficiency,maximum power efficiency and the external quantum efficiency were 15.4cd/A,18.3 lm/W and 8.1%.The green device of tBCzPSPO as host has 23.5 cd/A for current efficiency,25.2 lm/W for power efficiency and 6.8%for external quantum efficiency.This thesis verified that at the same time of preserving triplet energy levels by short-axis linkage strategy,frontier molecular orbital energy levels can be selectively tuned for a series of low-voltage-driven electrophosphorescent host materials with favorable device performance.