Synthesis Of Benzimidazole Iridium Complex And Their Electroluminescent Properties Under Different Processes

Organic electroluminescent diodes（OLEDs）have developed tremendously since they were born over 30 years ago.Because of their advantages such as high brightness,wide viewing angle,and easy large-area manufacturing,OLEDs have received extensive attention in the new generation of solid-state lighting and flat-panel displays.Organic electroluminescent material is one of the important components of organic light-emitting devices.Among them,the phosphorescent material can theoretically reach the maximum internal quantum efficiency of 100%due to the simultaneous utilization of singlet and triplet excitons.Therefore,phosphorescent materials have obvious advantages in the application of OLEDs.The study of transition metal iridium complexes as luminescent materials has gradually become one of the research focuses of organic electroluminescence.In light of the advantages of stable molecular structure,excellent electron transport performance,and high luminous efficiency,benzimidazole iridium complexes have attracted extensive attention from scientific researchers.In this work,a series of new benzimidazole-iridium complexes were designed and synthesized through the modification of benzimidazole,and their photophysical properties and electroluminescence properties were studied.Focusing on the iridium complex with（2,6-difluoropyridine）group which promotes dissolution,we studied the effect on the electroluminescence performance of the devices prepared under different processes.The specific work is as follows:（1）The trifluoromethyl group was introduced into the benzimidazole ring part for the first time,and four new benzimidazole derivatives iridium complexes（tpb）₂Ir（acac）、（ttpb）₂Ir（acac）、（mtpb）₂Ir（acac）、（btpb）₂Ir（acac）were synthesized,The maximum emission wavelengths of the four iridium complexes are 517,528,499 and529 nm,respectively,and the luminous efficiencies are 78.6,92.2,87.6 and 74.6%,respectively.All complexes have good thermal stability.The vacuum evaporation devices of these complexes all show excellent electroluminescence performance,Among them,the doped device based on（ttpb）₂Ir（acac）shows the highest efficiency,the maximum external quantum efficiency,maximum current efficiency,and maximum power efficiency are 17.8%,61.8 cd A^-1,28.7 lm W^-1 with low efficiency roll-off.（2）A benzene ring was introduced at the 6 and 7 positions of the benzimidazole,and two naphthimidazole derivatives iridium complexes（dndi）₂Ir（acac）and（dpndi）₂Ir（acac）were designed and synthesized.The maximum emission wavelengths of the two complexes are 511 and 517 nm.Compared with the parent benzimidazole iridium complex,they have a blue shift of 10-20 nm.Among them,the device based on（dndi）₂Ir（acac）has better excellent performance with the maximum efficiencies,the maximum external quantum efficiency,maximum current efficiency,and maximum power efficiency are 15.2%,51 cd A^-1,and 28.7 lm W^-1.（3）Through introducing 2,6-difluoropyridine into the benzimidazole,the target iridium complex（dtpb）₂Ir（acac）was designed and synthesized.The maximum emission wavelength of（dtpb）₂Ir（acac）is 479 nm.The luminous efficiency of（dtpb）₂Ir（acac）is as high as 95.6%,and its thermal decomposition temperature（5%decomposition）is 335℃.The（dtpb）₂Ir（acac）-doped devices was initially prepared with different processes including vacuum evaporation,inkjet printing,and spin coating,and all exhibited excellent electroluminescence properties.The doped device prepared based on the vacuum evaporation method achieved excellent performance of18.1%,51.5 cd A^-1,and 27 lm W^-1.Based on the doped devices prepared by the inkjet printing method and the spin coating method with the annealing temperature 80℃of the light-emitting layer,the devices achieved the best performance,the maximum external quantum efficiency,maximum current efficiency,and maximum power efficiency are 7.9%,22.6 cd A^-1,14.2 lm W^-1 and 2.9%,8.2 cd A^-1,5.7 lm W^-1,respectively.