Study On The Construction Of Simple Organic Blue Molecules Based On Pheumidazole Groups And Their Photoelectric Properties

Blue organic fluorescent materials play a vital role in the field of full-color display and solid-state lighting of organic light-emitting diodes(OLEDs).At present,blue light organic materials mainly face the following problems:1.The design and synthesis process of most blue light molecules with excellent performance is complicated and cumbersome,and it is difficult to obtain blue organic electroluminescent materials with excellent properties through a simple synthesis process,and the complicated synthesis process will undoubtedly increase its cost and limit the next step of Commercial application.2.In designing HLCT-type blue light molecules,it is difficult to grasp the balance between the charge transfer state(CT state)component and the local state(LE state)component.An excessively strong CT state will cause the light color of the molecule to redshift,affect the color purity of the molecule,and reduce the luminous efficiency of the molecule,while the pure LE state will limit the exciton utilization rate of the molecule.3.The wider band gap leads to the difficulty of carrier injection in molecular material devices.In response to the above-mentioned problems,this paper adopts a new and simple synthesis method to design and synthesize a series of molecules,and systematically study the relationship between their structure and performance.First,pyridine and cyano are used to modify the phenanthrimidazole to obtain two molecules of PIPYCN and PYPIPY.The maximum external quantum efficiency of non-doped OLEDs with PIPYCN and PYPIYP as the light-emitting layer is 2.2%and 3.5%,respectively,the brightness is 3801 cd m-2and 2001 cd m^-2,and the corresponding exciton utilization rate is 41.35%and 41.17%,the exciton utilization rate has exceeded the 25%spin statistical limit.The high exciton utilization rate comes from the hybrid local charge transfer(HLCT)state in the molecule.In order to further improve the electroluminescence properties of the device.We designed and synthesized two molecules,CH₃OPICN and CH₃OPICONH₂,and analyzed the effects of different modification groups on the molecular structure and performance by studying their photophysical properties and electroluminescence properties.Both the excited states of the two compounds show the characteristics of the HLCT excited state.And they all show a twisted molecular structure,showing deep blue luminescence in the solid state.The device with CH₃OPICN as the light-emitting layer has a maximum external quantum efficiency of 3.5%and a brightness of 13613 cd m^-2,and the device with CH3OPICONH2 as the light-emitting layer has a maximum external quantum efficiency of3.2%and a brightness of 6364 cd m^-2.When the brightness is 1000 cd m^-2,the efficiency roll-off is 8.57%and 15.62%respectively.Compared with PIPYCN and PYPIYP,the brightness has been significantly improved,and the external quantum efficiency has been significantly improved.By comparing the electroluminescence properties of the four molecules,we found that inserting the donor group at the N1 position of the phenanthroimidazole and the acceptor group at the C2 position is an effective method to obtain a luminescent material with ideal performance..