Design,Synthesis And Photoelectric Properties Of Blue Organic Luminescent Materials Based On Triazole Groups

After just a few decades of development,organic electroluminescent diodes(OLEDs)have been widely used in information display and solid-state lighting.As we all know,blue light,as one of the three primary colors required for organic lightemitting semiconductor materials,is indispensable in panchromatic display.Blue light materials with excellent performance can reduce the power consumption of the panel,Moreover,they can be used as host materials because of their wideband gap properties.At present,based on the blue phosphorescent materials of Ir and Pt metal complexes and TADF materials,although the utilization rate of excitons can reach 100% and the device efficiency is high,the device stability is poor and the service life of the device is not up to commercial standards.Therefore,the most used blue light OLED materials are still the traditional fluorescent materials.In order to obtain electroluminescent devices with excellent performance,many devices need to be prepared by doping host and guest with each other,and host materials with matching energy levels are required.The doping concentration of guest materials is optimized and controlled by evaporation technology,thus increasing the cost of device fabrication,at the same time,the light stability of the device will be affected.Therefore,from the development and selection of materials,it is of great significance to design and synthesize organic blue light materials with good stability and excellent performance that can be used in non-doped devices.In recent years,molecular structure design based on donor-acceptor(D-A)linkage has attracted extensive attention.Since D-A type materials have good carrier transport performance,the luminescent performance of the materials can be adjusted by selecting the acceptor groups and using different connection sites.However,D-A type molecules are prone to intramolecular charge transfer(ICT)effect,which is not conducive to obtaining ideal blue light materials.In order to obtain blue light materials with excellent performance,it is very important to select the appropriate donor and acceptor group.In the blue color gamut,although high-energy blue light is indispensable in the field of display and lighting,it is also very harmful to human body.Recently,related studies have reported that low-energy blue-green light(465-495 nm)does little harm to human body and is conducive to the regulation of human circadian rhythm.Therefore,it is of great significance for solid lighting and display to obtain blue light materials suitable for the range.In order to adjust the electroluminescence color of the material,We took triazole derivatives as the acceptors and phenanthroimidazole derivatives as the donors to construct two highly efficient donor-acceptor(D-A)type blue emitters,TAZ-PPI and4NTAZ-PPI.Besides,the EL performance can be greatly improved by changing the structure design of N4 position of triazole derivatives linked with phenyl or naphthalene.The photoluminescence fluorescence quantum yield(PLQY)of the two films was more than 60%.In addition,the maximum external quantum efficiency(EQE)of non-doped electroluminescent devices based on 4NTAZ-PPI and TAZ-PPI are 7.3% and 5.9%,respectively.The efficiency roll-down of the non-doped devices of the both materials is very small at high brightness,which significantly improves the stability of the devices.At the same time,the main peaks of the electroluminescence spectra of the two materials are located at 460 nm and the pure blue light emission is realized.Therefore,the two materials have a broader application prospect.In order to further improve the electroluminescence properties of the materials,we choose the electron-withdrawing groups triazole as the acceptor material,triphenylamine(TPA)as the donor,anthracene(An)as a bridge between donors and acceptor groups,and synthesized D-?-A type of organic fluorescent material,TAZ-AnTPA.The non-doped device of TAZ-An-TPA exhibits blue light emission,and the main peak of the electroluminescence spectrum is at 476 nm.The maximum EQE is 6.7%.Then we further optimized the doped device of TAZ-An-TPA.The emission peak of the doped device with CBP as the host material is 464 nm,the spectrum is blue shifted by12 nm relative to the non-doped device.Its electroluminescence was also in the blue emission range.Meanwhile,the maximum EQE was 8.9%,which effectively improved the device performance of the organic light-emitting material with triazole as the acceptor.