Design,Synthesis And Properties Of Efficient Red Phosphorescent Ir(?) Complexes And Host Materials

In the field of lighting and display industries,organic light emitting diodes(OLEDs)have attracted much attention by the virtue of thin,light texture,high brightness,fast response and wide viewing angle properties.OLEDs can achieve full-color self-emission from red to blue light.But current research on blue and red OLEDs lags behind relative to green OLEDs.However,high-efficiency red emitting materials are still highly desirable due to their wide application in optical communication,information storage,biological imaging,night vision.Many researchers have focused on high-efficiency red emitting OLEDs.Within the traditional fluorescent emitting OLEDs,only 25%singlet excitons can be used,which limits the improvement of device efficiency.In recent years,thermally activated delayed fluorescence(TADF)has emerged.Although TADF material can theoretically realize 100%excitons utilization through reverse intersystem crossing(RISC),there are still some challenges in molecular design,device color purity and stability which makes it difficult for the instant commercialization.By introducing heavy atoms such as iridium and platinum,the phosphorescent materials can realize the radiative transition from triplet excitons(T1)to singlet(S0),and then achieve 100%excitons utilization.Meanwhile,the rigid structure of ligand can reduce non-radiative transitions caused by molecular vibration and rotation,which greatly helps to improve the quantum yield and efficiency of device.Therefore,the commonly used red emitting materials are phosphorescent compounds.Since high concentration of phosphorescent materials in solid state leads to triplet-triplet annihilation(T-T annihilation),the devices are often prepared by a host-guest doping structure.So a suitable host material is essential for high device performance.Herein,we focus on the design,synthesis and study of the host and guest materials in the light-emitting layer for red OLEDs.It is expected that a better device efficiency can be achieved by using rigid Ir(?)complexes.And at the same time,host materials with novel structures are also studied.1.The red emitting complex Ir(mphmq)2(tmd)containing a non-rigid ligand has been reported before.Inspired by this work,the phenyl and the quinoxaline group in the ligands are bonded through an ethyl chain,and the rigid ligands can suppress the vibration and rotation of molecule.The red light-emitting complexes Ir-DHBA and Ir-F-DHBA both have over 28%external quantum efficiency(EQE)when doped in the exciplex host.Besides,the photoluminescence quantum yields(PLQY)of them in dichloromethane solution are 87.8%and 88.3%,respectively.Compared with Ir(mphmq)2(tmd)phosphorescent device where the current efficiency(CE),power efficiency(PE)and EQE are 30.1 cd A-1,32.0 lm W-1 and 24.6%respectively,the devices made by Ir-DHBA and Ir-F-DHBA achieved higher efficiency.Their maximum CE,PE and EQE are 50.0 cd A-1,67.9 lm W-1,25.8%and 47.1 cd A-1,64.6 lm W-1,27.8%,respectively.This result reflects the great potential of developing highly efficient phosphorescent Ir(?)complexes with rigid skeletons.2.Based on the electron-donating iminodibenzyl and triphenylamine groups,we designed and synthesized a series of red light-emitting host materials 7R-1,7R-2 and 7R-3.These three molecules have good thermal stability,and their thermal decomposition temperatures are 445?,446? and 425?,respectively,with the glass transition temperature all higher than 130?.With Ir-F-DHBA as the guest,good device performance was achieved.The electroluminescence peak wavelength of the devices with 7R-1 and 7R-2 as host material is at 600 nm,and the device EQE can reach more than 22%with good device stability.