Preparation And Characterization Of Steric Pyridazine-like Iridium(?) Complexes And Carbazolyl Bipolar Organic Molecules

In the past few years,OLED products have entered people's daily lives with their excellent performances such as thinness,high efficiency,and wide viewing angle.The organometallic complex of iridium?III?is often used as a luminescent material in OLEDs because of its high quantum yield,thermal stability and photostability.The iridium?III?complex is more likely to undergo luminescence quenching under undoped conditions,so it is usually doped into the host material at a suitable concentration to obtain higher efficiency.It has a great influence on the performance of the device,so the precise control of the doping concentration in mass production requires high technical requirements.To solve this problem,it is necessary to develop a luminescent material that is insensitive to the doping concentration.At the same time,the position of the host material in the device is as important as the dopant and has a significant effect on the electroluminescent properties of the device.Among them,bipolar host materials usually contain electron donors and electron acceptors in a single molecule to achieve a balance between hole and electron transport,which can significantly improve the performance of the device.In this context,this paper has studied in the following two aspects:Firstly,in this study,sterically controlled pyridazine ligands were introduced into oxazine ruthenium complexes to synthesize?tpte?₂Ir?pic?and?tpte?₂Ir?tp?to reduce the sensitivity of materials to doping concentration,and also synthesized a sterically hindered oxazine ruthenium complex:?tpp?₂Ir?pic?and?tpp?₂Ir?tp?In contrast,the structure of this series of complexes was confirmed by nuclear magnetic resonance,mass spectrometry and single crystal.Their luminescence in CH₂Cl₂ wavelengths range from 510 nm to 550 nm,all of which are green-emitting.The lifetimes of the complexes?tpte?₂Ir?pic?,?tpte?₂Ir?tp?,?tpp?₂Ir?pic?,and?tpp?₂Ir?tp?were measured to be 1622.0 ns,1984.4 ns,1667.2 ns,and 2032.7 ns,respectively.The?tpte?₂Ir?tp?quantum efficiency can be as high as 79.8%,?tpte?₂Ir?pic?is also 68.5%,and?tpp?₂Ir?tp?and?tpp?₂Ir?pic?and only 60.4%and 55.4%,demonstrating that the introduction of a sterically hindered group effectively increases the quantum efficiency of the complex.And the better performing?tpte?₂Ir?tp?is doped into the material at different concentrations to form a doped device.The?tpte?₂Ir?tp?excitation voltages with doping concentrations of 2%,5%,10%,and 15%are 3.65 V,3.63 V,3.60 V,and 3.63 V,respectively,and the maximum brightness is 88200 cd m^-2,88230 cd m^-2,88363 cd m^-2,88250 cd m^-2,respectively.The maximum current efficiency??_c?of the device with a doping concentration of 10%is 48.4 cd A^-1,and the maximum external quantum efficiency(?_eqe)is 14.1%.It can be seen from the above data that the introduction of a hindered group can reduce the sensitivity of the light-emitting layer to the dopant concentration and exhibit excellent phosphorescent device performance.Secondly,a series of bipolar host materials were prepared by combining the high triplet level and high hole mobility of carbazole with various electron acceptors?amide,1,8-naphthyl anhydride,biimidazole?:4CzppD,EtCzNh,CzBpi,3CzBpi,and their structures were confirmed by nuclear magnetic resonance and mass spectrometry.Their luminescence in CH₂Cl₂ wavelengths range from 425 nm to 465 nm,all of which are blue light luminescence.The fluorescence lifetimes of the 4CzppD,EtCzNh,CzBpi and3CzBpi were 2.4 ns,2.2 ns,0.8 ns and 1.6 ns,respectively.The quantum efficiency of4CzppD was 68.5%.The quantum efficiency of 3CzBpi,EtCzNh and CzBpi were61.2%,40.3%and 25.3%,respectively.4CzppD,EtCzNh,3CzBpi were used as host materials,and compared with the classic host material mCP,Firpic was used as a guest material to make a series of doped devices.The maximum brightness of EtCzNh1 and 3CzBpi devices was 14030 cd m^-2and 11710 cd m^-2,respectively,both higher than mCP(10101 cd m^-2),the maximum?_c and maximum?_eqe of the device,4CzppD(29.3 cd A^-1,21.0%)performance is higher than mCP(25.0cd A^-1,9.6%).The maximum?_c(25.5 cd A^-1)of 3CzBpi is higher than mCP,while the maximum?_eqe?7.4%?is lower than mCP,and the maximum?_c(12.5cd A^-1)of EtCzNh is lower than mCP,but the maximum?_eqe?9.9%?is higher than mCP.These all indicate that 4CzppD,EtCzNh,and 3CzBpi are suitable for use as a light-emitting bipolar host material.It can be seen that the introduction of steric groups can reduce the sensitivity of the luminescent layer to the concentration of dopants,and show excellent properties of phosphorescent devices.It can be seen from the optical physical properties and device properties of 4CzppD,EtCzNh and 3CzBpi that they are suitable for bipolar host materials.