Synthesis And Electroluminescence Properties Of Deep Red-emitting Iridium Complexes Based On Benzofuran-isoquinoline

Due to the enhanced spin-orbit coupling(SOC)effect of heavy metal atoms in iridium complexes,singlet(S₁)and triplet(T₁)excitons can be fully utilized in phosphorescent organic light-emitting diodes(OLEDs),and 100%internal quantum efficiency(IQE)can be theoretically achieved,Meanwhile,the iridium complex has the advantages of easily tunable emission colors,strong structural modifiability,high efficiency,high brightness and stable chemical properties,which make them more attractive in the field of OLEDs.At present,the performance of OLEDs based on green and blue iridium complexes have basically met the market requirements,but high-performance red to near-infrared iridium complexes are still scarce.In this thesis,a series of deep red phosphorescent iridium complexes based on benzofuran-isoquinoline were designed and synthesized,and their photophysical,thermal stability,electrochemical and electroluminescence properties were studied in detail.The specific research contents are as follows:(1)The phenyl on 1-phenylisoquinoline was replaced by 5-methylbenzofuran-7-yl,at the same time,two alkyl substituents(isopropyl and isobutyl)were introduced at the 6#position of isoquinoline,and 3,7-diethyl-4,6-nonanedione was used as an auxiliary ligand to design and synthesize two deep red-emitting iridium complexes Ir1 and Ir2 with photoluminescence peaks around 626 nm.The two iridium complexes have high photoluminescence quantum yields(PLQYs,around 74%)and low phosphorescence lifetimes(?,around 0.7?s).Phosphorescent OLEDs were prepared by doping complexes Ir1 and Ir2 as guest luminescent materials into the host material 4,4'-N,N'-dicarbazole biphenyl(CBP)at a concentration of 5 wt%.Devices based on complexes Ir1 and Ir2exhibit maximum external quantum efficiencies(EQEs)as high as 14.1%(Device 1)and13.3%(Device 2),far exceeding those based on Ir(piq)₂(acac)also using CBP as a host material of the OLED with the maximum EQE(9.71%).In addition,the electroluminescence peaks of Device 1 and Device 2 are located near 637 nm,and the turn-on voltages(V_ons)are 2.4 V and 2.7 V,respectively,and their maximum brightness are6428 cd·m^-2 and 4585 cd·m^-2,respectively,the maximum current efficiencies(CEs)are all7.0 cd·A^-1,their maximum power efficiencies(PEs)are 7.9 lm·W^-1 and 7.8 l lm·W^-1,respectively,and the CIE coordinates are all(0.69,0.30).(2)On the basis of complexes Ir1 and Ir2,the iridium complexes Ir3 and Ir4 were synthesized by introducing isobutyl at the 2#position of benzofuran.Their photoluminescence peaks are both located at 639 nm,and PLQY values are around 66%and?values are around 1?s.Device 3 and Device 4 were prepared by doping the complexes Ir3 and Ir4 as guest luminescent materials into CBP at a concentration of 5 wt%.Their electroluminescence peaks are located near 648 nm,and their V_ons are both at 2.6 V,the maximum brightness are 3296 cd·m^-2 and 3426 cd·m^-2,respectively,the maximum EQEs are 12.4%and 11.5%,respectively,the maximum CEs are 4.2 cd·A^-1 and 3.6 cd·A^-1,respectively,the maximum PEs are 5.1 lm·W^-1 and 4.7 lm·W^-1,respectively,and the CIE coordinates are(0.68,0.30)and(0.69,0.29),respectively.Comparing the above two types of iridium complexes,the spectrum can be red-shifted by introducing an electron-donating isobutyl group on benzofuran,and the luminous efficiency of OLEDs based on complexes Ir1 and Ir2 is better than that of complexes Ir3and Ir4,because the complexes Ir3 and Ir4 have longer emission wavelengths and slightly lower PLQY values,but overall,the luminescence efficiencies of OLEDs based on the four complexes are better than those of the complex Ir(piq)₂(acac).