Syntheses,Structures And Properties Of Novel Red To Near-infrared Phosphorescent Iridium Complexes

In recent years,Organic luminescent materials play a more and more important role in the fields of display,lighting,sensing,medical and energy.Phosphorescent organic materials based on transition metal complexes as luminescent materials have drawn great interest because the strong spin-orbit coupling(SOC)and fast intersystem crossing could lead to a harvest of both singlet and triplet excitons,achieve 100% internal quantum efficiency theoretically.Up to date,the efficiencies and lifetimes of green,yellow phosphorescent materials have been basically able to meet the requirements for practical application.However,highly efficient and stable red to near-infrared phosphorescent emitters are still under developed.Iridium(III)complexes gradually become an important research direction for designing high efficiency red to near-infrared phosphorescent materials now because they usually possess relatively short triplet lifetimes,high quantum yields,tunable emission color,synthesis and purify easily,splendid thermal and electrochemical stability.In this dissertation,a series of novel red to near-infrared phosphorescent iridium complexes containing amidine or guanidine-based ligands were designed and synthesized,and we investigated their single crystal structure,thermal properties,photophysical properties,electrochemical properties,theoretical calculations,carrier transport properties.And a series of red to near-infrared phosphorescence electroluminescent devices were fabricated using these complexes as guest materials.The relationship between structure and properties of this series of iridium complexes was discussed.1.In chapter II,two new deep-red Iridium(III)complexes named SFPIQBA and DFPIQBA,comprising 1-(4-fluorophenyl)isoquinoline,1-(2,4-difluorophenyl)isoquinoline as first ligand and N,N’-diisopropylbenzamidinate(dipba)as ancillary ligand are designed,synthesized and characterized.Both of them have great thermal and electrochemical stability.Given the unique four-membered Ir-N-C-N backbone built by the metal center and the ancillary ligand,both phosphors achieve significant improvement for their comprehensive optoelectronic characteristics.Compared with the classical ancillary ligand acetylacetone,amidino-based ligand can effectively enhance the HOMO level of the complex and reduce the energy gap,which enables complex to achieve deep red light emission.Density function theory(DFT)calculations show their clearly distinct electron density distributions of the HOMO/LUMO orbitals,indicating that they have bipolar carrier transport ability which proved by TOF measurement.Both new phosphors present deep-red emission(around 640 nm)with high PLQYs and short excited-state lifetimes.The phosphorescent organic light emitting diodes(PhOLEDs)based on SFPIQBA and DFPIQBA realize deep-red emitting with stable CIEx,y coordinates of(0.70,0.30)and(0.69,0.31).The maximum external quantum efficiencies(EQE)and power efficiency(PE)values of 15.4%/9.3 lm W-1 and 16.7%/10.4 lm W-1 respectively,which maintain such high levels as 10.6%/3.5 lm W-1 and 10.8%/3.6 lm W-1 at the practical luminance of 1000 cd m-2.2.In chapter III,we synthesized a novel deep red phosphorescent iridium complex PIQBA,using 1-phenylisoquinoline as the first ligand and amidino-type dipba as the ancillary ligand.PIQBA has a polymorphism phenomenon which was rarely reported in iridium complexes.Polymorphism A shows a near-infrared emission of 730 nm and polymorphism B shows a deep red emission of 680 nm.The relationship between the structure and properties of two polycrystalline crystals was discussed by combining the intermolecular interactions,packing structure,molecular configuration of different polymorphism crystals.And the influence of electron-rich double N coordination on the frontier orbital of iridium complex was also studied.Theoretical calculation shows PIQBA has obviously delocalized electron cloud distribution,indicating that it has both hole and electron transport abilities which proved by TOF measurement.PIQBA exhibited excellent thermal stability which is good for vacuum evaporation devices fabrication.Phosphorescent organic electroluminescent device based on PIQBA shows a maximum emission of 676 nm,the maximum EQE/PE of device was 10.7%/1.9 lm W-1,the CIE coordinate was(0.71,0.28)and the maximum brightness reached 5909 cd/m2.Excellent red color purity and spectral stability of devices were both achieved.3.In chapter IV,four new red to near-infrared phosphorescent Iridium complexes named BZQPG,PIQPG,SFPIQPG,DFPIQPG were synthesized by comprising 7,8-benzoquinoline and 1-phenylisoquinoline derivatives as first ligand,N,N′-diisoproguanidinate(dipig)as ancillary ligand.All these compounds have more red-shift emission spectra,shorter phosphorescent lifetimes and higher phosphorescent quantum yields than the previously discussed complexes containing amidino-based ligand,The theoretical calculations show that guanidino-type dipig ligands have more stronger electron-donating ability than amidino-type dipba ligand,resulting stronger coordination ability with the iridium atoms,rising the HOMO energy level and reduce the energy gap.Thus can reach a more red-shift emitting and reduce the vibration energy loss.These four compounds also have great thermal and electrochemical stability,efficient bipolar transport ability.Phosphorescent organic electroluminescent devices based on these compounds show stable and efficient EL performance.The maximum EQEs of BZQPG,PIQPG,SFPIQPG and DFPIQPG devices were 27.3%,12.1%,16.3% and 16.7%,the maximum emission wavelength of these devices were 592 nm,684 nm,656 nm and 652 nm,respectively,all devices exhibited good spectral stability and low efficiency roll-off.4.In chapter V,three new near-infrared phosphorescence complexes named MPIQBA,MPIQPG and CF3 PIQPG were synthesized by simple substitution of first ligand 1-phenylisoquinoline.The emission wavelengths of these iridium complexes were extended to the near-infrared region without introducing a larger π-conjugated group.Thus adverse effect such as the efficiency quenching caused by the conjugation aggregation can be effectively avoided.And the small molecular weight could be favorable for vacuum evaporation devices fabrication.Theoretical calculations show their HOMO and LUMO orbits are distributed on separate groups.TOF measurements show that they have bipolar carrier transport ability.Thermal and electrochemical measurements show that all these three compounds have good thermal and electrochemical stability.These complexes possessed very good EL performance.The maximum emission wavelength of MPIQBA device was 688 nm,the CIE color coordinate was(0.71,0.28)and the maximum external quantum efficiency was 12.0%;the maximum emission wavelength of MPIQPG device was 692 nm,the CIE color coordinate was(0.71,0.28)and the maximum external quantum efficiency was 11.6%;the maximum emission wavelength of CF3 PIQPG device was 692 nm,the CIE color coordinate was(0.71,0.28),and the maximum external quantum efficiency of the device was 6.3%.The brightness of all these devices has realized more than 1500 cd/m2.In summary,we synthesized a series of novel red to near-infrared phosphorescent iridium complexes.The innovation of our work is the introduction of amadinate and guanidinate ancillary ligand.Compared with the traditional acetylacetone-based ligand,these novel iridium complexes have more electron-rich double N-coordinated structure,which can effectively stabilize the trivalent metal iridium atoms.And the metallacycle formed by Ir··N··C··N four atoms has a stronger rigidity,which can reduce unnecessary vibration energy loss,achieve better phosphorescence quantum yield.Theoretical calculation results show that the amidine or guanidine-based ligands can largely involve in the frontline orbitals composition of these iridium complexes,which caused the rise of the HOMO energy level,reduce the energy gap.Carrier mobility measurements show this series of iridium complexes have very high electron and hole mobility,which can effectively reduce triplet-triplet quenching at high current density and high electroluminescence in phosphorescent devices.And high efficiency PHOLEDs of these complexes have been fabricated.The relationship between structures and properties has been carefully investigated,and more importantly,it injects new energy to realize the simple,high-efficiency and high-quality deep-red PhOLEDs.