Synthesis And Properties Of Highly Efficient Near-Infrared Light-Emitting Iridium(?) Phosphors

In recent years,near-infrared(NIR)light-emitting materials have attracted much attentions of researchers due to their potential applications toward imaging,telecommunications,night-vision,sensors,health care and energy,et al.Induced by the strong spin-orbit crossing(SOC)from the transition metal ion,transition-metal complexes can harvest both singlet and triplet excitons simultaneously and achieve unity internal quantum efficiency.Thus transition-metal complexes become the main research topics for developing NIR emitters during last 30 years.Among them,platinum(?)complexes have achieved the best performance in NIR organic light-emitting diodes(OLEDs).However,suffering from easy aggregation and relatively long phosphorescence lifetimes,all these Pt(?)complexes doped devices demonstrate severe efficiency roll-off under high current density.In contrast,iridium(?)complexes with a typical octahedral configuration are the most efficient and versatile phosphorescent emitters because they feature relatively short triplet lifetimes and considered as the most promising candidate for NIR emitters.This dissertation reviews the current research progress of NIR emitters and their devices.In view of some key issues of near-infrared(NIR)emitting materials,such as limited materials species,relatively low luminescent efficiencies,serious efficiency roll-off,unclear structure-property relationships,etc.In this dissertation,we designed and synthesized 8novel series including 19 NIR light-emitting iridium(?)complexes bearing rigid fused-heterocyclic ligands.The chemical structures of these Ir(?)complexes were well confirmed via ¹HNMR and ¹³C NMR spectroscopy,MALDI-TOF mass spectrometry,elemental analysis and X-ray single crystal diffraction.thermal properties,photophysical and electrochemical properties are investigated by thermogravimetric analysis(TGA),steady and transient photoluminescent spectrometry,and cyclic voltammetry(CV).The relationship between the molecular sturctures and properties will be revealed.Finally,highly efficient NIR-OLEDs are fabricated through solution-process employing these iridium(?)complexes as guests.These studies demonstrate that the dilemma between longer NIR-emitting wavelength and low efficiency can be solved through decreasing the non-radiative trasition rates by enhancing the rigidity of the cheating ligands.The main research contents and achievements of this dissertation are as follows:1)Two novel iridium(?)complexes,(DPQ)₂Ir(dpm)and(DBPz)₂Ir(dpm)adopt diphenylquinoxaline and dibenzo[a,c]phenazine as the cyclometalating ligands were rationally designed and synthesized to investigate the influence of extendingp-conjugation and enhancing the rigidity of the ligands simultaneously on the photophysical,electrochemical properties and electroluminescent performance.The results indicate that complex(DBPz)₂Ir(dpm)can remain high efficiency though the maximum emission wavelength bathochromic much,resulting from suppressed nonradiative transition rates.Intense NIR excimer phosphorescence is observed in the complex(DBPz)₂Ir(dpm)for the fisrt time.Furthermore,NIR polymer light-emitting diodes(NIR-PLEDs)based on complex(DBPz)₂Ir(dpm)showed a maximum external quantum efficiency(EQE_max)of 6.16%with a radiance(R_max)of up to 29639 m W Sr^-1 m^-2 at 708 nm,which represent the first NIR-PLED with EQE up to 5%based on iridium(?)phosphors.2)Using dibenzo[a,c]phenazine(DBPz)and phenanthro[4,5-abc]phenazine(PPz)as cyclometalated ligands,two deep-red/NIR iridium(?)complexes(DBPz-11,12-DO)₂Ir(acac)and(PPz-11,12-DO)₂Ir(acac)were designed and synthesized.The influence of thep-conjugation and alkoxy flexible side chains on the aggregation behiavior and photophysical properties are studies in detail.All both complexes are strong luminescent in solutions with photoluminesce quantum yields(PLQYs)of 13-27%.As a result,both iridium complexes exhibited high-efficiency DR/NIR electroluminescence in their doped PLEDs.The(PPz-11,12-DO)₂Ir(acac)devices show a maximum EQE of 4.14%with a radiance up to 20981 m W Sr^-1 m^-2 at 724 nm,and the(DBPz-11,12-DO)₂Ir(acac)devices give an increasing EQE of 7.04%with a radiance of 33671 m W Sr^-1 m^-2 at 674 nm.3)To systematically investigate the?-?and p-?conjugation effects on photoluminescent(PL)and electroluminescent(EL)properties,and get high-efficiency near-infrared(NIR)-emitting iridium(?)complexes,in this chapter,two rigid C^N ligands of dibenzo[a,c]phenazine(DBPz)derivatives respectively anchored by flexible side chains of n-octyl and n-octyloxy,and their corresponding iridium(?)complexes of Ir-R and Ir-OR were designed and synthesized.The results turned out complex Ir-OR with p-?conjugation bearing narrower energy gap and much red-shift PL spectrum than complex Ir-R with?-?conjugation.The findings will update the traditional view that the introduction of flexible aliphatic chains was carried out not to tune photophysical properties but to enhance the solubility and suppress detrimental?-?stacking.The solution-processed PLEDs and OLEDs using PVK:OXD-7 and CBP as host respectively are fabricated.The results found out that OLEDs doped with Ir-R show better device performance.The maximum EQE is 6.90%with emission peak at 630 nm.4)Two novel NIR light-emitting phosphors,(Me Ph-Indo Pz)₂Ir(acac)and(^tBu Ph-Indo Pz)₂Ir(acac)constructed from embedded D-A type Indolo[3,2-c]phenazine cyclometalated ligands by ingeniously combine electron-donating indole and electron-withdrawing phenazine through double Michael-type addition,were designed and systematically characterized.Both complexes are highly luminescent in NIR region with photoluminescent quantum yields of 3.5-4.5%.Consequently,efficient EL efficiencies with EQE_max of 2.65%and R_max of 13057 m W Sr^-1 m^-2 with the emission peak at 746 nm was achieved in solution-processed NIR-PLEDs adopting(^tBu Ph-Indo Pz)₂Ir(acac)as guest.5)Four novel NIR-emitting iridium(?)complexes,named as(3,6-DT-DBPz)₂Ir(acac)?(11,12-DT-DBPz)₂Ir(acac)?(3,6-DTPA-DBPz)₂Ir(acac)and(11,12-DTPA-DBPz)₂Ir(acac)with core-shell structure were rationally designed and synthesized by employing highly rigid dibenzo[a,c]phenazine(DBPz)as coordinated core,and hexylthienyl or triphenylamine as peripheral shell anchored in 3,6-or 11,12-positions of DBPz.It is found that core-shell structure,substituted groups and their positions of shells have great influences on properties of these complexes.3,6-substituted complexes are easy to form excimer due to strongerp-pstacking interactions in the condensed states.Strong NIR emissions in 712?741 nm are observed for these core-shell type complexes with quantum efficiency of 18%?30%in solution.Solution-processed NIR-PLEDs based on these phosphors all show good electroluminescent performance with maximum EQE of 6.91%and radiance up to 53611 m W Sr^-1 m^-2.A state-of-the-art external quantum efficiency(EQE)of 13.72%is obtained in the doped OLEDs,which is the highest EQE for NIR-OLEDs using iridium(?)complexes as dopant.Furthermore,undoped OLED exhibited unexpected excimer emission at 788 nm with EQE of 1.01%for the first time.6)Three NIR-emitting iridium(?)complexes with core-shell architecture,termed as(TPA-PPz)₂Ir(acac)?(HT-PPz)₂Ir(acac)and(DPTA-PPz)₂Ir(acac),in which extended?-conjugated phenanthro[4,5-abc]phenazine(PPz)are employed as the rigid core,triphenylamine(TPA),hexylthiophene(HT)and diphenylthiophen-2-amine(DPTA)with different electron-donating ability as flexible peripheral shells,are rationally designed and synthesized.The research results find that the stronger of the electron-donating ability of the shell is,the redder emission of the complexes are.All these complexes show pure NIR emissons with emission peak beyond 770 nm and very little emisison below 700 nm region.Solution-processed PLEDs doped with(TPA-PPz)₂Ir(acac)exhibit high efficiency with maximum EQE up to 3.34%at 768 nm.7)Two iridium(?)complexes named(TBPz-2,7-DC)₂Ir(acac)and(DPIndo Pz)₂-Ir(acac)are constructed by using phenazine derivatives as the building blocks.Afer extending the?-conjugation than DBPz,both complexes all showed emission peak beyond800 nm without any emitted photos power down 700 nm.Thus,both two complexes are truly NIR emitters.Solution-processed PLEDs with emission peaks beyond 840 nm are fabricated and the maximum EQE is 0.02%with maximum emission at 910 nm.8)Employing dipyrido[3,2-a:2',3'-c]phenazine(dppz)as the rigid N^N chelating architecture,two cationic Ir(?)complexes with aggregation-induced phosphorescent emission(AIPE)properties have been developed.Photophysical characterization revealed that these two cationic Ir(?)complexes are almost non-emissive in solutions,in sharp contrast,they exhibit bright emission in the solid states with maximum emission peak reaching to 740 nm and quantum yields of 6?8%,in other words,they are AIPE active.Meanwhile,concentration-dependent PL spectra are observed in the doped films for these two complexes.The doped and nondoped light-emitting devices are fabricated from solution process.Doped device showed better electroluminescent performance than nondoped device with maximum EL peak at 716 nm,maximum EQE of 2.44%,and maximum radiance of 9084?6709 m W Sr^-1 m^-2.