Synthetic Design And Optoelectronic Property Of Near-infrared-emitting Ir³⁺/Pt²⁺-Complexes

With the progressive advance of near-infrared organic light-emitting diodes?NIR-OLEDs?potentially utilized in optical telecommunication,national defense,information-security and night-vision displays,a number of bis-and tris-cyclometalated iridium???complexes[Ir?C^N?₂?L^X?]and[Ir?C^N?₃]have been developed,due to the ir attracting characters of easily-gone synthesis and purification,color-tuning,high quantum yield,relatively short triplet lifetime and good stability.To date,despite efforts to NIR-OLED/PLED based on some bis-and tris-cyclometalated iridium???complexes,the‘bottleneck'problems of the low NIR color-purity and the inferior electroluminescent performance should be so lved.Towards this issue,this thesis devoted to the molecule-desgned strategy,in which,the involvements of largep-conjugated C^N-cyclometalted main ligands and/or functionalized auxiliary ligands were considered to affort novel iridium???complexes with restrictive NIR luminescence and good efficiency.Moreover,in dependence on the time-dependent density functional theory calculation?TD-DFT?,their NIR-phosphorescent triplet mechanism was revealed,and their thermal and electrochemical properties were also investigated.Meanwhile,Using some selected Ir³⁺-complexes with excellent NIR photoluminescence as the guest materials,their doping NIR-PLEDs with good electroluminescent performance were realized.Noticeably,the detailed correlation between the molecular structure and the photo-electroluminescence was further concerned.The contents and the results are listed as follows.Firstly,the usage of the largep-conjugated C^N main ligand was for its iridium???complexes.Taking the ligand Hdpbq?2,3-diphenylbenzo[g]quinoxaline?as the C^N-cyclometaltedmainligandandthe?-diketoneHdbm??Z?-3-hydroxy-1,3-diphenylprop-2-en-1-one?or the imidazole-diketone Htfhe-pmp?4-?2,2,2-trifluoroacetyl?-1-phenyl-3-methyl-1H-pyrazol-5?4H?-one?orHdmb-pmp?4-?3,3-dimethylbutanoyl?-1-phenyl-3-methyl-1H-pyrazol-5?4H?-one?as the ancillary ligand,respectively,three novel iridium???complexes with[Ir?dpbq?₂?O^O?]-heteroleptic?1-3?characters were successfully obtained according to the conventional synthetic method.Besides the high thermal stability and the desirbale electrochemical property,all of them exhibited the typical NIR luminescence with color-purity over 99.5%,in which,the emissive wavelength peaking at 780 nm,the quantum yield(?37?_PL)of 1.82-2.50%and the phosphorescence lifetime?t?in the range of 0.28-0.32ms were obtained,respectively.Their density functional theory?TD-DFT?calculate absorptions should exhibit the mixed^1,3LLCT/^1,3MLCT transitions,and ³MLCT transitions are responsible for the NIR-emitting phosphorescence of the Ir³⁺-complexes 1-3.Secondly,using the largerp-conjugated Htpbz?tribenzo[a,c,i]phenazine?as the C^N main ligand and every Schiff-base-typed ligand(HL^1-4)as the N^O-ancillary ligand,four new[Ir?tpbz?₂?N^O?]-heteroleptic?4-7?complexes were developed.Following on their characterization and photo-physical properties'investigation,the four iridium???complexes are characteristic of restrictive NIR-luminescent nature.O n one hand,their emissive wavelength peaking at 835 nm was distinctively red-shifted in comparison with that?780 nm?of[Ir?dpbq?₂?O^O?]-heteroleptic complexes 1-3.O n the other hand,besides the similar good thermal and electrochemical stabilities,the quantum yields(?37?_PL)of 1.14-2.08%and the phosphorescence lifetimes?t?of 0.18-0.25ms for the compounds 4-7,respectively.Their TD-DFT calculate absorptions exhibit the mixed ^1,3LLCT/^1,3MLCT transitions,and³LC/³MLCT transitions are responsible for the NIR-emitting phosphorescence of the four Ir³⁺-complexes 4-7.Thirdly,based on the iridium???complex[Ir?dpqx?₂?PBI?]?8?or[Ir?iqbt?₂?PBI?]?9?as the precusor,their hetero-bimetallic Ir³⁺-Pt²⁺-complexes were derived.Through the Hdpqx?2,3-diphenylquinoxaline?or the Hiqbt?1-?benzo[b]thiophen-2-yl?-isoquinoline?as the C^N main ligand and the HPBI?2-?pyridin-2-yl?-1H-benzo[d]imidazole?as the N^N-ancillary ligand,two new iridium???complexes[Ir?dpqx?₂?PBI?]?8?and[Ir?iqbt?₂?PBI?]?9?were afforded,respectively.After further introducing the Pt?II?ion into the?PBI?^-moiety,another two unprecedented heterometallic binuclear Ir³⁺-Pt²⁺-complexes[Ir?dpqx?₂?PBI?Pt?acac?]?10?and[Ir?iqbt?₂?PBI?Pt?acac?]?11?are obtained,respectively.The results of their photo-physical properties showed:the emission peaked(l_PL)and PL quantum yield(?37?_PL)of640 nm and 0.86%for the Ir³⁺-complex 8,690 nm and 0.69%for the Ir³⁺-complex 9,693 nm and 8.37%for the Ir³⁺-Pt²⁺-complex 10 or 682 nm and 6.34%for the Ir³⁺-Pt²⁺-complex 11,respectively.As a result,the post-modification with the cyclometallated Pt?II?ion gave an innovative approach to cor-tuning.Their TD-DFT calculate absorptions should exhibit the mixed ^1,3LLCT/^1,3MLCT transitions,and ³LC/³MLCT transitions are responsible for the phosphorescence of the complexes 8-11.Finally,each of these compounds 8-11 was applied as the guest of the corresponding emitting layer to successfully afford desirable NIR-PLEDs.Through the optimized device structure configured with ITO/PEDO T:PSS?40 nm?/PVK?30%?:complex 8/9/10/11?40%?:OXD-7?30%??80 nm?/TPBi?30 nm?/LiF?1 nm?/Al?120 nm?,series of devices PLED-I,NIR-PLED-II,NIR-PLED-?,NIR-PLED-IV were realized.Their electroluminescent properties showed that,the maximum emission wavelength(l_EL),maximum brightness(L_e^max)or irradiance(R^{m ax})and maximum external quantum efficiency(?_EQE^{m ax})were valued with 650 nm,42.88 cd/m²,5.51%for the PLED-I;692 nm,9.62 W/sr·cm²,2.33%for the NIR-PLED-II;693 nm,47.84 W/sr·cm²,6.80%for the NIR-PLED-? and 686 nm,18.01W/sr·cm²,8.11%for the NIR-PLED-IV,correspondingly.Noticeably,the formation of hetero-binuclear Ir³⁺-Pt²⁺-complexes was significantly beneficial to color-tunable NIR-PLEDs with better electroluminescent performance,from which,to the best of our knowledge,the first example NIR-PLEDs fabricated with Ir³⁺-Pt²⁺-heterometallic binuclear complexes were developed.