Development And Electroluminescence Property Of Ir³⁺-Containing Metallopolymer Materials With Near-Infrared-Luminescence

Attributing to the characteristics ofl_em>700 nm,low cost and large-size flexible display,near-infrared polymer light-emitting diodes（NIR-PLEDs）fabricated with solution-processing,have been realized with potential applications in the field of night-vision display,optical telecommunication and bio-sensing.Among the fundamental light-emitting materials for NIR-PLEDs,cyclometalated Ir³⁺complexes are highlighted as the“star molecules”,which should be due to their unique photophysical properties such as short phosphorescence lifetime,high luminescence efficiency and range-widen color tuning.So far,despite the significant progress of their doping NIR-PLEDs fabricated with one organic small-molecule or polymer as the host,the blending-induced intrinsic problems of their inferior efficiency and serious efficiency-roll-off suffered from the aggregation-caused quenching,triplet-triplet annihilation and phase separation,have to be confronted.Toward solving that scientific issue,this thesis firstly focused on an approach to covalently-bonding of NIR-emitting cyclometalated Ir³⁺-complexes into the non-conjugated PVK（poly（vinylcarbazole））matrix for NIR-PLEDs.On one hand,single-component binary Ir³⁺-containing metallopolymers with different grafting concentrations as the emitting layers,were constructed.On the other hand,in consideration of the direct carrier-balancing necessary,series of single-component while ternary and bipolar Ir³⁺-containing metallopolymers were obtained from the different co-polymerization methods.Through these innovative ideas,the cyclometalated Ir³⁺-complexes cound be molecularly dispersed into the polymeric matrix for the desirable homogeneity.Moreover,the carriers’transport and balance were also effectively strengthened.Noticeably,the first-example NIR-PLEDs based on Ir³⁺-containing metallopolymers as the emitting layers,were successfully realized,in which,their electroluminescent performance optimized with materials’choice and device design,was further pursed.The main research contents and results were shown as follows:Firstly,the nitrogen heterocyclic ligand Hiqbt（1-（benzo[b]thiophen-2-yl）-isoquinoline）as the C^N cyclometalated main ligand,and the rigidβ-diketone Hdbm（dibenzoylmethan）as the ancillary ligand were adopted to afford a new Ir³⁺-complex[Ir（iqbt）₂（dbm）]characteristic of good NIR-emitting properties(λ_em=713,758（sh）nm,τ=0.24μs,Φ_em=0.15).Meanwhile,using that Ir³⁺-complex as the guest material,its doping NIR-PLEDs were fabricated.Through the investigation of their detailed electroluminescent properties especially after optimizations with device structure and doping concentration,the device doped at a 8 wt%level,exhibited the superior electroluminescent performance(Von=13.9V,λ_EL=708,776（sh）nm,L_e^max=0.105 W·sr^-1·m^-2,η_EQE^max=4.287%)at the cost of significantly serious efficiency-roll-off of about 23%.Secondly,using the newly styryl-modified and[Ir（C^N）2（C’^N’）]-typed cyclometalated Ir³⁺-complex[Ir（iqbt）₂（4-vp-ppy）]as the polymerizible monomer,its single-component and PVK-supported binary Ir³⁺-containing metallopolymers Poly（NVK-co-[Ir（iqbt）₂（4-vp-ppy）]）with NIR-emitting characters were obtained.Encouragingly,the first-example NIR-PLEDs（NIR-PLEDs-II-A～B）using Ir³⁺-containing metallopolymers as the emitting layers,were realized,where,the NIR-PLED-II-B based on Poly（NVK-co-[Ir（iqbt）₂（4-vp-ppy）]）（200:1）as emitting layer in combination with additional electron-transporting and hole-blocking contributions,exhibited the superior electroluminescent performance(V_on=7 V,λ_EL=698,755（sh）nm,L_e^max=0.249W·sr^-1·m^-2,η_EQE^max=2.657%)including the significantly alleviated efficiency-roll-off（11%）in contrast to the corresponding doping one（28%）.Thirdly,in dependence of the newly-synthetic styryl-modified[Ir（C^N）₂（O^O）]-type Ir³⁺-complex monomer[Ir（iqbt）₂（4-vp-dbm）],series of single-component binary Ir³⁺-containing metallopolymers Poly（NVK-co-[Ir（iqbt）₂（4-vp-dbm）]）with typically photo-excited NIR luminescence were further afforded.Similarly,using the Ir³⁺-containing metallopolymers as emitting layers,their grafting-typed NIR-PLEDs-II-A～E were developed.Worthy of notice,the NIR-PLED-II-Cbased on Poly（NVK-co-[Ir（iqbt）₂（4-vp-dbm）]）（75:1）was the typical NIR-PLED,exhibiting theλ_EL=704 nm,and the superior performance:V_on=10 V,L_e^max=0.185 W·sr^-1·m^-2,η_EQE^max=1.916%and weaker efficiency-roll-off（about 22%）were also confirmed in comparison with the doping one（efficiency-roll-off of up to 26%）.At last,from the viewpoint of the lowest-cost with single-layer fabrication,single-component while ternary bipolar（PVK acting as hole-transport and 4-vp-Hpbd（2-（4-t-butylphenyl）-5-（4-vinylbiphenyl-4’-yl）-1,3,4-oxadiazole）functioning as electron-transport） Ir³⁺-containing metallopolymers Poly（NVK-co-[Ir（iqbt）₂（4-vp-dbm）]-co-（4-vp-pbd））co-grafted with the chromophore[Ir（iqbt）₂（4-vp-dbm）]and the styryl-modified electron-transporting organic monomer4-vp-Hpbd into the PVK matrix,were obtained by the traditional free radical polymerization.Moreover,among their grafting NIR-PLEDs-I-A～C,NIR-PLED-I-A with a feed ratio 75:1:1 showed the superior electroluminescent performance:Von=12.7 V,λ_em=710 nm,L_e^max=0.224 W·sr^-1·m^-2,η_EQE^max=2.626%and weak efficiency-roll-off（about 16%）.Meanwhile,to improve the uniformity of Ir³⁺-containing metallopolymers with narrower molecular-weight distributions,a controlled reversible addition-fragmentation chain transfer（RAFT）co-polymerization method was adopted instead,giving another series of single-component ternary bipolar Ir³⁺-containing metallopolymers CPDB-[g]-Poly（NVK-co-[Ir（iqbt）₂（4-vp-dbm）]-co-（4-vp-pbd））.As expected,among their grafting NIR-PLEDs-II-A～C,NIR-PLED-II-B with a feed ratio75:1:5 showed the significantly improved performance:V_on=10 V,λ_em=708,768（sh）nm,L_e^max=0.341 W·sr^-1·m^-2,η_EQE^max=2.834%,and negligible efficiency-roll-off（about 13%）.