Construction And Optoelectronic Properties Of Benzimidazole-ancillary Iridium (?) Complexes With Near-infrared Luminescence

Near infrared organic or polymer light-emitting diodes(NIR-OLEDs/PLEDs)have potential value for applications in night vision display,communication and information security,etc.However,NIR-OLEDs/PLEDs based on phosphorescent iridium(III)complex materials still have some problems such as low external quantum efficiency and serious efficiency roll-off especially at high current density.In order to solve these problems,herein,two series of novel iridium(III)complexes were prepared from the perspective of controlling near-infrared luminescence and improving photoluminescence quantum yield.Meanwhile,the PLEDs devices with excellent optoelectronic properties were prepared by applying some of the iridium(III)complexes as guest with excellent photo-physical properties.Firstly,a series of bis-heteroleptic iridium(III)complexes[Ir(C^N)₂(N^O)](1-3)were synthesized by using large conjugated Hdpqx(2,3-diphenylquinoxaline),Hiqbt(1-(benzo[b]thiophen-2-yl)-isoquinolinate)or Hdpbq(2,3-diphenylbenzo[g]quinoxaline)as the C^N major ligands and Hpbi(2-(1-H-benzimidazol-2-yl)phenol)as the N^O auxiliary ligand to promote electronic transmission,respectively.The experiment and quantum chemical calculations show that the near-infrared phosphor redshift of the complexes 1-3with emission wavelengths at 707,712 and 807 nm is achieved by changing the heterocyring of the main ligand and adding the conjugated benzene ring of the main ligand.And the photoluminescence quantum yield(?_PLQY=0.26,0.21,0.03)decreases accordingly.Next,a series of tris-heteroleptic iridium(III)complexes[Ir(C^N¹)(C^N²)(N^O)](4-6)were synthesized by using Hiqbt as the C^N¹ ligand,Hbtp(2-(2-pyridyl)benzothiophene),Hdpqx or Hdpbq as the C^N² ligand and Hpbi as the N^O ancillary ligand,respectively.The experiment and quantum chemical calculations show that regulating the lowest triplet excited state energy level of the complexes 4-6 not only leads to regulation of near-infrared luminescence with emission wavelength at 714,715 and 815 nm,but also reduces the non-radiative transition pathway,which makes the efficient interfragment charge transfer,thus increasing the photoluminescence quantum yield(?_PLQY=0.20,0.24,0.04).The design and analysis of these molecular structures provide a new direction for the development of iridium(III)complex with excellent near-infrared photo-physical properties.Finally,device structure with matching energy level was designed,and the doped PLEDs-D1-D4 were prepared by using spin-coating procedure based on the complexes 1,2,4 and5.The PLEDs-D1-D4 have excellent external quantum efficiency and neligible efficiency-roll-off.Specially,thanks to the high ptotoluminescence quantum yield of the complex 5,the maximum external quantum efficiency of the PLEDs-D4 at 706 nm reaches 6.10%.