Synthesis And Properties Of Phosphorescent Sensing Materials Based On Efficient Ir(Ⅲ) Complexes

Iridium complexes were used in various fields such as organic light-emitting diodes（OLED）,cell imaging,and chemical sensing,due to their high luminescence efficiency,short excited-state lifetime,large Stokes shift,and tunable emission color.In this paper,several iridium complexes with different luminescent colors are designed and synthesized,the relationship between the structure and properties of the complexes is studied,and the application of iridium complexes in the field of chemical sensing is explored.This study provides a feasible way for designing and synthesizing phosphorescent sensing materials based on highly efficient iridium complex.The specific research are as follows:（1）A cationic iridium cyclometalated complex[（3F-piq）₂Ir（dtb-bpy）]⁺（PF₆^-）（Ir1）with 1-（3-fluorophenyl）isoquinoline（3F-piq）as a cyclometalated ligand,4,4’-di-tert-butyl-2,2’-bipyridine（dtb-bpy）as a neutral ligand and hexafluorophosphate as an anion has been synthesized successfully.X-ray crystallographic analysis displays that the iridium center adopts a distorted octahedral coordination geometry.Upon excitation at327 nm,the complex Ir1 exhibit strong red phosphorescence(λ_em=590 nm)with quantum efficiencies of 55%in oxygen-free dichloromethane solution at room temperature.Electrochemical study shows a quasireversible oxidation with potentials at 0.80～1.50 V（vs.Ag⁺/Ag）,which is attributed to the redox process of Ir³⁺/Ir⁴⁺.Theoretical calculation shows that the highest occupied molecular orbital（HOMO）mostly distribute over the d orbitals of the iridium atom（45.19%）and the main ligand（52.18%）,and the lowest unoccupied molecular orbital（LUMO）is mainly localized on the neutral ligand（84.89%）.（2）Two cationic iridium（III）complexes[Ir（L1）₂（db-bpy）]⁺（PF₆^-）（Ir2）and[Ir（L2）₂（db-bpy）]⁺（PF₆^-）（Ir3）with 4,4’-dibromo-2,2’-bipyridine（dbr-bpy）as neutral ligand,6-phenylnicotinaldehyde（L1）and 6-（4-trifluoromethylphenyl）pyridine-3-carbaldehyde（L2）as cyclometalated ligands were synthesized.Their photoluminescence spectra were influenced by trifluoromethyl（CF₃）in the cyclometalated ligands,givingλ_maxvalues in the range of 530～584 nm with quantum yields（Φ）of 0.49～0.66 and lifetimes of 1.6～3.3μs.DFT calculations demonstrate that both complexes exhibit ligand-to-ligand charge transfer（LLCT）and metal-to-ligand charge transfer（MLCT）excited state character from the cyclometalated ligand and Ir（III）center to the neutral ligand.The study of cyclic voltammograms and theoretical calculation indicated the introduction of CF₃moieties into the cyclometalated ligands can reduce the HOMO energy,and made the oxidation potential shift towards the anode.The two complexes displayed significant phosphorescence quenching upon binding to Cys and the binding stoichiometry was approximately 1:2 with the detection limit of 3.51×10^-5M and 1.85×10^-5M,respectively.Upon the addition of OH^-into the solution of Ir3 in DMSO/H₂O（7:3）,OH^-replaced the bromine substituents on the neutral ligand of Ir3,resulting in a blue-shift of the emission peak.The luminescence color of the complex Ir3 changed from yellow to green and complex Ir3 showed a 5-fold enhanced emission at alkaline environment when compared to neutral p H.（3）Six iridium complexes Ir4-Ir9 were synthesized using L-valine and L-alanine as auxiliary ligands and fluorine-substituted ring metal ligands.Photophysical experiments show that the emission wavelengths of complexes Ir6 and Ir7 are blue-shifted to 492 and464 nm,respectively,relative to the emission wavelength of Ir4（514 nm）,and the emission wavelengths of complexes Ir8 and Ir9 are blue-shifted to 493 and 464 nm,respectively,relative to the emission wavelength of Ir5（517 nm）.Theoretical calculations show that when fluorine groups are introduced,the HOMO levels of the complexes Ir7 and Ir9 drop to-5.63 and-5.64 e V,respectively,while the LUMO levels are almost unchanged.The sensing experiments of Cu²⁺show that the complexes Ir4-Ir9 have phosphorescence quenching response to Cu²⁺,and have high selectivity to Cu²⁺,and the recognition of Cu²⁺is less disturbed by other metal ions.The detection limits of Ir4-Ir9 for Cu²⁺were calculated by the linear relationship between the emission spectrum intensity of the complexes and the added Cu²⁺concentration.The detection limits of Ir6 and Ir8 were6.5×10^-7M and 6.0×10^-7M.