Synthesis Of New Phosphorescent Iridium Complexes And Their Application In Ion Detection

Cu²⁺and Zn²⁺play important roles in humans.Abnormal concentration of Cu²⁺and Zn²⁺can lead to neurodegenerative diseases,gastrointestinal disorders,and liver or kidney damage.Therefore,the qualitative and quantitative detection of Cu²⁺and Zn²⁺is of great significance to human health.Iridium complexes have the characteristics of high luminescence efficiency,tunable color,and relatively long excited state lifetime,which have potential application prospects in the field of phosphorescence sensing.In this paper,six dinuclear iridium complexes and two mononuclear iridium complexes were synthesized,and the photophysical and electrochemical properties of these iridium complexes and their applications in metal ion detection were investigated.The specific research contents are as follows:（1）Three dinuclear iridium complexes with 2,5-bis（1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl）furan（H₂bfip）as the neutral bridged ligand,2-（4-（trifluoromethyl）phenyl）pyridine（cf₃ppy）and1-（4-（trifluoromethyl）phenyl）isoquinoline（cf₃piq）as cyclometalated ligands,[（cf₃ppy）₂Ir（H₂bfip）Ir（cf₃ppy）₂]（PF₆）₂（Ir1）,[（cf₃piq）₂Ir（H₂bfip）Ir（cf₃piq）₂]（PF₆）₂（Ir2）and[（cf₃piq）₂Ir（H₂bfip）Ir（cf₃ppy）₂)]（PF₆）₂（Ir3）were synthesized.By changing the structure of the cyclometalated ligands,they presented decent yellow to orange emission with quantum yields of 0.44-0.68,the complex Ir2 has the highest quantum yield 0.68.The lifetimes of complexes Ir1-Ir3 are 1.8-2.3μs,which are all in the microsecond,indicating that complexes Ir1-Ir3 have phosphorescence properties.Three complexes all showed quenched phosphorescence response to Cu²⁺with high selectivity and strong anti-interference ability over other metal ions.The detection limit was as low as 1.1×10^-7M.The binding stoichiometry of these dinuclear complexes to Cu²⁺was confirmed to be 1:1 by the titration data and Job plot analysis.Cu²⁺is coordinated with nitrogen,oxygen atoms on bridging ligands and two nitrate ions for the significant reasons of chemical sensing with Cu²⁺by iridium complexes,which is further confirmed by¹H NMR and ESI-MS spectra.（2）Three dinuclear iridium complexes Ir4-Ir6 with 2,5-bis（1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl）thiophene（H₂btip）as the neutral bridged ligand,the cyclometalated ligands still use cf3 ppy and cf3 piq,[（cf₃ppy）₂Ir（H₂btip）Ir（cf₃ppy）₂]（PF₆）₂（Ir4）,[（cf₃piq）₂Ir（H₂btip）Ir（cf₃piq）₂]（PF₆）₂（Ir5）and[（cf₃piq）₂Ir（H₂btip）Ir（cf₃ppy）₂)]（PF₆）₂（Ir6）were synthesized.The luminescence intensity of the complex Ir4 is weak,while complexes Ir5 and Ir6 both exhibit strong orange-red emission.Their maximum emission peaks are blue-shifted to different degrees compared with the same series of Ir2 and Ir3.The quantum efficiencies of Ir5 and Ir6 are 0.47 and 0.26,respectively,and the lifetimes are 1.6μs and 1.4μs,respectively.The complexes Ir5 and Ir6 produce phosphorescence quenching effect on Cu²⁺with specific recognition and can be used as quenched phosphorescence probes for Cu²⁺The binding stoichiometry of complexes Ir5 and Ir6 to Cu²⁺was 1:1,and the detection limits were 5.3×10^-6M and 8.4×10^-6M,respectively.（3）Two mononuclear iridium complexes with 6-phenylnicotinaldehyde（L1）and6-（4-（trifluoromethyl）phenyl）pyridine-3-carbaldehyde（L2）as cyclometalated ligands,and bis（diphenylphosphonamide）amide as auxiliary ligands,（L1）₂Ir（tpip）（Ir7）and（L2）₂Ir（tpip）（Ir8）were synthesized.The complexes Ir7 and Ir8 both exhibit orange-red light emission with quantum efficiencies of 0.32 and 0.57,respectively,and their lifetimes are in the microsecond range,making them two very good phosphorescent materials.Over the introduction of electron-absorbing groups in the cyclometalated ligands,the emission peak and absorption peak in the low-energy region of complex Ir8 are blue-shifted and the oxidation potential is increased compared with complex Ir7.Theoretical calculations show that the introduction of electron-withdrawing groups can reduce the HOMO energy level and increase the energy gap between HOMO and LUMO of the complexes,thereby causing changes in the luminescence properties of the complexes.The complexes Ir7 and Ir8 displayed significant phosphorescence enhancement for detecting Zn²⁺with a 1:1 stoichiometry.The corresponding detection limits were determined to be 5.7×10^-7M and 3.6×10^-7M,respectively.