Synthesis Of Novel Ruthenium(Ⅱ)/Iridium(Ⅲ) Complexe-Based Luminescent Probes And Their Application In The Detection Of Benzimidazole Pesticides

Ruthenium（Ⅱ）and iridium（Ⅲ）complexes,a type of small molecular luminophore,have excellent photophysical,photochemical and electrochemical properties,further more,they have the advantages of easy modification of the structure and adjustable luminescence properties.Therefore,ruthenium（Ⅱ）and iridium（Ⅲ）complexes can be used in electrochemiluminescence and phosphorescent probes.In this paper,through the molecular structure design of the ligands,a variety of novel ruthenium（Ⅱ）and iridium（Ⅲ）complexes were synthesized for the development of excellent electrochemiluminescence luminophores.What’s more,an iridium（Ⅲ）solvent complex was synthesized as phosphorescent probe for the detection of benzimidazole pesticides.Firstly,three new ruthenium（Ⅱ）complexes containing an N-heterocyclic carbene（NHC）ligand（Ru NHC）have been successfully synthesized in this work.Due to the incorporation of NHC ligands,Ru NHC complexes exhibit NIR phosphorescence and electrochemiluminescence emission with the peak wavelength near 800 nm.In addition to the advantages of the lower-charge main motif（+1）,the much lower oxidation potentials,and the longer metal to ligand charge transfer（MLCT）absorption bands,most importantly,these Ru NHC complexes show higher,or at least comparable,ECL efficiency compared with Ru（bpy）₃²⁺after optimizing the co-reactants.In this work,the effects of different substituents on Ru NHC complexes were also investigated through DFT theoretical calculations and other experiments.In addition,two novel heteroleptic iridium（Ⅲ）complexes,Ir NHC-S and Ir NHC-SO₂ were designed and synthesized,in which dibenzothiophene and derivatives-substituted imidazolium salts as NHC precursors have been designed as novel C^C*bidentate main ligands.The emission peaks of these two NHC-based iridium（Ⅲ）luminophores are centered at ca.530 nm and the PL quantum efficiency of Ir NHC-S and Ir NHC-SO₂ are up to 79.8%and 19.2%respectively.Beside excellent photophysical properties,CV results revealed that these two novel iridium（Ⅲ）complexes comprising N-heterocyclic carbene main ligands exhibited comparatively low oxidation potential（<0.5 V vs Fc/Fc⁺）.Most importantly,ECL performances of these two novel NHC-based iridium（Ⅲ）complexes under different electrochemical modes have also been thoroughly investigated for the first time in this work.The ECL results demonstrated that Ir NHC-S and Ir NHC-SO₂ with TPA as co-reactant could reach the maximum ECL intensity below 1 V vs Fc/Fc⁺.Finally,an iridium（Ⅲ）solvent complex（Ir-probe）has been synthesized as a new phosphorescent probe to detect benzimidazole pesticides.Ir-probe is weakly luminescent in PL analysis due to the presence of two weakly bound solvent ligands.However,when Ir-probe bind covalently to thiabendazole（TBZ）or carbendazim（CBZ）through a ligand substitution reaction with the solvent ligands,the phosphorescent emission intensity of Ir-probe increased significantly.The results show that Ir-probe has the advantages of good selectivity and high sensitivity in response to TBZ and CBZ,and the probe has also successfully been employed to detect TBZ and CBZ residues in real samples.In addition,thin-layer chromatography（TLC）method has been employed to investigate the intrinsic PL“turn-on”mechanism via analyzing the compounds formed in the reaction between Ir-probe and TBZ/CBZ in this work.