Synthesis And Properties Of Ion-sensing Iridium Complexes And Their SiO₂ Hybrid Materials

Phosphorescent iridium complexes have been widely used in the recognition of ions and molecules because of their excellent photophysical and photochemical properties such as high quantum efficiency,long emission lifetime,and feasibly adjustment of emission wavelengths.However,the water solubility for most of iridium complexes is poor,and phosphorescence can be easily quenched by dissolved oxygen in the water.Iridium complexes by using non-toxic and easily available mesoporous silica nanoparticles?MSNs?as inorganic support,and reduced the solvation effect and oxygen quenching effect of phosphorescent emission center by limiting the contact between iridium complexes and external macromolecules as well as solvents.In the paper four new iridium complexes were synthesized and studied.A new type of nanoprobe was prepared by combining the complex of excellent performance with the mesoporous silica nanoparticles.The ion recognition mechanism was also discussed.The main contents and conclusions are summarized as follows:1.Two iridium complexes 1 and 2 were designed and synthesized by using5-aldehyde-2-pyridinethiophene as C^N ligand,and their responses to HSO₃^–were investigated via absorption spectra.The absorption spectra of two iridium complexes are affected by HSO₃^–and show significant changes since HSO₃^–can react with aldehyde groups in an addition reaction way.Unfortunately,there is no phosphorescent response for 1 towards HSO₃^–.With the addition of HSO₃^–,the intensity of the maximum emission peak of 2 at 575 nm gradually increases,changing from no phosphorescence to orange-red phosphorescence.However,the reaction needs a large amount of HSO₃^–,which is not conducive to practical detection applications.2.Iridium complex 3 was synthesized with 5-hydroxy-2-pyridine thiophene as C^N ligand.It is found that 3 do not react with HSO₃^–through absorption spectrum results although 3 has aldehyde group.We designed a new iridium complex 4 by the condensation reaction of 2,3,3-trimethyl-1-?3-sulfonate propyl?-benzo[e]indole with the aldehyde group of 3.HSO₃^–recognition properties of 4 in DMSO/HEPES?pH7.00,1:5,v/v?were investigated.The results of UV-visible absorption spectroscopy show that the addition of HSO₃^–can cause the disappearance of the strong absorption peak at 591 nm,and the color of the solution changes from black to colorless.In addition,the Job's plot and mass spectrometry data indicate that the binding ratio of 4to HSO₃^–is 1:1.It is further confirmed that 1,4-addition reaction occurs between 4and HSO₃-.However,the luminescence of 4 is affected by aqueous solution and the reaction time is long,which makes 4 unfavorable for practical applications.3.Modified with 3-aminopropyltriethoxysilane?APTES?,the mesoporous silica nanoparticles show positive charges on the surface.Transmission electron microscopy?TEM?reveals that the aminated SiO₂ particles disperses uniformly in water and the size is about 150 nm.The nanocomposite material 4/MSNs-NH₂ was successfully prepared by loading 4 with negative charge on the nanoparticles with positive charge.Phosphorescence spectroscopy proves that 4/MSNs-NH₂ can recognize in sequence HSO₃-and Hg²⁺,Cu²⁺in pure water.The addition of HSO₃-can promote the enhancement of phosphorescence,manifesting as orange-red phosphorescence.Its detection limit is as low as 1.3?M.Interestingly,phosphorescence quenching happens with adding more Hg²⁺or Cu²⁺to the solution,and phosphorescence is restored if HSO₃-is added again.Such process can be repeated at least 4 times,which means4/MSNs-NH₂ can recognize HSO₃-and Hg²⁺,Cu²⁺circularly and continuously.