Regulation Of Metastable Photoacids On Supramolecular Metallogels Based On Pyridinamide Ligands And Sodium Alginate

Four metastable photoacids,PAH,4-Me O-PAH,5-Me O-PAH and TCFPAH have been synthesized and characterized by¹H NMR,MS and UV-vis spectra.At room temperature,the dark reaction kinetics of photoacid PAH in aqueous solution and Triton X-100 micelles were both a first order reaction with the rate constants（k）1.45×10^-2and 8.00×10^-3s^-1,respectively.The half life(t_1/2)of proton dissociated state SP were 48 and 87 s,respectively.This is good for reaching a higher concentration of proton at the irradiation of visible light and is of great significance for applying photoacid PAH.In aqueous solution and Triton X-100 micelles,PAH with the concentration of 3 m M could provide the minimum p H of 3.6 and 2.6,and the apparent degree of ionization?of PAH were 8.4%and 83.7%,respectively.It is the one unit lower p H that will broaden the scope of the p H sensitive reactions which may be tuned by PAH.To contrstruct visible light responsive metallogels tuned by metastable photoacids,ligands N,N’-bis-4-pyridinyl-isophthalamide（L₁）and N,N’,N’’-tri（pyridin-3-yl）benzene-1,3,5-tricarboxamide（L₂）,were prepared and characterized.Based on L₁and L₂,nine metallogels of Cu（II）,Co（II）or Ag（I）were prepared and the phase diagrams of metallogel were drawn.The metallogels were characterized by IR,SEM and XRD.Some gel samples were subjected to rheological tests.We found that the counter anions play an important role on the stength and minimum gel concentration.Composite hydrogels Ag NO₃-L₁-PAH and Ag BF₄-L₁-4-Me OPAH were prepared and the photo-responsive properties were researched.The color of the Ag NO₃-L₁-PAH gel could be tuned by visible light reversibly.The regulations of p H and concentrations of Ca²⁺in solution of PAH(5.0×10^-4M)and Na₂[Ca（EDTA）](1.0×10^-3M)by visible light were reversible.The concentrations of Ca²⁺in the solution after irradiation were 1.94-3.69 times the concentrations before irradiation.The dynamic frequency scanning of the Ca Cl₂-[Ca（EDTA）]^2--Alg-PAH gel samples were carried out before and after irradiation.From the overall trend,the intensity of the samples after irradiation became stronger than that before irradiation.As the concentration of PAH increases,the ratio of the complex viscosity after irradiation and that before irradiation has a tendency to increase.