Study On Electrochemistry And Spectroelectrochemistry Of Hexaphyrins

Porphyrins are conjugated macrocyclic compounds which contain four methane bridges between the four pyrrolic subunits.They have a great potential application in the field of medical and material chemistry.Hexaphyrins are one of the expanded macrocyclic compounds which consist of six pyrrole subunits.Because hexaphyrins have unique spectral and electrochemical properties,to study these compounds may have important academic significance and potential application values.The first Chapter of this thesis summarized the structural properties of porphyrins and expanded porphyrins,their application in medicine and materials and the main research methods.The second Chapter studied the electrochemistry of the free-base porphyrins in different solvents and discuss the effect of solvents on the redox reactions.All the reductions and oxidations of each compound in the certain solvent are one-electron transfer processes occurring on the porphyrin macrocycle.The products of the first reduction and first oxidation are porphyrin anion radical and porphyrin cation radical,respectively.In addition,protonation reaction of HexaPyH₂ was also examined in dichloromethane.Neutral HexaPyH₂ can accept two protons in one-step when reacts with TFA to generate [HexaPyH₄]²⁺.In the third Chapter,electrochemical and spectroelectrochemical properties of T2,6-diFPPCu,T2,6-diFPPZn and HexaPyCu₂,HexaPyZn₂ were examined in nonaqueous media.The results showed that T2,6-diFPPCu,T2,6-diFPPZn undergo two one-electron reductions in the given solvents to generate mono-anions and bis-anions,i.e.[T2,6-diFPPM]-and [T2,6-diFPPM]^2-.However,HexaPyCu₂ and HexaPyZn₂ undergo four reversible one-electron reductions to give [HexaPyM₂]^-,[HexaPyM₂]^2-,[HexaPyM₂]^3-and [HexaPyM₂]^4-,respectively under the same solution conditions.In the fourth Chapter,the electrochemical and spectroelectrochemical properties of T2,6-diFPPCo and HexaPyCo₂ were investigated in nonaqueous media.The first reduction and first oxidation of T2,6-diFPPCo are metal-centered electron transfer processes in DCM or PhCN,and the corresponding products of the reduction and oxidation are Co???porphyrin and Co???porphyrin,respectively.HexaPyCo₂ contains two cobalt???central ions,it undergoes three one-electron reductions in the same solvent with the first and second reductions occurring on each of the two Co???central ions to generate [HexaPyCo???₂]^2-.The first two oxidations of the hexaphyrin are also metal-centered electron transfer processes to stepwise oxidized the two Co???ions and generate [HexaPyCo???₂]²⁺ as the final products.Each of the Co???in HexaPyCo₂ can axial bind with a pyridine to generated [HexaPyCo₂?py?2].This five-coordinate compound undergoes three reductions in pyridine.The first reduction is a two overlapping one-electron reduction to form the Co???hexaphyrin.Axial binding reaction of T2,6-diFPPCo,HexaPyCo₂ with Im,MeIm,Py and picoline was also studied in CHCl₃.The reaction equilibrium constants were calculated using standard method.In addition,the catalytic properties of HexaPyCo₂ for oxygen reduction reaction?ORR?in aqueous solution were examined by using rotating disk electrode.The results indicated that HexaPyCo₂ can be used as an electrocatalyst for ORR in 1.0 M HClO₄.The ORR is a two-electron process and the product is mainly hydrogen peroxide.