Synthesis And Study On Electrochemical Properties And Mechanism Of Novel Porphyrin Related Derivatives

Porphyrins and porphyrin related derivatives with larger conjugated ? system have specific biology activity and play an important role in oxygen transport, storage, activation and electron transfer in the body of life. Corroles having similar structures as porphyrins are also porphyrin related derivatives. Porphyrins and porphyrin-like have been widely used in different fields such as life sciences, environment and energy, electronic sciences, analytical chemistry and material sciences.Spectroscopic and electrochemical properties of porphyrin related derivatives can be tuned by changing the type and number of peripheral substituents on the meso- or ?-positions of porphyrin macrocycle or by changing the site of central nitrogen atoms(such as inverting one or two pyrrole groups) to modify the electron density or structure of the molecule. Usually, there are two NH- groups in a porphyrin inner macrocycle which can lose the two protons to form a porphyrin dianion. The formed dianion can coordinate with different metal ions to form metalloporphyrins having specific properties in photochemistry, electrochemistry, photophysics and photobiology. These metalloporpyrins with specific properties have wide potential applications in anti-canter medicine, catalysts, molecule and electron devises and other materials.In this dissertation, several types of porphyrin related compounds(include porphyrins and corroles) were synthesized and characterized and the basic structure, chemical and physical properties of these compounds were examined. The redox properties as well as electron transfer mechanisms were investigated by electrochemistry and spectroelectrochemistry. Influence in changing substituents and inner macrocycle structure on compound spectra and electrochemistry properties were also discussed.As shown in the previous studies, porphyrin and porphyrin related compounds are multiple functional materials which have potential applications in fields as catalysts for reduce organic contaminates in environment or catalytic materials for electrodes in advanced fuel cell. In this dissertation, rotating-disk and rotating-ring-disk electrode techniques are used to investigate the catalytic activity of the Fe, Co or Mn metalloporphyrins or metallocorroles for oxygen reduction. The relation ships between the structures and catalytic properties were also discussed.The main results of this dissertation are summarized below.1. Four nitrated NO2-substituted N-confused free-base tetraarylporphyrins with different substituents on meso-positons were synthesized and characterized by electrochemistry and spectroelectrochemistry in nonaqueous media. Unlike the existing of two different froms of the non-NO2 N-confused porphyrins in different solvents, the same form is observed for the NO2 substituted derivatives in different solvents. Density functional theory(DFT) and time-dependent density functional theory(TD-DFT) calculations simulated the UV-vis spectra and gave the molecular orbital energy of the investigated compounds. As shown by the electrochemistry result, neither the first reduction or first oxidation products are stable and can be deprotonated during reduction or protonated during oxidation. As compared to the non-NO2 N-confused derivatives, the nitrogroup itself on the inverted pyrrole is not reduced under the given experiment conditions, but its presence significantly affects both the UV-vis spectra and redox potentials.In addition, four NH2-substituted N-confused free-base tetraarylporphyrins were synthesized by reduction of the corresponding NO2-substituted derivatives and then characterized by UV-vis spectra, NMR and mass spectroscopy. As indicated by the experiment results, only one form is observed for the amino substituted derivatives in different solvents. The DFT and TD-DFT calculation were used to simulate the neutral UV-vis spectra and calculate the molecular orbital energy.2. Several types of copper tetraarylporphyrins containing ???’-fused tetrabutano or tetrabenzo groups were synthesized and characterized. Electrochemistry and spectroelectrochemistry properties as well as the electron transfer mechanisms of the butanoporphyrin and benzoporphyrin were studied in nonaqueous media. Each neutral porphyrin in the two series is ESR active, indicating that the oxidation state of copper is +2 in both series of the derivatives. Each Cu(II) porphyrin also undergoes two reversible one-electron reductions and two reversible one-electron oxidations in nonaqueous media to give a ?-anion radical and dianion upon reduction and a ?-cation radical and dication upon oxidation.The reversible half-wave potentials for the first oxidation of each compound in both series is shifted negatively by about 500 mV as compared to E1/2 values for oxidation of the related copper tetraarylporphyrins without the fused rings while smaller positive shifts of 60 and 300 mV are seen for reduction of the tetrabenzotetraarylporphyrins and tetrabutaotetraarylporphyrins, respectively, as compared to the same redox reactions of the related tetraarylporphyrins. The electrochemically measured HOMO-LUMO gap averages 2.33±0.03 for(TpR-PP)Cu, but only 2.04±0.06 V for butano-(TpR-PP)Cu and 1.76±0.05 V for benzo-(TpR-PP)Cu.3. Several cobalt tetraarylporphyrins containing ???’-fused tetrabutano or tetrabenzo groups were synthesized. Electrochemistry and spectroelectrochemistry properties as well as the electron transfer mechanism of the butanoporphyrins and benzoporphyrins were examined in nonaqueous media. Each Co(II) porphyrin undergoes three reversible one-electron oxidations and one or two reductions in CH2Cl2 and PhCN containing 0.1 mol.L-1 tetra-n-butylammonium perchlorate(TBAP) as supporting electrolyte. Both of the first oxidation and reduction process are cobalt centered electron transfer process to from Co(III) or Co(I), respectively. The other oxidations at more positive potentials or reductions at more negative potentials are all porphyrin ring centered electron transfer processes.In addition, the new synthesized cobalt derivatives were also used as catalysts for oxygen reduction. In 1.0 mol.L-1 HClO4, tetrabutanocobaltporphyrsn can reduce oxygen by two electrons(n = 2.0) to form hydrogen peroxide while tetrabenzocobaltporphyrins can reduce oxygen to give a mixture of hydrogen peroxide and water with the number of electrons transferred n = 2.4-3.1 in the same solution conditions. This indicated that the ???’-fused tetrabutano or tetrabenzo groups have significant effect on the catalytic properties of cobalt porphyrins. The ???’-fused tetrabutano fused derivatives can be used as selective catalysts for oxygen reduction by two-electron transfer process under the given experiment conditions.4. Copper triarylcorroles containing a ?-pyrrole nitro substituent and different meso-position substituents were synthesized and characterized. UV-vis spectrum in different solvents are consistent with an initial assignment of CuII-Cor?2-. All of the ?-nitro copper corroles have three one-electron reductions and the first two of which are reversible. As compared the electrochemical and spectroelectrochemical behavior to the non-NO2 copper corrole, the ?-nitro copper corroles have different site of electron transfer during the second reduction. It is proved in the first time that the second reduction of non-NO2 copper corrole located on corrole macrocycle to form [CuIICor]2-, while the second electron transfer of ?-nitro corrole located on copper center with a Cu(II)/Cu(I) process to form the product with an unreduced macrocycle which is represented as [CuICor]2-. In addition, The DFT and TD-DFT calculation were used to simulate the neutral UV-vis spectra and calculate the molecular orbital energy.5. Two meso-dichlorophenyl substituted Fe and Mn centered corroles were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in dichloromethane, pyridine and other nonaqueous media. The catalytic activity for the electoreduction of dioxygen was also investigated. The main O2 reduction reaction is a two electrons transferred process instead of four electrons to form hydrogen peroxide under the given experimental conditions. As indicated by the experiment result, both of the iron and manganese corrole can be used as catalysts for oxygen reduction reaction. But the catalytic efficient is lower since the dichlorophenyl groups on porphyrin meso-positons have steric hindrance which may prevent the molecule dimerization on the surface of electrode.