Studying On The Interface Electron Transfer Behavior Of Porphyrin ModifiedElectrodes

In this paper, we studied the interface electron transfer behavior of porphyrin modified electrodes. Porphyrins as a main body of the research are effectively combined with self-assembled monolayers (SAMs) technique, electron transfer at interfaces as the masterstroke, various electrochemical measurements as the instrument. The electron transfer dynamics of functionalized porphyrins at the modified electrode/liquid interfaces was studied by electrochemical method. Based on this paper, we hope to develop the theory on electron transfer dynamics of porphyrins, and make contribute to the application of porphyrin derivatives in simulation lift system of electron transfer. The major contents are described as follows:Section I we summarized the characteristic of self-assembled monolayers, the progress in application of self-assembled monolayers, the adsorption kinetics of self-assembled, porphyrin self-assembled monolayers in molecular recognition, catalysis, bionics sensor. Considering the degree of correlation with this paper, the characteristic and application of scanning electrochemistry microscope (SECM) in the modified electrode with porphyrins were especially reviewed.Section II By scanning electrochemical microscopy (SECM), the electrochemical behaviors of porphyrins was studied. The synthetic sulfhydryl porphyrin compounds (abbreviated as H2TPPO(CH)nSH, n=3,4,6,9,10,12), with a systematic series of spacers containing large end groups-porphyrin rings and different length alkyl chain, were prepared to investigate the electron transport (ET) kinetics by SECM. As shown by the rate constants (kox) of bimolecular ET between H2TPPO(CH)nSH and the redox mediator, the rate constants (kb) of tunneling ET between the underlying gold electrode and the redox mediator and the rate constants (k1) of pinhole or defects, that indicated ET depended upon alkyl chain length, surface coverage and the concentration of the redox mediator. Among all of them, the bimolecular reaction which contained electron donor (mediators) and electron accepter (SAMs) was a dynamic cyclic process. That strongly suggested that the bimolecular reaction should mimic ET of photosystem â…¡ in chloroplast.Section â…¢ The ITO electrode modified with porphyrins was used to study photoinduced ET. The dynamics of photoinduced heterogeneous electron transfer (ET) between sulfhydryl porphyrin compounds (abbreviated as H2TPPO(CH2)12SH) and electron mediator (ferricyanide) was investigated by scanning electrochemical microscopy (SECM). The basic features of the photoinduced electron were record by feedback approach curve within the framework of the bimolecular ET mechanisms. The potential dependence of the feedback current curves at various light source wavelength and intensity provided a2-dimensional quantitative analysis on photoinduced heterogeneous ET at ITO/liquid interface. The change of heterogeneous rate constant (Keff) was of the same order as the light source intensity. These results provide valuable information for artificial photosynthetic system on porphyrin molecular at ITO substrate.Section IV The electrochemical behaviors of self-assembled substituted porphyrins (SH-terminated, abbreviated as H2TPPO(CH2)nSH, n=3,12) on a gold electrode were investigated using the steady-state scanning electrochemical microscopy (SECM). The different electron-transfer (ET) kinetics, including the bimolecular ET between the porphyrin self-assembled monolayers (SAMs) and the redox mediator [K3Fe(CN)6], the tunneling ET between the underlying gold electrode and [K3Fe(CN)6], and pinholes or defects, were clearly distinguishable. The SECM strategy was developed to deal with the two types of porphyrin SAMs. First, a model using alkanethiols [(CH2)nSH, n=3,12] as the functional template was proposed to change the conformation of porphyrin SAMs in a unit area of the electrode. Second, the porphyrin SAMs were directly prepared by inserting a metal (cobalt) into the center of the porphyrin ring. The results show the distinct effect of the presence of alkanethiols on the kinetics of the different-chain length porphyrins. In addition, the rate constants of the bimolecular ET significantly increased after the insertion of cobalt. The results are in agreement with the density functional theory (DFT).