Study Of The Size And Separation Of Pinholes In The Self-assembled Thiol-porphyrin Monolayers On Gold Electrodes

摘要

Self-assembled monolayers (SAMs) of thiol-porphyrins with different alkyl chain length (abbreviated as H_2TPPO(CH_2)_nSH, n = 3, 6, 9 and 12) on gold electrode have been studied by electrochemical impedance spectroscopy in electrolytes containing a one-electron redox couple. From the size and separation of pinholes on SAMs, both estimated the values of charge-transfer resistance and pore size model, we get the surface coverage (θ). The results demonstrate that the surface coverage of saturated porphyrin modified gold electrode is close to unity (>99%). But on the SAMs, a large number of pinholes still exist and acting as the microelectrodes, with average pinhole radius of 4-6 μm and the separations are ten times greater than the pinhole size, of 40-70 μm. Moreover, long chain length thiol-porphyrin SAM shows high surface coverage, larger pinhole size and excellent blocking of electron-transfer reactions between the redox mediator and the gold substrate. We demonstrated the large pinhole size is due to the aggregation of mass individual "micro-holes".