Electrochemical Characterization of Self‐Assembled Thiol‐Porphyrin Monolayers on Gold Electrodes by SECM

• Published in: Chemphyschem Vol. 7; no. 4; pp. 854 - 862
• Main Authors: Lu, Xiaoquan, Zhang, Limin, Li, Minrui, Wang, Xiaoqiang, Zhang, Yan, Liu, Xiuhui, Zuo, Guofang
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag 10.04.2006; Wiley
• Subjects: Adsorption; Chemistry; Electrochemistry; Electrodes; electron transfer; Electrons; Exact sciences and technology; General and physical chemistry; Gold - chemistry; Membranes, Artificial; Microscopy, Electron, Scanning - methods; monolayers; porphyrin; Porphyrins - chemistry; scanning electrochemical microscopy; self‐assembly; Sensitivity and Specificity; Study of interfaces; Sulfhydryl Compounds - chemistry; Surface Properties; Self assembly; Monolayer; Gold; Thiol; monolayers; Nitrogen heterocycle; Electron transfer; Transition metal; Macrocycle; Characterization; Electrodes; Cyclic voltammetry; self-assembly; Molecular assembly; Porphyrin; Electrochemistry; scanning electrochemical microscopy
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200500492

10.1002/cphc.200500492.absHerein, the scanning electrochemical microscopy (SECM) approach is applied to study the formation of thiol‐porphyrin self‐assembled monolayer (SAMs). Using cyclic voltammetry (CV), the formation process is characterized adopting different probe molecules. The observed phenomena indicate that the formation process is affected by solution properties and the molecular structure of the probe molecules. In K3Fe(CN)6 , the SAMs show a strong electron‐transfer (ET) blocking effect on a pure porphyrin‐modified electrode. However, addition of metal ions to the porphyrin molecules leads to ET. A consistent tendency is observed throughout the modification process using CV and SECM methods. Furthermore, keff values, the apparent heterogeneous rate constants, obtained for different modification periods affirm the validity of these results. SECM images are used to collect surface information in the course of the modification process when the substrate potential is 0.5 V versus Ag/AgCl. The effect of the substrate potential indicates that the oxidation of the porphyrin molecules is supported by more positive potentials because of the similar bimolecular reaction of the porphyrin ring with positive charge and the probe molecules with negative charge. Influencing electron transfer: Thiol‐porphyrin self‐assembled monolayers on gold electrodes, investigated using cyclic voltammetry and scanning electrochemical microscopy (SECM), influence the electron‐transfer process. The substrate potential, the solution properties and the structure of the probe molecules [see figure showing reaction scheme of probe molecule and metalloporphyrin (M)] all play an important role.