Electrochemistry of metal porphyrin monolayers adsorbed on gold single crystal surfaces

The main objective of this work is the investigation of the electrochemical activity of metal porphyrines as monolayers adsorbed on gold single crystal surfaces. That aim was successfully fulfilled. The formation of monolayers of cobalt (II) phthalocyanine (CoPc) adsorbed on Au (111) electrodes was probed by the in situ electrochemical scanning tunneling microscopy (in situ EC-STM) approach. This technique was also employed to track the electrochemical reduction of 02 at the CoPc modified surfaces. Changes in the STM features of the adsorbed molecules were observed under oxygen, which were attributed to structural as well as electronic transformations in the interacting species. The obtained results were correlated to the electronic structure of the phthalocyanine intermediates by means of density functional theory (DFT) calculations.;Electrochemical properties of metal porphyrazine adsorbates were elucidated in this thesis. Octamethylthio magnesium and octapropyl magnesium porphyrazines along with their metal free counterparts were investigated and the reported electrochemical characteristics were attributed to the porphyrazines ring oxidation-reduction activity. In addition, magnesium octamethylthio porphyrazine monolayers were detected by the in situ STM technique and molecular properties of the four studied porphyrazines were analyzed using DFT.;Effect of addition of imidazole to the phthalocyanines modified and bare gold surfaces on the reduction of oxygen was also studied. The reduction reaction was investigated with imidazole co-adsorbed with CoPc, with imidazole axially binding to the adsorbed phthalocyanines, and with imidazole adsorbed on bare Au (111) surfaces. Formation of monolayers of imidazole and CoPc adsorbed on Au (111) surfaces was confirmed by the STM method. The CoPc modified surface demonstrated the highest activity toward the reduction reaction. The reported activity was reduced by imidazole co-adsorption. On the other hand, the surface modified with imidazole axially binding to CoPc was found to be the least active electrode amongst the studied systems, mainly because of blocking of the Co (II) centers by the binding imidazole molecules. Surprisingly, the imidazole modified Au (111) exhibited a higher activity toward O2 reduction than its bare counterpart, which was attributed to modification of the electronic nature of the gold surface atoms by the adsorbed imidazole molecules.