Paper SS2-ThM2
Porphyrin Adsorption on Copper Single Crystal Electrodes Studied by SXPS

Thursday, November 12, 2009, 8:20 am, Room N

Porphyrins are well known as biologically active molecules, e.g. as heme in hemoglobin or chlorophyll in green leaves. Their biological functions originate from their redox activity, which makes their investigation in an electrochemical environment interesting. We have investigated the electrochemically deposited monolayers of Tetra-methylpyridinium-porphyrin (TMPyP)-Tetratosylat on chloride and sulphate precovered Cu(100) and Cu(111) surfaces by means of Cyclic Voltametry (CV), in-situ ElectroChemical Scanning Tunneling Microscopy (EC-STM) as well as ex-situ X-ray Photoelectron Spectroscopy with synchrotron radiation S-XPS at the SoLiAS-station at BESSY II. This station allows the electrochemical preparation of the surfaces and a quick and contaminationfree transfer into UHV. The electrochemical preparation includes the formation of the anion preadsorption in diluted hydochloric- or sulphuric-acid, respectively, and the adsorption and emersion of the porphyrin layer at different potentials within the doublelayer regime.

While the preadsorbed anion layers, i.e. c(2x2) Cl^- on Cu(100), (√3x√3)R30°-Cl^- on Cu(111), quasi- (√3x√7)R30°-SO₄^2- on Cu(111) and a disordered SO₄²-layer on Cu(100), bind the TMPyP-cations electrostatically to the surface variation of the electrode potential causes structural transitions within the selfassembled porphyrin layers, as seen with EC-STM. The S-XPS N(1s) spectra enable a clear correlation of the structural changes with concommitant redox-transition of the TMPyP-cations. As a result structural transitions within the ordered TMPyP-layers are most likely due to different lateral electrostatic interactions between different TMPyP-redox states.