Photoemission and X-Ray Absorption Study of the Interface between 3,4-Ethylenedioxythiophene Related Derivatives and Gold

The chemisorption of 3,4-ethylenedioxythiophene (EDOT) derivatives on Au(111) single crystal and polycrystalline surfacesis studied with valence band photoemission and near edge x-ray absorption (NEXAFS). Different EDOT derived molecules are considered, namely EDOT, its dimer (bi-EDOT), 3’,4’-ethylenedioxy-2,2’:5’,2’’-terthiophene (TET) and the relevant electro-generated polymer, PEDOT, at different stages of substrate coverage. The interpretation of the spectra is carried out comparing with the DFT calculations of the densities of states of different possible reaction products that can be formed at the interface. Simulation of the NEXAFS spectrum of EDOT and comparison with literature work on thiophene and ologothiophene films are used for the interpretation of the X-ray absorption spectra of bi-EDOT and PEDOT as a function of the electro-polymerization time. Valence band features that are associated to EDOT products are identified together with new structures that are ascribed to reactive dissociation products at the interface. In particular the presence of thiophene/oligothiophene molecules is observed, together with possible alkyl chains. NEXAFS indicates that the thiophene rings tend to adopt a planar configuration at the interface.