title: Photo-induced transformations in 2,2':5',2''-terthiophene thin films on silver.
abstract: We report on transient photo-induced structural changes of 2,2':5',2''-terthiophene (3T) adsorbed on silver nanoparticles. Surface-enhanced Raman scattering (SERS) data show that the film thickness predetermines the eventual course of these changes. In particular, for high molecular concentrations (thick adsorbate layers), illumination leads to a photoinduced polymerization of the 3T film. For thin layers ( approximately monolayer coverage), the photoinduced spectral evolution is qualitatively different. We interpret the latter process as a cleavage of the terthiophene molecule, resulting in isolated thiophene units. Calculations of excitation energies for 3T + 3Ag+ and 1T + Ag+ revealed visible transitions, while calculated Raman frequencies indicated 1T as a possible photoproduct. As no photoinduced transformations are observed for 3T in the solid or solution phases, it is likely that the processes reported here originate in surface-enhanced charge-transfer between the Ag-surface and the organic adsorbate.
authors.affiliation: Department of Applied Physics, Chalmers University of Technology, SE-412 96, Göteborg, Sweden. yury@fy.chalmers.se
authors.forename: Yury
authors.initials: Y
authors.lastname: Alaverdyan
authors.forename: Patrik
authors.initials: P
authors.lastname: Johansson
authors.forename: Mikael
authors.initials: M
authors.lastname: Käll
mesh_terms: D000327:Adsorption; D000890:Anti-Infective Agents / Q000737:chemistry / Q000528:radiation effects; D008027:Light; D008958:Models, Molecular; D012834:Silver; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D013876:Thiophenes / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D000890:Anti-Infective Agents; D013876:Thiophenes; C019101:alpha-terthienyl; D012834:Silver