Ion/surface reactions at monolayers in solution: A combined surface enhanced Raman-X-ray photoelectron spectroscopic investigation of the chemical modification of a 2-mercaptobenzothiazole monolayer on polycrystalline Au films

Reaction of a methyltriphenylphosphonium (TPP) ion with a 2-mercaptabenzath iazole (MBT) monolayer on polycrystalline gold under electrochemical condit ions leads to the chemical modification of the monolayer. Surface-enhanced Raman spectroscopy (SERS) has been used to study the molecular nature of th e transformation. MET, which adsorbs in the thione form on An, gets transfo rmed to the thiolate form upon reaction. Thermal stability of the modified monolayer is substantially lower than the corresponding pure monolayers and complete desorption of the modified monolayer occurs below 473 K. Time, po tential, and solvent dependence of the reaction has been investigated. Elec tron transfer from the monolayer to the approaching ion in solution is sugg ested as the cause of the reaction. XPS investigation shows the change in t he valence states of the species concerned. While the parent MBT gets oxidi zed, the TPP moiety gets reduced. The results suggest that modified monolay ers can be made by simple electrochemical procedures and the processes are similar to the corresponding gas-phase events (1994, R. G. Cooks, T. Ast, T . Pradeep, and V. H. Wysocki, Acc. Chem. Res. 27, 316). (C) 1999 Academic P ress.