KINETICS OF DISPLACEMENT AND CHARGE-TRANSFER REACTIONS PROBED BY SERS - EVIDENCE FOR DISTINCT DONOR AND ACCEPTOR SITES ON COLLOIDAL GOLD SURFACES

Both the electron donor tetrathiafulvalene (TTF) and the electron acceptor tetracyanoquinodimethane give large surface enhanced Raman scattering (SERS) signals upon adsorption onto colloidal gold particles, but only TTF displaces previously adsorbed pyridine, indicating that molecular donors and acceptors occupy different surface sites. The acceptor (Lewis acid) site probably involves a reducible metal complex of Au** plus while the donor (Lewis base) site may be associated with Au**0. The kinetics for the charge-transfer reaction involving two distinct TTF oxidation states can be explained by migration of the adsorbate from the donor to the acceptor site.