Evidence of electron-transfer in the SERS spectra of a single iron-protoporphyrin IX molecule

Surface enhanced Raman spectroscopy is applied to study single molecule iron-protoporphyrin IX, adsorbed on silver colloidal surfaces. If on one hand, drastic, random intensity and frequency fluctuations are observed in the Raman lines, on the other, a time dependent switching between Fe3+ and Fe2+ states is evidenced. Such a charge transfer, due to ballistic electrons oscillating across the molecule and the metal surface, could provide some insight on both the surface enhanced Raman mechanisms and the interfacial electron transfer in hybrid systems.