EVIDENCE FOR A PHOTON-DRIVEN CHARGE-TRANSFER ENHANCEMENT IN THE SURFACE-ENHANCED RAMAN-SCATTERING OF 1,4-DIAZABICYCLO[2.2.2]OCTANE AT A SILVER ELECTRODE

The surface-enhanced Raman (SER) spectra of the aliphatic amine l,4-diazabicyclo[2.2.2]octane (DABCO) adsorbed on the surface of silver electrodes have been studied in detail as a function of the electrode potential and the excitation energy. Variations in the SERS intensity resulting from the variation in these two parameters and the supporting electrolyte have been characterized and attributed to the existence of a photon-driven charge-transfer (PDCT) enhancement of 1-2 orders of magnitude, of the adsorbed DABCO molecule, which operates in addition to an electromagnetic enhancement. The direction of the charge transfer is from molecule to metal. Variations in the band frequencies of the adsorbed DABCO with electrode potential and with the supporting electrolyte have also been measured and ascribed to the existence of a ground-state charge transfer between adsorbed DABCO and the silver electrode. The Raman spectrum of a charge-transfer complex between DABCO and iodine is presented for comparison. © 1990, American Chemical Society. All rights reserved.