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

Abstract

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.

Surface-Enhanced Raman Scattering of Rhodamine 123 in Silver Hydrosols and in Langmuir–Blodgett Films on Silver Islands

“…[1] and [2] for colloidal SERS and Eq. [3] for LB-SERS. In both cases, 514-nm laser excitation was used for SERS and 609 nm for NRS.…”

“…One is due to the pronounced perturbation with some rough metal surfaces that can cause large enhancement of the incident and scattered electromagnetic fields (2). The second contribution is due to the increase in the scattering cross section of adsorbed molecules in comparison with its free counterpart due to a photon-driven charge transfer (CT) process that involves dynamic charge transfer between the elec-tronic states of the molecule and the metal (3,4). An area of contemporary interest in SERS study is to specify the contribution of the charge transfer mechanism to the overall SERS enhancement.…”

SERS detection of indirect viral DNA capture using colloidal gold and methylene blue as a Raman label

“…CE is attributed to the charge-transfer interactions of a chemiadsorbed scatterer on a metal surface (i.e. SERS substrate) (Guzonas et al, 1990) and EM to the spatial positioning of a physiadsorbed scatterer within an enhanced electromagnetic field arising from light excitation of surface metal electron oscillations, or plasmon resonance (Zeman and Schatz, 1987). The highest levels of SERS enhancement have been reported for EM "hot spots", which are defined as the interstitial, or fractal space, junctions between two or more SERS substrates (Michaels et al, 2007).…”

Anion-induced charge-transfer enhancement in SERS and SERRS spectra of Rhodamine 6G on a silver electrode: how important is it?

“…Such an increase is usually explained in terms of a photon-driven charge transfer (PDCT, shortened to CT) process which involves dynamic charge transfer between electronic states of the molecule and the metal. 3,4 The most straightforward evidence that CT contributes to surface-enhanced Raman scattering (SERS) at the electrode surface is the shift of the potential at which the maximum intensity is observed with (E max ) the photon energy of the incident light.3,4 There are two kinds of experiments which can be performed in order to estimate the relative CT contribution to the SERS on metal electrodes. 5 In the Ðrst, the inÑuence of the CT e †ect on SERS intensity is estimated from the excitation proÐles measured at various constant electrode potentials and then analysed together in order to eliminate the wavenumber-dependent electromagnetic e †ect.…”