Surface-enhanced fluorescence and surface-enhanced Raman scattering of push-pull molecules: sulfur-functionalized 4-amino, 7-nitro-benzofurazan adsorbed on Ag and Au nanostructured substrates

We investigated the chemisorption of selfassembled monolayers of sulfur-functionalized 4-amino-7-nitrobenzofurazan on gold and silver nanoisland films (NIFs) bymeans of surface-enhanced fluorescence (SEF) and surface enhanced Raman scattering (SERS). The ligand is a push–pull molecule, where an intramolecular charge transfer occurs between an electron-donor and an electron-acceptor group, thus exhibiting nonlinear optical properties that are related to both SERS and SEF effects. The presence of different heteroatoms in the molecule ensures the possibility of chemica interaction with both silver and gold substrates. The SERS spectra suggest that furazan is bound to silver via lone pairs of the nitrogen atoms, whereas the ligand is linked to gold via a sulfur atom. Silver NIFs provide more efficient enhancement of both fluorescence and Raman scattering in comparison with gold NIFs. The present SEF and SERS investigation could provide useful information for foreseeing changes in the nonlinear responses of this push–pull molecule.