SER(R)S of porphyrins on Ag nanoparticles immobilized by silane:: a unique way to obtain free-base porphyrin spectra

We measured the surf ace-enhanced resonance Raman scattering (SER(R)S) spectra of 5,10,15,20-tetrakis (1-methyl-4-pyridyl)porphyrin (TMPyP) by using solid SERS-active substrates: Ag nanoparticles immobilized by aminosilane on glass plates. We report the surprising result that by using such substrates it is possible to obtain SER(R)S spectra of porphyrins in the unperturbed free-base form, although by using silver nanoparticles directly in solution, the porphyrin molecules are completely metalated. We suggest that silane used for nanoparticle immobilization modifies the surface properties and, therefore, makes porphyrin metalation impossible. Copyright (C) 2007 John Wiley & Sons, Ltd.