Effect of CTAB on the Surface-Enhanced Raman Scattering of Tetrakis(4-N-methylpyridyl)porphyrin

Surfactants have significant effects on the properties of liquid-solid surfaces. The effects of surfactants on the surface-enhanced Raman scattering (SERS) of molecules adsorbed on solid substrates have been used to improve the qualities of SERS spectra and to reveal the distance-enhancement relationship of SERS. On the other hand, the adsorption behaviors of porphyrin compounds on surfaces are important for their applications in electrode modification, sensitization of photo-electric transduers and biomimetic catalysis. The effect of cetyltrimethyl ammoniumbromide (CTAB) on the SERS of free-base 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (H2TMPyP) and its Ag-chelate (AgTMPyP) adsorbed on Ag colloid was studied. It was found from the SERS spectra that the adsorbed H2TMPyP molecules undergo silver-incorporation to form AgTMPyP which can change back toH2TMPyPwhen added CTAB. The similar demetallization reaction was aslo observed in AgTMPyP/Ag sol/CTAB systems. The SERS signals were found to be obviously enhanced when added CTAB. The implications of the findings in relation to the change ofmicro-environmenton Ag particles by the addition of CTAB are briefly discussed.