Solvent Refractive Index and Core Charge Influences on the Surface Plasmon Absorbance of Alkanethiolate Monolayer-Protected Gold Clusters

Abstract

This report describes the effect of solvent refractive index and core charge on the surface plasmon absorbance of alkanethiolate monolayer-protected gold clusters (MPCs). Solution spectra of dodecanethiolate MPCs (5.2 nm average diameter) reveal an 8-nm shift in plasmon band position as the solvent refractive index is varied from nd20 = 1.33 to 1.55. The spectral shift agrees with predictions of Mie theory when the alkanethiolate monolayer is accounted for in the calculations. Electronic charging of the MPC gold core by electrolysis, from its rest potential (-0.16 V) to +0.82 V vs a Ag quasi-reference electrode, causes a 9-nm (516 to 525 nm) shift in the surface plasmon band position. The sh..