Modification of gold nanoparticle surfaces with pyrenedisulfide in ligand-protected exchange reactions

We provide a study of ligand place-exchange reaction on Au nanoparticles. Nanoparticles of the dimensions of 7-9 nm were fabricated by high-temperature anhydrous route in the presence of primary aliphatic amine. The advantage of weak coordination to gold, through the nonbonding electrons of the amino group, was to use in an exchange of an initial protective ligand. Therefore, among other stabilizing agents, photoactive dialkyldisulfide molecules functionalized with fluorescent pyrene moieties were attached. The photophysical properties of such a stabilized gold system were investigated during place-exchange reaction. Fluorescence studies show that the excimeric band, characteristic of bispyrene, disappears in the spectrum after binding to the gold NPs, indicating that pyrene molecules are adsorbed separately on the surface. Efficient quenching of monomeric emission suggests that deactivation of the fluorescent excited state occurs through a radiationless transition, probably a charge transfer one, formed due to prior electron transfer from pyrene moiety to gold. Kinetics of chemisorption of pyrene disulfide and its desorption in the presence of thiols was also studied, revealing that both processes comprise a fast and a slow component with an overall rate higher for the desorption.