Hydrogen Bonding: A Bottom-Up Approach for the Synthesis of Films Composed of Gold Nanoparticles

Citrate gold nanoparticles of 13.5 nm average diameters have been synthesized by Turkevich method and further functionalized by place exchange reaction using mercaptosuccinic acid (MSA), 1,4-benezenedimethanethiol (1,4BDMT) or mercaptoundecanoic acid (MUA) as the incoming ligands. In the first case, the functionalization of the gold clusters with MSA yielded solution of blue color and large aggregates on carbon grids. Moreover, after filtration and drying, any film formed by hydrogen bonding, could not be removed from the filter, being embedded into the filter texture. The second ligand used for the place exchange reaction, the 1,4BDMT, determined the change of the solution color from red to dark purple, and generation of a purple powder but no film formation. In the third case, the purification and drying of the MUA functionalized gold clusters yielded films of purple color with homogenous composition, robustness, soft topographies and remarkable optical properties which were dependent on their thicknesses. The Au-MUA NP films obtained are new, being generated by hydrogen bonding and having features which makes them very attractive for the fabrication of optoelectronic devices. The long alkyl chained thiol proved to be the adequate ligand for film synthesis.