Gold nanoparticles linked by pyrrole-and thiophene-based thiols. Electrochemical, optical, and conductive properties

A series of new alkylsubstituted pyrrole-, bithiophene- and terthiophene-thiols, terthiophene- and sexithiophene-dithiol and polythiophene polythiol have been synthesized. The compounds form self-assembled monolayers on gold with high surface coverages generally in the range 2-4x10-10 mol cm-2 as indicated by cyclic voltammetry and UV-vis spectroscopy. The thiols were reacted with 5-nm gold nanoparticles in toluene to form monodisperse, stable and soluble thiol-capped gold clusters with the same gold core diameter, which were oxidatively coupled electrochemically (in solution or as films) and chemically (with iodine) to polymeric gold clusters. The dithiols (including ethanedithiol) and the polythiol formed analogous polymeric structures via layer-by-layer alternation with gold nanoparticles on gold-modified ITO and glass surfaces. The new materials were investigated by cyclic voltammetry, UV-vis and FTIR spectroscopy and conductivity. The capped gold clusters display conductivities in the range 10-7-10-2 S cm-1 and give solvoconductive responses fast and stable, which parallel the degree of swelling measured by QCM. The conductivity of the polymeric clusters are in the range 2x10-2-10-1 S cm-1. Comparison with the literature indicates 10-1 S cm-1 as a practical limit to the conductivity in such systems.