Novel 3,4-Disubstituted Thiophenes for Weak Passivation of Au Nanoparticles

Novel self-assembled monolayers of 3,4-disubstituted thiophenes (3,4-dioctylthiophene and 3,4-diheptyloxythiophene) were prepared and characterized by contact angle measurements, ellipsometry and X-ray photoelectron spectroscopy. In addition, Au nanoparticles passivated with the 3,4-disubstituted thiophenes (3,4-dioctylthiophene and 3,4-diheptyloxythiophene) and monosubstituted thiophene (3-octylthiophene) were synthesized and characterized by UV/visible spectroscopy, transmission electron microscopy and dynamic light scattering. The Au nanoparticles had diameters in the range 5-7 nm. The Au nanoparticles stabilized with the thiophene derivatives were, as expected, less stable than the Au nanoparticles passivated with decanethiol and didecylsulfide. Surprisingly, the particles passivated with the monosubstituted 3-octylthiophene were more stable than the 3,4-dioctyl and 3,4-diheptyloxythiophene passivated particles. Such lower stability Au nanoparticles may find uses as negative tone resists in the formation of nanowires by e-beam lithography, via the more readily cleavable Au-S bond.