Chemical and potential-assisted assembly of thiolacetyl-terminated oligo(phenylene ethynylene)s on gold surfaces

Reliable and reproducible methods have been developed for the formation of self-assembled monolayers (SAMs) of thiolacetyl-terminated oligo(phenylene ethynylene)s on a Au surface. The thiolacetyl groups are deprotected in situ and transformed to the free thiol, which then spontaneously forms a SAM. The SAMs are characterized by ellipsometry and electrochemistry, while the solutions are characterized by UV-vis spectroscopy. The results indicate, that the previously described NH4OH/THF mixture is a poor choice for deprotection of thiols bearing multiple nitro substituents. Conversely, use of the more polar system acetone/MeOH/NH4OH or acid conditions CH2Cl2/MeOH/H2SO4 permits the formation of SAMs with thicknesses that are consistent with the predicted length of the molecules. However, the latter acid mixture appears to, be less destructive to the highly electron-deficient multinitro oligomers when analyzed by UV-vis spectroscopy. The potential-assisted assembly is 1-2 orders of magnitude faster than the chemical method. This technique can be directly used to assemble different conjugated oligomers on one electrode to the exclusion of a nearby electrode.