Formation of self-assembled monolayer of curcuminoid molecules on gold surfaces

Abstract We investigated the formation of self-assembled monolayers of two thiophene curcuminoid molecules, 2-thphCCM ( 1 ) and 3-thphCCM ( 2 ), on polycrystalline gold substrates prepared by immersion of the surfaces in a solution of the molecules during 24 h. The functionalized surfaces were studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Despite the fact that both molecules have the same composition and almost the same structure, these molecules exhibit different behavior on the gold surface, which can be explained by the different positions of the sulfur atoms in the terminal aromatic rings. In the case of molecule 1 , the complete formation of a SAM can be observed after 24 h of immersion. In the case of molecule 2 , the transition from flat-lying to upright configuration on the surface is still in process after 24 h of immersion. This is attributed to the fact that molecule 2 have the sulfur atoms more exposed than molecule 1.