Formation and Analysis of Self-Assembled Monolayers from U-Shaped Oligo(phenylene ethynylene)s as Candidates for Molecular Electronics

We present the synthesis of novel oligo(phenylene ethynylene)-[1,1ʹ;3ʹ1ʹ ʹ]terphenyls and oligo (phenylene ethynylene)-1,8-anthracenes and their analyses at the metal-molecule interface when forming self-assembled monolayers (SAMs) on gold surfaces. The target compounds were synthesized with thioacetate functionalities that serve as molecular "alligator clips" upon thiol deprotection, to promote metallic adhesion. The resulting monolayers were studied, and the integrity of the molecule-gold attachment was corroborated by single-wavelength ellipsometry (SWE), cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS). Additionally, the kinetics of SAM formation on a gold electrode were probed by CV, while a clear signal corresponding to the thiol-gold bond was detected by XPS. These conformationally restricted oligomers are designed to be of use in studies utilizing scanning probe microscopy techniques to elucidate switching mechanisms and negative differential resistance behavior thought to be based on molecular conformational changes.