Self-assembled monolayers of 4-mercaptobiphenyls

This Account focuses on our systematic studies of the formation and propert ies of self-assembled monolayers (SAMs) of 4-mercap-tobiphenyls on gold sur faces. The key difference between alkane-thiolate and biphenyl thiolate SAM s is the rigid pi -character of the latter. The pi -conjugation between the adsorbing thiolate and the substituent at the 4'-position results in a mol ecular dipole moment that affects the adsorption kinetics as well as the eq uilibrium structure of mixed SAMs. Due to the lack of conformational disord er in the assembling molecules, these SAMs can serve as stable molecularly engineered model surfaces. Infrared spectroscopy and scanning tunneling mic roscopy, as well as X-ray and helium diffraction studies, suggest that biph enyl moieties in the SAMs have small tilt angles with respect to the surfac es normal. Finally, the morphology of glycine crystals nucleated and grown on these SAM surfaces depends on the structure of the nucleating glycine la yer, which, in turn, depends on the H-bonding of these molecules with the S AM surface.