Self-assembled monolayers of 4-mercaptobiphenyls.

This Account focuses on our systematic studies of the formation and properties of self-assembled monolayers (SAMs) of 4-mercaptobiphenyls on gold surfaces. The key difference between alkanethiolate and biphenyl thiolate SAMs 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 molecular dipole moment that affects the adsorption kinetics as well as the equilibrium structure of mixed SAMs. Due to the lack of conformational disorder in the assembling molecules, these SAMs can serve as stable molecularly engineered model surfaces. Infrared spectroscopy and scanning tunneling microscopy, as well as X-ray and helium diffraction studies, suggest that biphenyl moieties in the SAMs have small tilt angles with respect to the surfaces normal. Finally, the morphology of glycine crystals nucleated and grown on these SAM surfaces depends on the structure of the nucleating glycine layer, which, in turn, depends on the H-bonding of these molecules with the SAM surface.