Molecule orientation in self-assembled monolayers determined by infrared-visible sum-frequency generation spectroscopy

The molecular orientation in self-assembled monolayers of thiophenol (TP) on Ag(1 1 1) and of para-nitroanilinododecane- thiol (NAT) on Au was investigated by infrared-visible sum-frequency generation between 500 and 1500 cm 1. Ab initio calculations were performed to determine the interface nonlinear response. The combined experimental and theoretical results reveal that the S–C bond of TP is tilted 37 from the Ag(1 1 1) surface normal, with the aromatic ring plane perpendicular to the surface. On Au, the tilt angle of the NAT molecule stabilizes below 60 at the end of film growth.