A 2ND-HARMONIC GENERATION ANALOG OF OPTICAL-ROTATORY DISPERSION FOR THE STUDY OF CHIRAL MONOLAYERS

Surface second harmonic generation (SHG) is shown to display optical rotatory effects dependent on the handedness of chiral molecules (2,2'-dihydroxy-1,1'binaphthyl) at various interfaces. The polarization of the surface SHG radiation is rotated with respect to that of the input fundamental radiation in a direction indicative of the chirality of the surface molecules. The origin of SHG-ORD lies in the electric dipole-allowed chi(2) tenser elements, one of which is associated with the handedness of surface species. The SHG-ORD rotation is independent of the density of surface species for an optically pure system, but is dependent on the chiral excess for mixtures of enantiomers. It is wavelength dependent but resonance is not required to observe the rotation. The experiments show that while SHG-ORD has origins quite distinct from ordinary ORD, it can be utilized to measure chiral structures of surfaces.