Molecular orientation distribution, second harmonic generation

Microscopy methods based on nonlinear optical phenomena that provide chemical information are a recent development. Infrared snm-frequency microscopy has been demonstrated for LB films of arachidic acid, allowing for surface-specific imaging of the lateral distribution of a selected vibrational mode, the asymmetric methyl stretch [60]. The method is sensitive to the snrface distribntion of the functional gronp as well as to lateral variations in the gronp environmental and conformation. Second-harmonic generation (SHG) microscopy has also been demonstrated for both spread monolayers and LB films of dye molecules [61,62]. The method images the molecular density and orientation field with optical resolution, and local qnantitative information can be extracted. 

Second harmonic generation is a useful tool in probing the molecular behaviour at the liquid/liquid interface. While its limitations must be taken into account, particularly over the contributions of the observed signals from the bulk phases and the interrelated contributions of molecular density and orientation distribution, the ability to differentiate molecules at the interface from the bulk, is extremely useful. While the related... 

Y. Rao, S. Y. Hong, N. J. Turro, and K. B. Eisenthal,/. Rhys. Chem. C, 115, 11678 (2011). Molecular Orientational Distribution at Interfaces Using Second Harmonic Generation. 

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