Studies of Orientational Order in Monolayers of Nonlinear Optical Dye Molecules.

We present results of studies of orientational order of Langmuir- Blodgett monolayer and multilayer films based on second harmonic generation and linear absorption measurements. Two new compounds, a tricyanovinyl aniline and a tricyanovinyl azo dye, both possessing large second order molecular susceptibilities, have been synthesized and transferred as monolayers from the air-water interface to solid substrates using the Langmuir-Blodgett technique. Both of these compounds, although non-ionic, form monolayers which can be transferred to a substrate. However, the azo dye is a superior Langmuir-Blodgett material. The azo dye has an area/molecule on the water surface which agrees with molecular modeling, and once transferred to a substrate, forms a film with stable chemistry and orientational order. Multilayers of azo dye show an enhancement in polar orientational order with thickness, as observed in the dependence of the second harmonic polarization components on number of layers.