Polar orientation of a pendant anionic chromophore in thick layer-by-layer self-assembled polymeric films

Multilayer films with up to 600 bilayers and 740 nm thickness were fabricated using the alternating deposition of poly(allylamine hydrochloride) and poly{1-[p-(3′-carboxy-4′- hydroxyphenylazo)benzenesulfonamido]-1,2-ethandiyl} on glass substrates. Linear relationships for absorbance, thickness, and the square root of the second harmonic intensity versus the number of bilayers demonstrates that the films have long range polar order and optical homogeneity. The deposition conditions (i.e., pH of the solutions, solvent quality, deposition and rinsing times) are critical variables in fabricating layer-by-layer thick films that exhibit long range polar orientation of chromophores. The ability to fabricate noncentrosymmetric films on the order of a micron thick with bulk second order nonlinear optical responses is crucial because it enables the development of nonlinear optical waveguide devices such as electro-optic modulators.