Water soluble azo polymers for electronic and photonic applications

The focus of this dissertation is the design and synthesis of novel water soluble azo polymers and their processing into molecular level multilayer films with unique electronic and optical phenomena. Conjugated main chain azo polymers are expected to exhibit interesting electrical and optical properties. Through an oxidative coupling reaction of 2,5-diaminobenzene sulfonic acid, a high molecular weight, conjugated, main chain azo polymer was synthesized. The polymer was soluble in water and organic solvents such as DMF and DMSO. Two classes of water soluble side chain azo polymers, one epoxy based and the other acrylic acid based, were also synthesized. The polymers were designed to contain ionizable groups in the azo chromophore. All these polymers can be processed in a manner similar to the conventional azo polymers. In addition, the water solubility of the polymers has been utilized in fabricating multilayer films through a recently reported layer-by-layer deposition process. Using the water soluble azo polymers in the ionized form and commercially available oppositely charged polyelectrolytes, multilayers were formed through an alternate deposition process. The azo chromophores in the multilayer films containing the epoxy based azo polymers self-assemble into an acentric arrangement during the deposition process. The films exhibit second order nonlinear optical (NLO) coefficients comparable to the poled, spin coated films of the same polymer. This result indicates that the chromophores in the multilayer films possess the same order of noncentrosymmetric alignment as in the case of the poled films. The self-organization of the chromophores in the multilayer films was confirmed using transmission electron microscopic (TEM) studies. Electron diffraction pattern from the films indicate that the chromophores assemble into a liquid crystal type of order with a d spacing of about 4.7 A. Additional evidence of orientational order was obtained from electroabsorption spectroscopy which is a useful technique in determining the nonlinear optical coefficients {dollar}chisp{lcub}(3){rcub}{dollar}1133 and {dollar}chisp{lcub}(3){rcub}{dollar}3333 of NLO films. The ratio {dollar}chisp{lcub}(3){rcub}{dollar}3333/{dollar}chisp{lcub}(3){rcub}{dollar}1133 is an indication of the orientational order of the relevant chromophore. If the ratio is {dollar}<{dollar}3, it indicates that the chromophores lie preferentially in the plane of the film. If the ratio is =3, the film is isotropic. If the ratio is {dollar}>{dollar}3, the chromophores are predominantly oriented normal to the plane of the film. The electroabsorption results indicate that in the multilayer films the ratio is about 4, whereas in the spin coated film it is about 1.9. These results collectively indicate that we have achieved acentric ordering of azo NLO chromophores through a simple layer-by-layer deposition process. (Abstract shortened by UMI.)...