CHROMOPHORE STRUCTURE, 2ND-HARMONIC GENERATION, AND ORIENTATIONAL ORDER IN ZIRCONIUM PHOSPHONATE/PHOSPHATE SELF-ASSEMBLED MULTILAYERS

Two new phosphonate-terminated polar azo dyes, one that is substantially rigid (1) and the other with a large molecular hyperpolarizability (2), were designed and incorporated into zirconium-based surface multilayers. Second harmonic generation (SHG) was observed from the multilayers as a function of incident and polarization angles and compared with that from the previously reported aminophenylazophenylphosphonic acid chromophore 3. The new dyes are analogous to moieties commonly used in electric field-poled polymers, allowing comparisons between the polymers and the multilayers. Apparent order parameters (cos(3) theta) are >0.2 for 1 and approximate to 0.16 for 2. Because of local field effects, the value for 1 is probably a lower limit. Use of other dyes that are both rigid and highly polar led to H-aggregation. Insertion of a nonpolar chromophore layer among the polar layers had no effect on SHG. The syntheses involved several novel reactions, involving the preparation of an unsymmetrically substituted diphenylpiperazine, an anilinoalkyl phosphonate, and the deprotected phosphonic acids themselves.