Enhancement and investigation of second-order nonlinearity through rational design and organic synthesis.

Since the turn of the century, continued research in the field of organic electrooptics (EO) has led to an enormous amount of progress in terms of bulk second-order nonlinear optical response. However, as of late, fundamental research in chromophore structure-property relationships and optimization of molecular hyperpolarizability through new approaches certainly does not get the consideration it is warranted despite having a significant contribution to the present success in the realm of EO. Guided through the use of sophisticated quantum mechanical modeling and classic design paradigms, materials were engineered in an attempt to further increase first-order hyperpolarizability (beta) above and beyond state-of-the-art materials through the use of novel heteroaryl-based electron donors and acceptors. The unprecedented degree of polarization in these neutral ground state chromophores, which resulted from lower ionization potentials and aromaticities, was extensively explored, both analytically and theoretically. In one new class of chromophores, an increase in electron-donor strength was off-set by the resistivity towards polarization caused by the divinylthienyl bridge. This led to an excellent balance in asymmetry and polarizability, and thus large beta. However, when these heteroaryl donors were incorporated into ring-locked tetraene bridges, the strong electron-donors were believed to have polarized the highly efficient bridges beyond optimal beta. Finally, ground work has been laid out for the application of all-optical, and optically assisted poling of a class of second generation, high beta, azo-based chromophores as an alternate means of improving poling induced order.