Second-order nonlinear optical effects in novel side-chain liquid crystalline polymers and monomers under bias of an applied dc electric field

Second-order nonlinear optical susceptibilities of a series of newly synthesized liquid crystalline polymers and corresponding monomers were measured by using second-harmonic generation. A substituted stilbene moiety was selected as the main conjugated π-electronic structure, and systematic modifications were made at the site of the donor and in the conjugation path to compare the roles of various donors and charge-transferring linkages in the second-harmonic-generation process. The β values extracted from the measurements made on solutions and on thin films yielded similar values for the monomers and the corresponding polymers. The variations in β values are discussed in terms of molecular structural properties, charge-transferring power of the donors, and dispersion effect.