SHG Characterization of Different Polar Materials Obtained by in Situ Photopolymerization

The structural, thermal, and nonlinear optic (NLO) characterization of different polar materials is reported. These materials, which range from side-chain polymers to anisotropic networks and gels, were prepared by in situ photopolymerization of their precursors in the ferroelectric SmC* liquid crystal phase. The influence of the structure, the percentage of cross-linker, and the degree of mobility of a common NLO-phore on the second harmonic generation (SHG) activity have been considered with the aim of analyzing the most suitable approach for practical applications. Slight improvements in the SHG d ij coefficients of these polymeric materials compared to their parent low molecular mass starting compounds have been observed. However, from these studies, it can be stated that side-chain polymers and low cross-linking polymers are the most interesting materials from the point of view of both the NLO-activity and the ease of synthesis. These two types of materials provide stable room temperature thin films displaying SHG and electrooptic (EO) responses without the application of a poling field.