Structure-property studies on systematically synthesized and processed organic materials: Guidance for designing novel optoelectronic materials

Organic/polymeric nonlinear optical materials have emerged in recent years as promising candidates for optical signal process and optoelectronics because of their extraordinary optical, structural, and mechanical properties. One of the most commonly used approaches during the molecular design is to optimize both the backbone and the pendant functional groups of the polymer. However, the theoretical guidance for such molecular design is very limited. In this case, experimental studies on systematically built and sequentially derivatized model compounds can play a major role in identifying structural features for enhancing the processibility and the third-order nonlinearity of polymers.;This thesis starts with the synthesis of a few series of model compounds. These compounds are: (i) thiophene oligomers (trimer through hexamer); (ii) ;It is followed by the material processing (using various thin film techniques), material characterization, and measurements of third-order optical nonlinearities, ;When compounds have either one-photon or two-photon absorption at experimental wavelength, a new theoretical model is developed to consider the DFWM signal as two dynamic processes. One is the coherent four-wave mixing which is contributed from the molecules in the ground states. The other is the population grating process which is contributed by the molecules in the excited states. Both processes are believed to be enhanced by either one-photon or two-photon resonances, but involve different dynamic response.