Photorefractive Materials

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9815955YuIn this proposal, the principles of designing novel, high performance photorefractive materials are sought. Two classes of photorefractive materials are proposed: 1) high and or low Tg, fully functionalized photorefractive polymers and 2) multifunctional small molecular systems. These are presented to test the idea that conjugated polymer backbones will play the role of charge transport agent and the neutral transition metal complexes (which exhibit interesting metal-to-ligand charge transfer (MLCT) processes) will play the role of charge generating species. In this way, the quantum efficiency of thecharge generation process can be enhanced and the dark current and local ionic dipole field can be minimized. Thus, the PR performance of resulting polymers will be enhanced. The glass transition temperatures of proposed polymer system can be fine-tuned so that PR polymers with either dominating Pockel contribution or Kerr contribution can be synthesized and their physical properties compared. Different parameters which affect the PR performance, such as variations of NLO chromophores, sensitizers and alkyl chains spacers, will be systematically investigated and their structure/property correlations defined. The second class of materials are amorphous, low Tg small molecular systems. They are single multifunctional molecules containing all of the functionality necessary for PR effect. One of such systems is the oligothiophene-NLO molecules: amorphous materials where the oligothiophene is the photoconductive component. These materials are designed to test the idea that a multifunctional small molecular system, instead of polymers, may exhibit comparable PR performances. These are structurally well defined, and simple systems for detailed physical studies. An extra bonus is that they are also very easily processed into thick films. Coupled with the proposed synthetic work, the detailed physical characterization of these materials will be carried out, including e-o measurements, photoconductivity studies, mobility measurements, two beam coupling and four wave mixing experiments and holographic imaging. %%%The significance of the proposed work is that it provides novel thinking in new material design and synthesis. The idea of introducing metal complexes into functional polymers may prove vital for future material development other than the photorefractive polymer system. The idea of a multifunctional small molecular system for photorefractive effect is also important both for fundamental understanding of the PR mechanism and for practical applications. The novel chemistry developed in the synthesis of these materials will impact the polymer synthetic community.***