Infrared Photorefractive and Light-Emitting Polymers for Optical Technologies

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Objectives. We propose an experiment - theory effort focused on the development of two classes of multifunctional organic materials to be used for information technologies. The first class of ma-terials consist of infrared compatible photorefractive polymers that are suitable for reconfigurable filters, switches and interconnects. The second class of materials are pi-conjugated polymers with emission in the infrared. This effort will capitalize on our past experience in developing photorefrac-tive and light emitting polymers through a combination of many-body calculations incorporating electron-electron interactions on these materials and the characterizations of their electrical and nonlinear optical properties. The operation of existing photorefractive and light emitting polymers is restricted to the visible region of the spectrum which prevents their use in telecommunication.Approach. To extend the spectral sensitivity of photorefractive polymers to the infrared we will use multiphoton absorption to generate photoconductivity from high energy two-photon excited states in either a pi-conjugated polymer matrix or an electro-active chromophore dopant. Theo-retical work will be performed in identifying two-photon states from which enhanced photogener-ation efficiency is expected. These results will also guide the design of one-photon photorefractive polymers with sub-millisecond response time. The search for pi-conjugated polymers with photo-luminescence in the infrared will build on our recent discovery of the principle that excited state ordering conducive to light emission at low frequencies is obtained in pi-conjugated polymers with large molecular unit cells. The specific structural requirement is that there exists molecular conju-gation transverse to the direction of conjugation along the polymer chain, leading to longitudinal confinement and transverse delocalization of the optical exciton. Experimental studies will be con-ducted on soluble derivatives of poly(isothianaphthene), which satisfy the structural requirement for infrared emission.Significance and Impact. The proposed infrared compatible photorefractive and light emitting polymers will enable new devices for telecommunication technologies. In spite of the rapid advances made in the area of organic optoelectronics, existing organic materials amid devices operate largely in the visible region of the electromagnetic spectrum. Our work will extend the spectral range of applications, and it is expected that the outcomes of our research will have strong impact on the device physics of organic materials. The aim is not to compete with the technology utilizing con-ventional inorganic semiconductors, but to develop new functionalities and applications, utilizing the unique processing capability of organic materials. Importantly, the strong coupling between experiment and theory will lead to enhanced understanding of the fundamental processes of photo-generation, multiphoton absorption and light emission in organics, an area that is still in its infancy. Finally, the proposed research provides a unique multidisciplinary framework to integrate research and teaching. Students working on the project are exposed to chemistry, optics, engineering, and the fundamental physics of nonlinear absorption, charge-injection, charge- and energy-transfer, and light emission.