Synthesis and Characterization of Third Order Nonlinear Optical Materials

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SYNTHESIS AND CHARACTERIZATION OF THIRD ORDER NONLINEAR OPTICAL MATERIALS L. P. YU*, M. CHEN* and L. R. DALTON*, X. F. CAO**, J. P. JIANG** and R. W. HELLWARTH** *Department of Chemistry, University of Southern California, Los Angeles, CA90089; "**Department of Electrical Engineering and Physics, University of Southern California, Los Angeles, CA-90089. ABSTRACT New polymers incorporating a variety of electroactive moeities with defined n-electron conjugation lengths have been synthesized and characterized by degenerate four wave mixing (DFWM) techniques. The X(3 )/(x values for these materials varied from 10-12 to 10-13 esu cm. This work has identified several promising structures with nonlinear optical activity including organometallic and purely organic materials. The preparation of composite materials has also permitted the measurement of X(3 )/ax as a function of the electroactive unit concentration. INTRODUCTION Nonlinear optical (NLO) properties of polymers is a rapidly growing research field because of the many practical applications of polymeric materials in optoelectronic devices. 1 Polyconjugated materials like polydiacetylene, polyacetylene and polythiophene have been heavily investigated. 1 -3 But the inherent deficiencies of these materials, such as poor solubility, poor thermal and environmental stability and high optical absorption losses, prevent their use in practical applications. Therefore, new materials must be found. Both theory and experiment have demonstrated that polymers with limited conjugated length can manifest NLO effects as large as polymers with extended polyconjugation.4- 6 It has been recognized that electron delocalization and charge transfer contribute to NLO effects, and that polymers with electron clouds of enhanced anharmonicity are expected to give rise to large NLO effects. 3,7 Therefore, it is reasonable to test different materials with different kinds of constituents for optical nonlinearities. Such materials would include those containing transition metals and polymers with ionic or with charge separated

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Abbreviations: Fourier Transform Infrared (FTIR), Nuclear Magnetic Resonance (NMR), Ultraviolet/visible (UV/vis), Gel Permeate Chromatography (GPC), Differential Scanning Caloriometer (DSC), Dimethylformamide (DMF), Dimethylsulfoxide (DMSO). Mat. Res. Soc. Symp. Proc. Vol. 173. ©1990 Materials Research Society

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species. With this in mind, we have extended our research to a broader survey of conjugated electroactive units. Here we report part of our effort in the synthesis and characterization of new materials exhibiting large optical nonlinearities. EXPERIMENTAL 6 Polymer 1. This polymer was synthesized through a precursor polymer. The mixture of prepolymer (0.904 g, 1.97 mmol) with nitrobenzene (20 mL) and benzoyl chloride (3 mL) was refluxed for 4 hrs. The reaction mixture was poured into methanol (50 mL) and the red precipitate was collected by filtration and washed with methanol unti

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