Focused Microwave-assisted Synthesis of 2,5-Dihydrofuran Derivatives as Electron Acceptors for Highly Efficient Nonlinea
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L10.48.1
Focused Microwave-assisted Synthesis of 2,5-Dihydrofuran Derivatives as Electron Acceptors for Highly Efficient Nonlinear Optical Chromophores Sen Liu, Marnie A. Haller, Jingdong Luo, Sei-Hum Jang, Hong Ma, Larry R. Dalton, and Alex K.-Y. Jen* Departments of Materials Science and Engineering and Chemistry University of Washington Seattle, WA 98195 ABSTRACT A diversified family of 2,5-dihydrofuran derivatives has been synthesized as a new class of highly efficient and tunable electron acceptors using the single-mode focused microwave irradiation. High poling efficiency and very large electro-optic coefficients (r33 values of 128 and 116 pm/V at 1.3 µm) have been demonstrated using 2-dicyanomethylen-3-cyano-4,5,dimethyl-5-trifluoromethyl-2,5-dihydrofuran (CF3-TCF)-based chromophores as dopant in poly(methyl methacrylate) (PMMA) and a high glass-transition temperature polyquinoline (PQ100) respectively. Excellent dipole alignment stability has also been demonstrated in the guest/host composite at 85°C. Multi-functionalized NLO chromophores based on hydroxy containing 2,5-dihydrofuran acceptors were also synthesized through microwave methodology for further characterizations. INTRODUCTION Distinguishing themselves from the full-fledged inorganic crystals in commercial devices, polymeric electro-optic (EO) materials have shown great potential for applications in high-speed photonic devices due to their large EO coefficients (r33), ultra-fast response time, and ease of integration.1 In general, the macroscopic EO response of a polymer is induced by aligning the dipole of nonlinear optical (NLO) chromophores via a high external electric field to create noncentrosymmetry.2 In the past decade, the search for EO polymeric materials with very large r33 values has led to extensive efforts in exploring “push-pull” type chromophores with high dipole moment (µ) and molecular nonlinearity (β). Among three molecular building blocks commonly used for NLO chromophores, the development of electron donors and conjugating bridges is already quite mature that they can meet most of the synthetic and material requirements.3 Therefore, the major task for optimizing µβ value of a chromophore has been focused on developing novel electron acceptors. RESULTS AND DISCUSSION Synthesis of 2,5-dihydrofuran acceptors and NLO chromophores Recently, several electron-deficient heterocyclic compounds have emerged as strong electron acceptors for nonlinear optics.4 Among them, an unconventional 2-dicyanomethylen-3cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF)-based chromophore has been reported that possesses an exceptionally large µβ value.5 In light of this development, the 2,5-dihydrofuran derived structure has been extensively studied to further enhance its electron-accepting strength for NLO chromophores. However, the synthetic methodology commonly adopted to prepare TCF acceptor is a concerted process. The reaction can not be conducted through a step-wise manner to isolate the key intermediate, a cyclized imine, 2-imino-3-cyano-4,5,5-trimeth
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