Synthesis of Dendridic NLO Chromophores for the Improvement of Order in Electro-optics
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Synthesis of Dendridic NLO Chromophores for the Improvement of Order in Electro-optics 1
Jessica Sinness, 1Olivier Clot, 1Scott R. Hammond,1Nishant Bhatambrekar, 1Harrison L. Rommel, 1Bruce Robinson, 2Alex K-Y. Jen, 1Larry Dalton. 1 University of Washington, Department of Chemistry, PO Box 173500, Seattle, WA 98195. 2 University of Washington, Department of Material Science and Engineering, PO Box 352120, WA-98195. ABSTRACT Previous research in organic electro-optics has shown dramatic increases in the hyperpolarizablity of NLO chromophores. However, this large microscopic activity has not been translated to the macroscopic domain. The polymeric electro-optic (E-O) materials continue to lack the high noncentrosymmetric order of the poled chromophores within the matrix necessary for high E-O response (r33). This deficiency of order represents one major obstacle that must be overcome before E-O device commercialization can be achieved. This lack of order is partially due to the large dipole moments of high µβ chromophores, which cause the chromophores to align in a centrosymmetric fashion through intermolecular electrostatic interactions. However, quantum calculations show that when the aspect ratio between the width and length of the chromophore system is adjusted to be greater than 1.4:1 by adding bulky side groups around the center of the chromophore, it would prevent side on pairing of the chromophores. This would cause a decrease in the large areas of centrosymmetric aggregation and thus allow for easier poling of the system. Here we report the synthesis of a nanoscale NLO architecture in which dendritic moieties have been incorporated around the center of the chromophore to give a three dimensional structure in order to achieve the 1.4:1 aspect ratio and maximize the macroscopic order of the system. INTRODUCTION Electro-optic modulators currently have the potential to have profound effect on the telecommunications industry and the speed with which we can send and receive information. These modulators allow for an electrical signal to be translated to a photonic signal that will carry this information significantly faster than its electronic counterpart. The key component of these modulators is that their optical properties vary under an electrical field. Lithium niobate (LiNbO3) is the current commercial standard but its speed limitations and high cost are forcing researchers to look for improved materials to convert electrical to optical signals more efficiently. One area that shows much promise is conjugated organic materials.[1] These conjugated organic chromophores generally consist of an electron donating group and an electron accepting group connected by a π-conjugated bridge. In the presence of an electrical field the π-electron density shifts from the donor to the acceptor, thus changing the index of refraction of the material. The ease of which the electrons can be shifted from the donor to the acceptor is measured by the hyperpolarizablity, or β. In order to fabricate an E-O device or charact
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