Functionalized Guanidines for Electro-Optic Materials.

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Functionalized Guanidines for Electro-Optic Materials. Nicholas Buker, Kimberly A. Firestone, Marnie Haller1, Lafe Purvis, David Lao, Robert Snoeberger, Alex K.-Y. Jen1, Larry R. Dalton University of Washington Dept of Chemistry Box 351700 Seattle, WA 98195 1 Univeristy of Washington Dept of Materials Science and Engineering ABSTRACT A family of nonlinear optical chromophores has been synthesized containing novel donor systems based on functionalized guanidines. Chromophores utilizing these donor systems display superior transparency and stability properties. The unusual and highly desirable characteristics of these chromophores make them very promising candidates for electro-optic applications. Systematic study of the molecular hyperpolarizabilities and bulk electro-optic properties of polymers containing these chromophores is being used to guide optimization of these systems. INTRODUCTION The variable refractive index of electro-optic (EO) materials has led to a great deal of research interest. Application of an electric field to EO materials leads to a linear variance in refractive index known as Pockel’s effect. When incorporated into devices, these materials serve as an effective vehicle for rapid modulation of optical signals using electrical inputs. Nonlinear optical (NLO) chromophores are the most successful family of organic EO materials. These chromophores are typically comprised of a delocalized π-electron system that connects electron rich moieties (donors) to electron deficient functionalities (acceptors). Hyperpolarizability (β), is the component of molecular NLO behavior that is responsible for EO effects. Optimization of NLO chromophores has proven to be a challenging task because enhancement of β typically results in reduced stability, decreased transparency to telecommunication wavelengths and other unwanted consequences.[1,2] A great deal of effort has been devoted to modification of bridges and acceptors, but donors have been largely neglected. Systems based on oxygen and sulfur have been explored, but the former proved to perform poorly while the latter suffers from stability problems.[1] The standard dialkyl and diaryl amino donor systems have been successful, but evidence suggests that superior systems exist.[3,4] These unconventional guanidine and phosphorous based donor systems demonstrate a significant enhancement of µβ values in small chromophores in conjunction with high degrees of thermal stability. Literature suggests that integration of these improved donors into modern chromophore molecules should yield significant improvements to β resulting in increased r33 values and enhanced device performance without sacrificing stability or transparency.[3,4]

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RESULTS The enhanced µβ values, good transparency properties, and high thermal stabilities reported in the literature motivated the decision to further explore these novel donor structures. Reported chromophores consisted only of simple donor-acceptor designs, lacking good bridge systems or advanced acceptors.[3,4] Numer