A Unified Description of Linear and Nonlinear Polarization in Organic Polymethine Dyes
An internal or external electric field F can drive the chemical structure, bond order alternation, and electronic structure of linear polymethine dyes from a neutral, bond-alternated, polyene-like structure, through a cyanine-like structure, and ultimately to a zwitterionic (charge-separated) bond-alternated structure. As the structure evolves under the influence of F, the linear polarizability α, the first hyperpolarizability β, and the second hyperpolarizability γ are seen to be derivatives, with respect to F, of their next lower order polarization (for α) or polarizability (for β and γ). These derivative relations provide a unified picture of the dependence of the polarizability and hyperpolarizabilities on the structure in linear polymethine dyes. In addition, they allow for predictions of structure-property relations of higher order hyperpolarizabilities.
© 1994 American Association for the Advancement of Science. 1 March 1994; accepted 6 June 1994. The research described in this report was performed in part by the Jet Propulsion Laboratory (JPL), California Institute of Technology, as part of its Center for Space Microelectronics Technology and was supported by the Advanced Research Projects Agency (administered by the Air Force Office of Scientific Research) and the Ballistic Missiles Defense Initiative Organization, Innovative Science and Technology Office, through a contract with the National Aeronautics and Space Administration (NASA). Work done at the Beckman Institute was supported by the National Science Foundation, the Air Force Office of Scientific Research, and the North Atlantic Treaty Organization. G.B. thanks the National Research Council and NASA for a Resident Research Associateship at JPL. The work in Mons is carried out within the framework of the Belgium Prime Minister Office of Science Policy "P6le d'Attraction Interuniversitaire en Chimie Supramol6culaire et Catalyse" and "Programme d'Impulsion en Technologie de l'Information" and is supported in part by the Belgium National Fund for Scientific Research (FNRS). We thank K.-T. Lim, B. G. Tiemann, D. N. Beratan, and L.-T. Cheng for helpful discussions.