Theory-Inspired Development of Organic Electro-optic Materials

Abstract

Correlated time-dependent density functional theory (TDDFT) quantum mechanical and pseudo-atomistic Monte Carlo (PAMC) statistical mechanical methods have been used to assist in the understanding of and to guide the improvement of organic electro-optic (OEO) materials, prepared by electric field poling of pi-electron chromophore-containing materials near their glass transition temperature. Theoretical treatment of the effects of dielectric permittivity and optical frequency on molecular (chromophore) first hyperpolarizabilities has been carried out as well as the analysis of the influence of spatially anisotropic intermolecular electrostatic interactions on the poling-induced noncentrosymmetric order of chromophores. Three classes of OEO materials have been considered in correlated theoretical and experimental investigations: (1) traditional chromophore/polymer composite materials, (2) chromophores covalently incorporated into polymers, dendrimers, and dendronized polymers, and (3) recently discovered materials consisting of chromophores incorporated into chromophore-containing host materials. This latter class of materials is referred to as binary chromophore organic glasses (BCOGs). These BCOGs exhibit exceptional electro-optic activity because of a combination of high chromophore number density, the effect of high dielectric permittivity on molecular first hyperpolarizability, and improved acentric order arising from the intermolecular electrostatic interactions among the two types of chromophores. The electrical conductivity of materials can also influence achievable electro-optic activity, and thin metal oxide buffer layers, introduced to limit charge injection, can significantly improve poling efficiency. Chromophore order can also be influenced, in some cases, by novel processing techniques, such as laser-assisted electric field poling. Thermal and photostability are important parameters for practical application of materials and have been improved dramatically in recent times. Diels-Alder and fluorovinyl ether cycloaddition reactions have been used to elevate final material glass transition temperatures to above 200 degrees C. Photostability is dominated by the photoactivation of singlet oxygen and subsequent attack on electro-optic chromophores. Photostability can be improved by more than 4 orders of magnitude by chromophore modification and material packaging.

High-Speed, Low Drive-Voltage Silicon-Organic Hybrid Modulator Based on a Binary-Chromophore Electro-Optic Material

“…Each EO substructure comprises one electro-optic core with functional sidegroups (blue) that lead to a define three-dimensional dendron structure with spherical shape. The site-isolation groups (blue) decrease intermolecular interaction and thereby reduce head-to-tail orientation of neighboring molecules, while the spherical shape results in an enhancement of poling effi ciency [32].…”

Emergent Properties in Locally Ordered Molecular Materials

“…[44][45][46][47] Specifically, the linear and nonlinear (hyper)polarizabilities of organic chromophores have attracted attention for use in sum frequency generation, optical switching, and signal processing. [44,48] Closely related to polarizability is the dielectric response, and the dielectric constant of a material is crucial for applications in biology, [45][46][47]49,50] sensors, [51,52] electron transfer, [53,54] and electronics. [55][56][57] For example, the dielectric constant of the gate insulating material controls the operating voltage of field-effect transistors.…”

Synthesis of Binaphthyl-Based Push-Pull Chromophores with Supramolecularly Polarizable Acceptor Ends

“…Second harmonic generation (SHG), a nonlinear optical property which is at the foundation for advanced technologies in materials science and biological imaging, requires a fully conjugated organic structure at the molecular level and the absence of a center of symmetry in the bulk [2][3][4][5][6]. Centrosymmetrical molecules need stringent conditions in the self-assembly process in order to generate efficient materials for SHG [7,8].…”