This contribution details the synthesis and chemical/physical characterization of a series of unconventional twisted pi-electron system electro-optic (EO) chromophores. Crystallographic analysis of these chromophores reveals large ring-ring dihedral twist angles (80-89 degrees) and a highly charge-separated zwitterionic structure dominating the ground state. NOE NMR measurements of the twist angle in solution confirm that the solid-state twisting persists essentially unchanged in solution. Optical, IR, and NMR spectroscopic studies in both the solution phase and solid state further substantiate that the solid-state structural characteristics persist in solution. The aggregation of these highly polar zwitterions is investigated using several experimental techniques, including concentration-dependent optical and fluorescence spectroscopy and pulsed field gradient spin-echo (PGSE) NMR spectroscopy in combination with solid-state data. These studies reveal clear evidence of the formation of centrosymmetric aggregates in concentrated solutions and in the solid state and provide quantitative information on the extent of aggregation. Solution-phase DC electric-field-induced second-harmonic generation (EFISH) measurements reveal unprecedented hyperpolarizabilities (nonresonant mubeta as high as -488,000 x 10(-48) esu at 1907 nm). Incorporation of these chromophores into guest-host poled polyvinylphenol films provides very large electro-optic coefficients (r(33)) of approximately 330 pm/V at 1310 nm. The aggregation and structure-property effects on the observed linear/nonlinear optical properties are discussed. High-level computations based on state-averaged complete active space self-consistent field (SA-CASSCF) methods provide a new rationale for these exceptional hyperpolarizabilities and demonstrate significant solvation effects on hyperpolarizabilities, in good agreement with experiment. As such, this work suggests new paradigms for molecular hyperpolarizabilities and electro-optics.

Ultralarge Hyperpolarizability Twisted π-Electron System Electro-Optic Chromophores: Synthesis, Solid-State and Solution-Phase Structural Characteristics, Electronic Structures, Linear and Nonlinear Optical Properties, and Computational Studies

Publisher Summary Over the past 15–20 years, the non-linear optical (NLO) response of organic molecules has been of wide interest to organic and physical chemists, as well as physicists and chemical engineers. This interest arises from the possible use of such organic materials. In principle, photonics or the hybrid technology optoelectronics, both based on non-linear optical phenomena, can supersede electronics in communication technology. These technologies allow many operations that are currently effected with electron conduction to be replaced by operations based on light conduction. Many problems are encountered when it comes to the translation of a molecular property into a bulk property. It has transpired that some of these problems are not easy to solve with classical NLO-phores that mostly belong chemically to the class of merocyanine dyes. New design strategies for organic molecules and their respective bulk structures, crystals or oriented composite materials like polymers, are needed. Only a more fundamental understanding of these issues will allow rational optimization of molecular and bulk properties. This chapter surveys second-order molecular polarizabilities of organic molecules. Emphasis is given to the underlying of physical principles of non-linear optics (e.g. molecular topology), and to the establishment of structure–property relationships.

Organic Materials for Second-Order Non-Linear Optics

Highly Efficient Carbazole-π-Dimesitylborane Bipolar Fluorophores for Nondoped Blue Organic Light-Emitting Diodes†

This review article describes recent developments in the field of second-order nonlinear optical (NLO) polymers with specific focus on their characterization methods, materials synthesis, chromophore orientation techniques, and device applications. For the characterization techniques of NLO properties of organics and polymeric materials, electric field-induced second harmonic generation, hyper-Raleigh scattering, electro-optic coefficient measurement, etc. are discussed. The significant progress obtained from the authors’ investigations, resulted in various types of polymeric materials including dendrimers and organic-inorganic hybrids with specific structures of academic and technological significance which are presented here. To produce highly efficient macroscopic nonlinearity in NLO polymeric systems, several chromophore orientation techniques such as static field poling, photoassisted poling, all optical poling, contact and corona poling are also demonstrated. In addition, the prospects for practical applications of the NLO polymers in information technology are reviewed.

Polymeric Materials and their Orientation Techniques for Second-Order Nonlinear Optics

An extensive series of conjugated (porphinato)zinc(II)-based chromophores featuring nitrothiophenyl and nitrooligothiophenyl electron-accepting moieties has been synthesized using metal-catalyzed cross-coupling reactions involving [5-bromo-15-triisopropylsilylethynyl-10,20-diarylporphinato]zinc(II) and an unusual electron-rich Suzuki-porphyrin synthon, [5-(4-dimethylaminophenylethynyl)-15-(4‘,4‘,5‘,5‘-tetramethyl[1‘,3‘,2‘]dioxaborolan-2‘-yl)-10,20-diarylporphinato]zinc(II), with appropriately functionalized aryl and thienyl precursors. These donor−acceptor chromophores feature thiophenyl, [2,2‘]bithiophenyl, and [2,2‘;5‘,2‘ ‘]terthiophenyl units terminated with a 5-nitro group; one series of structures features these acceptor moieties appended directly to the porphyrin macrocycle meso-carbon position, while a second set utilizes an intervening meso-ethynyl moiety to modify porphyrin-to-thiophene conjugation. The dynamic hyperpolarizability of these compounds was determined from hyper-Rayleigh light scatte...

Design, Synthesis, Linear, and Nonlinear Optical Properties of Conjugated (Porphinato)zinc(II)-Based Donor−Acceptor Chromophores Featuring Nitrothiophenyl and Nitrooligothiophenyl Electron-Accepting Moieties

A series of symmetric derivatives of 4-(dicyanomethylene)-2-methyl-6-(p-(dimethylamino)styryl)-4H-pyran (DCM laser dye) has been synthesized, and the nonlinear optical properties and thermal decomposition temperatures of each of the chromophores has been measured. The symmetric chromophores all have larger hyperpolarizabilities than one would expect based on their absorption maxima. Estimations of their oscillator strengths based upon UV/vis spectra are all well above 1.0. It is proposed that these compounds possess two excited electronic states close to each other in energy, both contributing to the hyperpolarizability in an additive fashion. Electro-optical absorption spectroscopy data and semiempirical calculations on a model compound support this hypothesis. The implications of these results with regard to the tradeoff between nonlinearity and transparency are discussed. The large dipole moments and high decomposition temperatures of these chromophores make them attractive candidates for use in electr...

(dicyanomethylene)pyran derivatives with c2v symmetry : an unusual class of nonlinear optical chromophores

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(dicyanomethylene)pyran derivatives with c2v symmetry : an unusual class of nonlinear optical chromophores