Second-order Nonlinear Optical Polymers Research Articles

Low half-wave voltage polymeric electro-optic modulator using CLD-1/PMMA for electrocardiogram (ECG) signal acquisition.

Electro-optic (EO) modulators are typically made of inorganic materials such as lithium niobate; the replacement of these modulators with organic EO materials is a promising alternative due to their lower half-wave voltage (Vπ), ease of handling, and relatively low cost. We propose the design and fabrication of a push-pull polymer electro-optic modulator with voltage-length parameters (VπL) of 1.28 V·cm. The device uses a Mach-Zehnder structure and is made of a second-order nonlinear optical host-guest polymer composed of a CLD-1 chromophore and PMMA polymer. The experimental results show that the loss is 1.7 dB, Vπ drops to 1.6 V, and the modulation depth is 0.637 dB at 1550 nm. The results of a preliminary study show that the device is capable of efficiently detecting electrocardiogram (ECG) signals with performance on par with that of commercial ECG devices.

Thermally crosslinkable second-order nonlinear optical polymer networks: high stability, good transparency, and large second-order nonlinear optical effects

A new in situ thermal crosslinking approach was proposed to design second-order nonlinear optical polymer networks through a simple synthetic route, with the combination of the “isolate chromophore” concept.

A TCBD-based AB2-type second-order nonlinear optical hyperbranched polymer prepared by a facile click-type postfunctionalization

A double click-type postfunctionalization strategy was successfully designed to prepare an AB2-type hyperbranched polymer containing highly polarizable tetracyanobutadienyl (TCBD)-based nonlinear optical chromophores.

Photo-crosslinkable second-order nonlinear optical polymer: facile synthesis and enhanced NLO thermostability

A new photo-crosslinkable second-order nonlinear optical system was designed and prepared by azido-yne and the thiol–ene click reactions.

The design of second-order nonlinear optical dendrimers: From “branch only” to “root containing”

Dendrimers are considered as a promising family of organic second-order nonlinear optical (NLO) polymers because of their well-defined structures, easily modified peripheral functional groups, interior branches and central cores. In order to obtain NLO materials with high performance, dendrimer structures have been optimized in the past years, such as the “branch only” and the “root containing” type dendrimers. This feature article highlights the achievements in exploring the rational design of dendrimers, partially marked by their macroscopic NLO performance.

Synthesis and Characterization of Novel Second-Order Nonlinear Optical Chromophore with Multi-Hydroxyl Groups Donor

ABSTRACTNew electro optical chromophore with 4-(bis(2-hydroxyethyl)amino)-2,6-dipropoxybenzaldehyde as electron donor was synthesized and characterized by 1H NMR spectra and mass spectra. Four hydroxyl groups were introduced to the electron donor, which could be easily reacting with carboxyl, isocyanate, anhydride, and so on, to afford us second-order nonlinear optical polymers. Chromophore T showed us good solubility in common solvents, thermal stability (above 200°C) and expected Uv-vis absorption. In this article, polymethyl methacrylate (PMMA) doped with chromophore T at different loading density was prepared to second- order nonlinear optical films by spin coating. These films showed us large second-order nonlinear optical coefficients, 13.5, 19.7, 24.3, and 26.4 pm/V for the second-order nonlinear optical films with chromophore loading density of 10 wt%, 20 wt%, 30 wt%, and 40 wt%, respectively.

Two second-order non-linear optical coordination polymers with noninterpenetrating honeycomb-like 2-D (6,3)-type networks

Two isostructural metal–organic frameworks, [ML(H2O)4]n (M = Y(II) (1) and Nd(II) (2)), NaH2L = 5-sulfoisophthalic monosodium salt), have been synthesized by hydrothermal reactions. Each metal is nine-coordinate with a distorted tricapped trigonal prismatic arrangement. L3− is a μ3 bridge to generate a homometallic 2-D noninterpenetrating (6,3) honeycomb-like topological network structure. The luminescence spectra indicate emission maxima at 406 and 402 nm, respectively. Compounds 1 and 2 show second-harmonic generation responses that are 0.5 and 0.8 times that of urea, respectively.

A novel second-order non-linear optical coordination polymer with three-fold interpenetrated CdSO4-type network constructed by carboxylate–sulfonate ligands and strontium ions

A novel strontium carboxylate–sulfonate coordination polymer, [Sr(HSIP)(H2O)3]n·nH2O (1) (NaH2SIP=5-sulfoisophthalic monosodium salt) has been synthesized by hydrothermal reaction. It was characterized by X-ray single crystal diffraction, infrared spectroscopy, elemental and thermogravimetric analysis. Each strontium atom is eight-coordinate with a distorted bicapped trigonal prismatic arrangement. The whole HSIP2− ligand acts as a η5μ4 bridge to generate three-fold interpenetrated CdSO4-type network structure, which is constructed from the left- and right-handed helixes paralleled to each other bridged by the HSIP2− ligands. The luminescence spectrum indicates an emission maximum at 459nm. Compound 1 shows a second harmonic generation (SHG) response that is 4 times that of KH2PO4.

Well-defined second-order nonlinear optical polymers by controlled radical polymerization, via multifunctional macromolecular chain transfer agent: Design, synthesis, and characterizations

To address the issue of the aggregation in second-order nonlinear optical (NLO) polymers we developed an approach based on the synthesis of a multifunctional macromolecular chain transfer agent. The controlled monomer insertion polymerization into the main chain by a ‘reversible addition-fragmentation chain transfer’ (RAFT) mechanism allows the spatial arrangement of the NLO chromophores along the polymeric chain in order to obtain sequence-ordered polymers. In a first step, a novel trithiocarbonate based macroinitiator containing the disperse red 19 (DR19) units in the main chain was synthesized by polycondensation; in a second step, this polymeric precursor was applied to the synthesis of a sequentially ordered polymer by controlled insertion radical polymerization of styrene. Size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) data revealed that, (i) for the first time, polystyrenes (PS) bearing DR19 dyes covalently bounded were obtained, and (ii) both the insertion reaction and the length of the polystyrene segments were accurately controlled. Whatever the incorporated dye amount, all the copolymers were soluble in common solvents. Second-order optical nonlinearity in corona-poled thin films was evaluated, and second harmonic coefficients up to 80 pm/V were determined for loading ratio lower than 10 wt-% (DR19/PS). This approach opens up opportunities for the incorporation of more efficient chromophores even in apolar matrices.

Second-order nonlinear optical hyperbranched polymer containing isolation chromophore moieties derived from both “H”-type and star-type chromophores

An NLO hyperbranched polymer (HP1) derived from both “H”-type and star-type chromophores was synthesized successfully for the first time with high yield via one-pot “A2 + B3” Suzuki polymerization reaction. Isolation chromophore was also introduced to further improve its performance. Although under the test conditions, the films of HP1 could not be poled completely, it still demonstrated satisfactory macroscopic NLO effect with the second harmonic generation (SHG) coefficient d 33 value of 36 pm/V.

Second-order nonlinear optical (NLO) polymers containing perfluoroaromatic rings as isolation groups with Ar/ArF self-assembly effect: Enhanced NLO coefficient and stability

Four new polyaryleneethynylenes P1–P4, which contained different aromatic or perfluoroaromatic isolation groups, were successfully prepared, via the palladium-catalyzed Sonogashira coupling reaction. Among them, P2, due to the presence of the self-assembly effect between the perfluoroaromatic and chromophore moieties, demonstrated much larger NLO effect (d33 value of 162.3 pm/V) and better stability with onset temperature for decay (111 °C). The research on the polymer conformation suggested that perfluorophenyl groups in different positions would result in different effects on the NLO coefficient, providing some useful information for the design of NLO polymers with better performance.

Click chemistry-based synthesis of azo polymers for second-order nonlinear optics

Four linear polymers containing pendant azo moiety were synthesized through click chemistry for second-order nonlinear optical study. The polymers were found soluble in most of the polar organic solvents such as tetrahydrofuran (THF), chloroform, and dimethyl formamide (DMF). The polymers showed thermal stability up to 300 °C and glass transition temperatures (Tg) in the range of 120–140 °C. The molecular weights (Mw) of these polymers (measured by gel permeation chromatography) were in the range 37,900–55,000 g/mol. The polymers were found to form optically transparent films by solution casting from THF solution. Order parameters were calculated from UV–vis absorption spectra. The morphology changes in the films after poling were characterized by atomic force microscopy. The angular dependence, temperature dependence, and time dependence of second harmonic generation (SHG) intensity were obtained by using 1064 nm Nd:YAG laser. The SHG intensity remained unchanged up to 95 °C. At room temperature, it remained stable up to 8 days after initial drop of about 14%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

New second-order nonlinear optical (NLO) hyperbranched polymers containing isolation chromophore moieties derived from one-pot “A2 + B4” approach via Suzuki coupling reaction

In this paper, a facile synthetic route was designed to prepare two new hyperbranched polymers HP1 and HP2 useful as second-order nonlinear optical (NLO) materials through a one-pot “A2 + B4” approach via a simple Suzuki coupling reaction. Thanks to the effect of the isolation chromophores to the main chromophore and the three-dimensional spatial isolation effect of the hyperbranched structure, these hyperbranched polymers demonstrated high second-harmonic generation coefficients (up to 73.6 pm V−1) and good optical transparency (with the maximum absorption as 466 nm in film).

Some new design strategies for second-order nonlinear optical polymers and dendrimers

Second-order nonlinear optical (NLO) materials have played a very important role in laser technology since the invention of the laser. The materials have been developed from inorganic crystals to organic molecules and polymers. The search for new second-order NLO materials with better performance has continuously been in the frontier of materials science and optical engineering. This article reviews some new design strategies for second-order NLO polymers, including dendronized polymers, dendrimers and hyperbranched polymers with the new concept of the “suitable isolation group”.

New second-order nonlinear optical polymers containing the same isolation groups: Optimized syntheses and nonlinear optical properties

Based on control experiments, a new series of second-order nonlinear optical polymers with fluorene moieties as isolation spacers were successfully prepared. In the polymers, the chromophore moieties were embedded into the polymer backbone with one position at the donor side, and another point in the π bridge. Different acceptors were used to construct the push–pull structure of chromophore moieties, including nitro groups, sulfonyl groups, 3-phenyl-5-isoxazolone, 1,3-diethylthiobarbituric acid and TCF groups. The tested NLO properties of the polymers demonstrated that the isolation groups with big size do not always benefit the resultant NLO effect. Also, for different acceptors, there should be different suitable isolation groups to balance the good and bad effects caused by the introduced isolation spacers.

Second-order nonlinear optical hyperbranched polymers via facile ring-opening addition reaction of azetidine-2,4-dione

A new hyperbranched polymeric structure was chosen as a nonlinear optical material. First, a difunctional chromophore, 4-(4′-nitrophenyl-diazenyl) phenyl-1,3-diamine (NDPD) was synthesized, which was then reacted with 4-isocyanato-4′(3,3-dimethyl-2,4-dioxo-azetidino)diphenylmethane (MIA) to form NDPDMIA (A 2 type monomer). The azetidin-2,4-dione functional groups exhibit selective reactivity, which can react only with primary amines under mild conditions. The hyperbranched polymers were synthesized via ring-opening addition reaction between azetidine-2,4-dione (A 2 type monomer) and primary amine (B 3 type monomer). This synthetic scheme comes with easy purification, high yield and rapid synthesis. Chemical structures of the hyperbranched polymers were characterized by FT-IR, 1H NMR, and elemental analysis. The inherent viscosity of hyperbranched polymers in DMSO ranged from 0.15 to 0.22 dLg −1. All of the obtained polymers were soluble in DMF, DMAc, and DMSO. Using in situ contact poling, r 33 coefficients of 6–16 pm/V and their temporal stability at 60 °C were obtained. Optical loss measurement was also achieved by a prism coupling setup.

Side-chain maleimide based electro-optic polymer for second-order nonlinear optics

The electro-optic properties of a poled second-order nonlinear optical maleimide polymer system were reported. This polymer was synthesized by doping disperse red 1 moieties into the maleimide system as the side chains. Its glass transition temperature was measured to be 202°C by Differential Scanning Calorimetry (DSC) technology. After being poled, the measured electro-optic coefficient of PHSD at the wavelength of 1550 nm is as large as 3. 03 pm/v. Except for an initial decay after being poled, PHSD exhibits little electro-optic relaxation in a long term and its electro-optic coefficient remains about 2. 46 pm/v after 15 days.

New photonic and electronic polymers

This paper gives an overview of recent work on new organic π-electron-conjugated materials prepared and tested in our laboratories. Second-order nonlinear optical polymers for electro-optic modulation were investigated, both guest–host and side-chain chromophoric materials. Chromophores and polymers were synthesized, thin films were prepared, and the following properties were measured: electro-optic coefficient, optical absorption loss and thermal stability. It was concluded that optical modulators fabricated from these materials could be viable components in optical communication systems. Work on novel polyphenylenevinylenes is summarized. Besides their low electrical resistivity, photoluminescent, and electro-active properties, these materials have interesting photoconductive properties that may prove useful in optical control of photonic logic devices.

A device-quality thermosetting polyurethane with improved processability and high thermal stability of dipole alignment for electro-optic applications

A device-quality second-order nonlinear optical (NLO) polymer prepared by post-functionalization of an epoxy-based precursor polymer exhibits an improved processability, such as good solubility in common organic solvents and excellent film-forming property. Toluene-2,4-diisocyanate as a cross-linking agent was used to cross-link the NLO polymer to create a three-dimensional (3D) network of polyurethane during poling. Using this thermosetting polyurethane, an electro-optic (EO) modulator based on attenuated-total-reflection (ATR) technology was fabricated successfully, and its performance was discussed. The highest EO coefficient of 16 pm/V for this modulator measured at a wavelength of 832 nm was obtained by an improved ATR method, and a high temporal stability of the poling-induced order was observed at elevated temperature up to 100 °C.

Electro-optically tunable photonic crystals

We report on electro-optical modulation with a sub-1-V sensitivity in a photonic crystal slab waveguide resonator which contains a nanostructured second-order nonlinear optical polymer. The electro-optical susceptibility in the core was induced by high electric-field poling. A square lattice of holes carrying a linear defect was transferred into the slab by electron-beam lithography and reactive ion etching, creating a photonic crystal slab-based resonator. Applying an external electric modulation voltage to electrodes leads to a linear electro-optical shift of the resonance spectrum and thus to a modulation of the transmission at a fixed wavelength based on the electronic displacement polarization in a noncentrosymmetric medium (Pockels effect). This effect is therefore inherently faster than other reported electro-optic modulation effects in nanophotonics.