Novel nonlinear optical polymers with crosslinkable functional groups

Summary Monomers with non linear optical (NLO) and photocrosslinkable (cinnamate) active side group have been synthetized. The study of their copolymerization has shown that a third monomer is necessary to increase the yield of copolymerization from 9% to 53%. The monomers reactivity ratios were estimated to be close to each other. Glass transition temperatures are relatively high though inherent viscosities of the terpolymer are low.     

Second-order nonlinear optical response of thin films containing organic chromophores. Theoretical aspects

This paper discusses some theoretical aspects associated with the unusual second-order nonlinear optical response of chromophoric self-assembled stilbalzolium superlattices, and of (N,N-dimethylamino)-4-nitrostilbene (DANS)-doped glass polymers poled in an “in-plane” configuration. It is found that the bulk nonlinearity of such materials strongly depends upon specific chromophore interactions. While for the stilbalzolium superlattices the supramolecular hyperpola-rizability is strongly affected by the ion-pair configuration, the formation of (formally) centrosymmetric charged chromophore aggregates is likely responsible for the observed anomalous strong nonlinearity in DANS-doped in-plane poled polymers. The simple “chromophore gas” model is thus inadequate to describe the non-linearity of such materials.     

Synthesis and characterization of two novel functional ladder-like polysilsesquioxanes for nonlinear optical response

Two novel functional ladder-like polysilsesquioxanes with double-chain macromolecular backbones and nonlinear optical (NLO) chromophore-containing side chains for NLO applications (NLO-T₁ and NLO-T₂) were synthesized successfully for the first time via the introduction of the NLO chromophores to the side chains of the ladderlike polychloropropylsilsesquioxane (Cl-T₁) and ladderlike poly(4-chloromethylphenyl)ethylsilsesquioxane (Cl-T₂), respectively, by an etherification reaction. The obtained polymers were characterized by FTIR, ¹H NMR, ¹³C NMR, ²⁹Si NMR, X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vapour pressure osmometry (VPO), fluorescence spectroscopy and second-harmonic generation (SHG) measurements. The poled thin films of the above two ladder-like NLO polymers showed d₃₃ coefficients of 9.2 and 9.6 pm V⁻¹, respectively. Compared with the corresponding single main chain polymers, the poled thin films of the synthesized ladder-like NLO polymers demonstrated a much higher thermal stability of SHG.     

A strong tracking predictor for nonlinear processes with input time delay

Nonlinear state prediction is of crucial importance to design controllers for nonlinear processes with input time delay. In this paper, the extended nonlinear state predictor (ENSP) we proposed is first outlined, which is used to predict the future states of a class of nonlinear processes with input time delay. A new concept of strong tracking predictor (STP) is then proposed, and an orthogonality principle is given as a criterion to design the STP. On the basis of the orthogonality principle, the ENSP is modified, which results in a STP. After the detailed STP algorithm is presented, we prove that the STP is locally asymptotically convergent for a class of nonlinear deterministic processes if some sufficient conditions are satisfied. In the presence of measurement noise, it is further proved that the proposed STP is exponentially bounded under certain conditions. Finally, computer simulations with a MIMO nonlinear model are presented, which illustrate that the proposed STP can predict accurately the future states of a class of nonlinear time delay processes no matter whether the states change suddenly or slowly, in addition, it has definite robustness against model/plant mismatches.     

Switchable nonlinear optical metallochromophores with pyridinium electron acceptor groups

Organotransition metal complexes have much to offer as nonlinear optical (NLO) chromophores since they allow large hyperpolarizabilities to be combined with various other physical properties in an unparalleled diversity of molecular structures. This Account summarizes our synthetic chemistry driven investigations in the NLO research field, which have focused primarily on complexes of ruthenium, and to some extent iron. A number of fascinating discoveries are described, including the first demonstration of redox-induced switching of NLO behavior and chromophores which disobey the otherwise universal rule that elongation of polyene systems leads to continual increases in quadratic NLO responses.     

New hyperbranched polymers containing second-order nonlinear optical chromophores: Synthesis and nonlinear optical characterization

Three hyperbranched polymers (P1-P3) containing second-order nonlinear optical chromophores were synthesized by copolymerization of aromatic dialdehydes (carbazole, triphenylamine or benzene moieties) with sulfonyl-based chromophores attached with three active methylene groups, from “A₂ + B₃” approach based on simple Knoevenagel reaction. For comparison, their corresponding linear analogue polymers (P4-P6) were prepared. All the polymers are soluble in common organic solvents, and exhibit good thermal stability. The tested NLO properties of the hyperbranched polymers are better than their corresponding linear polymers, due to the three-dimensional spatial separation of the chromophores in the obtained hyperbranched polymeric structures.     

Boosting piezoelectric response of KNN-based ceramics with strong visible-light absorption

A series of (1 − x)(K_0.48Na_0.52)NbO₃-x(Bi_0.5Na_0.5)(Zr_0.55Ni_0.45)O_3-δ (KNN-BNZN) ceramics are designed to achieve excellent piezoelectric response along with narrow bandgap. The ceramics with x = 0.04 exhibit unprecedented piezoelectric coefficient d₃₃ ~ 318±10pC N⁻¹ in comparison with all reported narrow bandgap ceramics. A rhombohedral-orthorhombic-tetragonal (R-O-T) phase boundary is observed, indicating the formation of defect dipoles (Ni²⁺-) at morphotropic phase boundary region is desirable for piezo-/ferroelectric properties. In addition, a narrow bandgap ~2.5 eV along with gap states (~0.9 eV and ~1.6 eV) is obtained from the ceramics when x > 0.02, which can be persuasively explained by the schematic plot of bandgap splitting mechanism proposed in this work, where Ni 3d energy state plays a role as a scaffold in the process of electron transition. More importantly, largely enhanced photovoltaic performance of the ceramics is achieved under AM 1.5 irradiation. The NIR photoresponse property (maximum current density of ~100 nA cm⁻²) indicates such KNN-based ceramics with sub bandgap ~ 0.9 eV may even have potential to be applied in NIR light-activated devices. Our findings might pave way for the further development of piezoelectric/photoresponsive multifunctional devices.     

Carbon nanotubes for optical limiting

This paper reviews the optical limiting properties of carbon nanotubes. The nonlinear optical properties of nanotubes were investigated in water and in chloroform suspensions. Nonlinear transmittance measurements were reported for various pulse durations and wavelengths and show that carbon nanotubes are good candidates for effective optical limiting over broad temporal and laser energy ranges. Z-Scans and pump-probe time-resolved experiments were achieved to identify the origin of optical limiting in nanotubes. The main phenomenon is a strong nonlinear scattering, originating from solvent vapour bubble growth and sublimation of nanotubes at high fluences. Heat transfer from particles to solvent is particularly effective as compared to carbon black suspensions because of the large surface area of the carbon nanotubes.     

Modeling nonlinear viscoelastic response

We present a model for calculating nonlinear viscoelastic response which we call the “phases model” (PHM). In terms of a mechanical model representation the PHM is a generalized Maxwell model with nonlinear elements where each Maxwell element is referred to as a phase. The viscous material properties are represented in the model in terms of flow curves of the individual phases. The collection of flow curves form the flow diagram. We show how to calibrate the flow diagram from a family of constant rate test curves by means of a simple straightforward procedure. We give an example of such a calibration for a certain rigid polyurethane. We applied our model to the calculation of nonlinear viscoelastic response to varius loading programs in uniaxial tension, and to the creep of a simply supported beam, and obtained good agreement with experimental data.     

非线性光学材料研究现状与应用前景

作者从无机材料、有机材料、高分子材料、无机/有机复合材料、金属有机材料5个方面对非线性光学材料进行了分类综述,介绍了非线性光学材料的发展历程;讨论了它们的非光学性质、特点,并将有机非线性光学材料与无机非线性光学材料作对比,分别介绍了各自的优势与不足,展望了非线性光学材料的发展前景.     

Synthesis and optical properties of polyacetylenes containing nonlinear optical chromophores

High molecular weight polyacetylenes bearing nonlinear chromophoric pendants poly[4-ethynyl-4′-(N,N-diethylamino)azobenzene-co-phenylacetylene]s [poly(EAAB-co-PA)s] were synthesized in moderate yields by [Rh(nbd)Cl]₂-Et₃N. The azo unit in the copolymers can be effectively controlled by the monomer feed ratio. Whereas the homopolymer of EAAB possessed low solubility, all the copolymers, however, dissolved readily in common organic solvents when the poly(EAAB) molar content was less than 41.7%. The structures and properties of the polymers were characterized and evaluated by UV, NMR, optical limiting, and nonlinear optical analyses. All the copolymers possessed high stereoregularity and thermal stability (≥300 °C). They can attenuate intense laser pulses, with solutions of high concentrations showing better performances. The third-order nonlinear susceptibility of the copolymers was as high as 4.62×10⁻¹¹ esu, which are two orders of magnitude larger than those of poly(PA), and larger than that of poly(N-carbazoylacetylene), and poly(1-naphthylacetylene).     

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.     

Carbon black thin films with tunable resistance and optical transparency

Layer-by-layer assembly was used to produce highly conductive thin films of carbon black and polymer. Positively and negatively-charged polyelectrolytes, polyethylenimine (PEI) and poly(acrylic acid) (PAA), were used to stabilize carbon black in aqueous mixtures that were then deposited onto a PET substrate. The effects of sonication and pH adjustment of deposition mixtures on the conductivity and transparency of deposited films was studied, along with drying temperature. Sonication and oven drying at 70 °C produced films with the lowest sheet resistance (∼1500 Ω/sq), which is a bulk resistivity below 0.2 Ω cm for a 14-bilayer film that is 1.3 μm thick. These two variables improve packing and connectivity amongst carbon black particles that results in increased electrical conductivity. Increasing the pH of the PAA-stabilized mixture and decreasing the pH of the PEI-stabilized mixture resulted in transparent films due to increased polymer charge density. These pH-adjusted films have much higher sheet resistance values than their non-adjusted counterparts due to their reduced thickness and patchy deposition. Varying the number of bilayers allows both sheet resistance and optical transparency to be tailored over a broad range. Carbon black-filled thin films able to achieve these levels of resistivity and transparency may find application in a variety of optoelectronic applications.     

New main chain nonlinear optical polymers with high glass transition temperatures

Summary Various 4-methoxy-4-carbomethoxy--amino--cyanostilbenes were prepared as mixtures of E and Z isomers, and polymerized via condensation polymerization using dibutyltin diacetate as catalyst. The resulting low molecular weight homopolymers showed higher glass transition temperatures (168–183°C) than previously reported main chain nonlinear optical (NLO) homopolymers. A high molecular weight (M_n30, 200) copolymer possessed an even higher glass transition temperature of 187°C. The hyperpolarizability of the polymers and a model compound were found by EFISH measurements to be in the range of 61 to 79x10^-48 esu.     

Enhanced efficiency of white polymer light-emitting diodes with inorganic nanodots

Enhanced efficiency of white polymer light-emitting diodes (PLEDs) was observed by incorporating polysilicic acid (PSA) nanodots into the hole-injection layer (HIL). The PLEDs employed three different phosphorescent dyes in a single emissive layer with a host polymer of poly(vinylcarbazole) (PVK). The optimal composition of the phosphorescent dyes has been found to accomplish the white emission. By incorporating 1.5 wt% of PSA nanodots into the HIL, the maximum efficiency has been found to increase about 65%, from 13.7 cd/A to 22.9 cd/A. This remarkable improvement in efficiency may be attributed to the introduction of the PSA nanodots, which leads to the better carrier balance in the PLEDs.     

Fluorophosphate glasses doped with PbSe quantum dots and their nonlinear optical characteristics

A new fluorophosphate glass matrix containing PbSe quantum dots characterized by a narrow size distribution (ΔR/R ∼ 5–7%, where R is the size of a quantum dot) is prepared under heat treatment. It is demonstrated that fluorophosphate glasses can be doped by introducing (ZnSe + PbO) or PbSe into the composition of the glass. The optical absorption spectra of the quantum dots corresponding to the strong quantum confinement regime are studied over a wide range of quantum-dot sizes (4–18 nm). The nonlinear optical absorption is investigated at a wavelength of 1.54 μm. It is revealed that the introduction of (ZnSe + PbO) rather than of PbSe into the composition of the glass improves the bleaching contrast owing to a more uniform distribution of the quantum dots over the volume of the glass sample.     

Novel second-order nonlinear optical main-chain polyurethanes: Adjustable subtle structure, improved thermal stability and enhanced nonlinear optical property

A series of main-chain polyurethanes containing sulfonyl-based NLO chromophores in the polymer backbone were prepared, the subtle structure of the chromophore moieties could be easily modified to adjust the property of the resultant polymers. The polymers exhibit improved stability of their enhanced NLO effects, besides their good processability, thermal stability, and relatively good transparency. The tested NLO properties of the polymers demonstrate that there is a suitable isolation group present for the sulfonyl-based chromophore to boost its microscopic β value to possibly higher macroscopic NLO property efficiently, and BOP moieties are the best choice for this series of polymers to achieve optimized properties.     

芳香族偶氮化合物三阶非线性光学材料的合成研究

将含有不同取代基的芳胺在0~5℃下与亚硝酸钠和盐酸进行重氮化反应(摩尔比为芳胺∶亚硝酸钠=1∶1.2),制得相应的重氮盐,再分别与苯代三聚氰胺(BGA)(摩尔比为芳胺∶苯代三聚氰胺=1∶0.8)发生偶合反应,最终得到一系列新的含有不同取代基的芳香族偶氮化合物,反应收率为57%~65%。通过红外、紫外、元素分析、核磁对其结构进行了表征。     

Chromophore-functionalised polymides with high-poling stabilities of the nonlinear optical effect at elevated temperature

Functionalised second-order nonlinear optical (NLO) polyimides have been developed. The key challenge in our approach was a one-step synthesis of these polymers, by reaction of di(hydroxyalkyl) chromophores and diimides utilising the Mitsunobu reaction. Glass transition temperatures in the range of 205-224°C were obtained. Thin spincoated films of the polymers were corona-poled and analysed by second-harmonic generation; values for d₃₃ of 30 pm/V were obtained. Poled order stability measurements over periods of 210-500 h resulted in 70-90% of remaining NLO-response at 125°C.     

Thermal and pH dual stimuli-responsive hybrid inclusion complex with tunable nonlinear optical properties

A novel dual-responsive core-shell type hybrid inclusion complex composed of an azobenzene-terminated copolymer PNIPAM-b-PAA and β-cyclodextrin-modified silver/polydiacetylene (β-CD@Ag/PDA) nanocrystals had been fabricated based on the host-guest interaction between azobenzene unit in the block copolymer and β-CD cavities on the surface of the hybrid nanocrystals. While the hybrid nanocrystals provide necessary nonlinear optical properties, the copolymer shells exhibit dual sensitivity to temperature and pH variation. The dual stimuli-responsive behavior of the copolymer shells was used to act as the driving force to adjust the relative spatial distances between neighboring hybrid nanocrystals, further controlling the localized surface plasmon resonance enhancement and the corresponding NLO effect. It is expected that this research will introduce a new way for preparing novel smart NLO materials.