Dendritic Phenylazomethine Research Articles

Poly-phenylene jacketed tailor-made dendritic phenylazomethine ligand for nanoparticle synthesis.

Synthesizing metal clusters with a specific number of atoms on a preparative scale for studying advanced properties is still a challenge. The dendrimer templated method is powerful for synthesizing size or atomicity controlled nanoparticles. However, not all atomicity is accessible with conventional dendrimers. A new tailor-made phenylazomethine dendrimer (DPA) with a limited number of coordination sites (n = 16) and a non-coordinating large poly-phenylene shell was designed to tackle this problem. The asymmetric dendron and adamantane core four substituted dendrimer (PPDPA16) were successfully synthesized. The coordination behavior confirmed the accumulation of 16 metal Lewis acids (RhCl3, RuCl3, and SnBr2) to PPDPA16. After the reduction of the complex, low valent metal nanoparticles with controlled size were obtained. The tailor-made dendrimer is a promising approach to synthesize a variety of metal clusters with desired atomicity.

Low-Temperature H2 Reduction of Copper Oxide Subnanoparticles.

Subnanoparticles (SNPs) with sizes of approximately 1 nm are attractive for enhancing the catalytic performance of transition metals and their oxides. Such SNPs are of particular interest as redox-active catalysts in selective oxidation reactions. However, the electronic states and oxophilicity of copper oxide SNPs are still a subject of debate in terms of their redox properties during oxidation reactions for hydrocarbons. In this work, in situ X-ray absorption fine structure (XAFS) measurements of Cu28 Ox SNPs, which were prepared by using a dendritic phenylazomethine template, during temperature-programmed reduction (TPR) with H2 achieved lowering of the temperature (T50 =138 °C) reported thus far for the CuII →CuI reduction reaction because of Cu-O bond elongation in the ultrasmall copper oxide particles.

Size-Dependent Oxidation State and CO Oxidation Activity of Tin Oxide Clusters

The CO oxidation reaction is an industrially important reaction; however, the practical catalysts are limited to noble metals. In this paper, we report a systematic study of the CO oxidation ability on cheap and less noble tin oxide clusters with the aim of quantitatively understanding the active sites. We synthesized size-controlled tin oxide clusters in mesoporous silica using the dendrimer templating method, employing dendritic phenylazomethine with a tetraphenylmethane core (TPMG4) as the template molecule. The clusters had different sizes depending on the added amount of SnCl2 as a precursor to TPMG4. The synthesized tin oxide clusters contained not only stable tetravalent Sn(IV) but also metastable divalent Sn(II) due to the structural stability and had a size-dependent composition. The CO oxidation activity of the tin oxide clusters increased with decreasing cluster size depending on the Sn(II)/Sn(IV) ratio. We also found the correlation between the Sn(II) fraction and the CO oxidation activity, cl...

Charge Transport in Dendrimer Melts Using Multiscale Modeling Simulation.

In this article, we present a theoretical calculation of the charge carrier mobility in two different dendrimeric melt systems (dendritic phenylazomethine with a triphenyl amine core and dendritic carbazole with cyclic phenylazomethine as the core), which have recently been reported1 to increase the efficiency of dye-sensitized solar cells by interface modification. Our mobility calculation, which is a combination of molecular dynamics simulation, first-principles calculation, and kinetic Monte Carlo simulation, leads to mobilities that are in quantitative agreement with available experimental data. We also show how the mobility depends on dendrimer generation. Furthermore, we examine the variation of mobility with an external electric field and external reorganization energy. Physical mechanisms behind the observed electric field and generation dependencies of mobility are also explored.

Macromolecular semi-rigid nanocavities for cooperative recognition of specific large molecular shapes

Molecular shape recognition for larger guest molecules (typically over 1 nm) is a difficult task because it requires cooperativity within a wide three-dimensional nanospace coincidentally probing every molecular aspect (size, outline shape, flexibility and specific groups). Although the intelligent functions of proteins have fascinated many researchers, the reproduction by artificial molecules remains a significant challenge. Here we report the construction of large, well-defined cavities in macromolecular hosts. Through the use of semi-rigid dendritic phenylazomethine backbones, even subtle differences in the shapes of large guest molecules (up to ~2 nm) may be discriminated by the cooperative mechanism. A conformationally fixed complex with the best-fitting guest is supported by a three-dimensional model based on a molecular simulation. Interestingly, the simulated cavity structure also predicts catalytic selectivity by a ruthenium porphyrin centre, demonstrating the high shape persistence and wide applicability of the cavity.

Enhancing the Photoelectric Effect with a Potential-Programmed Molecular Rectifier

Dendrimer-based electron rectifiers were applied to photoconducting devices. A remarkable enhancement of the photocurrent response was observed when a zinc porphyrin as the photosensitizer was embedded in the dendritic phenylazomethine (DPA) architecture. The dendrimer-based sensitizer exhibited a 20-fold higher current response than the non-dendritic zinc porphyrin. In sharp contrast, a similar application of the dendrimer with poly(vinylcarbazole) as the electron donor resulted in a decreased response. This is consistent with the idea that the DPA facilitates electron transfer from the core to its periphery along a potential gradient, as predicted by density functional theory calculations.

Copper‐containing bimetallic complexes as efficient catalysts for aerobic oxidative coupling polymerization

The aerobic oxidative polymerization of 2,6‐difluorophenol (F2PhOH) catalyzed by copper(II) for assembling dendritic ligands was studied. Although the mono‐metallic complex of copper(II) chloride with a dendritic phenylazomethine (DPAG4) efficiently catalyzed this polymerization reaction without any additive bases, a significant increase in the molecular weight of the product polymer was observed when an iron(III) complex was added to the copper(II)–dendrimer system. The synergistic enhancement based on the copper–iron bimetallic system provided a higher molecular weight product polymer in addition to the high yield. Copyright © 2011 John Wiley & Sons, Ltd.

Stepwise Radial Complexation of Organic Molecules and Organic–Metal Hybrid Assembly in Dendritic Polyphenylazomethines

Abstract We found that triphenylmethylium tetrafluoroborate (TPM+BF4−) could be coordinated to the imine group of dendritic phenylazomethine (DPA) in stepwise radial fashion, which allows for control of the number and position of TPM and metals incorporated into the dendrimers. Organic–metal hybrid assembly was also achieved.

Precise Assembly of Photo-functional Molecules in Phenylazomethine Dendrimer

Precise assembly of photo-functional molecules on dendritic phenylazomethine (DPA) was demonstrated. We previously reported the precise assembly of metal ions on dendritic phenylazomethine in stepwise radical fashion. Triphenylmethylium tetrafluoroborate (TPMBF4) could be coordinated to the imine group of DPA, which allows for control of the number and position of organic molecules in DPA. As one of the applications of an organic molecular assembly, TPM+ derivatives holding a photo-functional molecule, azobenzene (Azo-TPM), were incorporated into DPA stepwisely.

Long-Lived Hole Stabilized at a Triphenylamine Core and Shielded by Rigid Phenylazomethine Dendrons: A Pulse Radiolysis Study

The optical properties and reactivity of one-electron oxidized states (radical cations) of dendrimers are investigated in benzonitrile solutions by nanosecond pulse radiolysis. The hole stabilized at the triphenylamine (TPA) core is effectively shielded by a rigid dendritic phenylazomethine (DPA) shell of four generations, leading to an extension of its lifetime by nearly 2 orders of magnitude in comparison with a core radical cation without dendrons. A continuous red shift of the peak in the photoabsorption spectrum in the visible region and a decrease in the extinction coefficients (oscillator strengths) are found with increasing dendrimer generation number. These experimental observations are compared to the results of time-dependent density functional theory. It is suggested that bulky, rigid, insulating DPA dendrons shield against outer reactants and stabilize hole at the TPA core. Correlating the dendrimer generation number with the optical properties and reactivities of the radical cations could shed light on fundamental aspects of structurally defined nanoenvironments having hyperbranched entities.

Additive-Free Synthesis of Poly(phenylene oxide): Aerobic Oxidative Polymerization in a Base-Condensed Dendrimer Capsule

The additive-free synthesis of poly(phenylene oxides) by aerobic oxidation was achieved using a copper complex in a dendritic phenylazomethine structure. The outer shell composed of Schiff base units assists the catalytic function of the inner Cu complex moiety. It is important that the hybrid structure should be designed with a rigid architecture not to deactivate the catalytic center. Due to the rigid π-conjugating structure of the phenylazomethine dendrimer, the metal center can retain its fine conformation. This catalyst drastically decreased the total waste required to produce the PPO derivatives and provided a new approach to green polymerization.

Catalytic dehalogenation enhanced by appending dendritic ligands on cobalt porphyrins

The dehalogenation activities of cobalt porphyrin catalysts with dendritic phenylazomethine units on the meso-positions were studied. Tetrachloroethylene was used as a substrate. By applying samarium iodide as a reducing agent, the tetrachloroethylene conversion into trichloroethylene and dichloroethylene was observed in the presence of the cobalt porphyrin catalyst. The turnover frequency was 1.70 min−1 when a cobalt porphyrin connected with dendritic phenylazomethines (3 generations) was employed as the catalyst. While the turnover frequency was almost the same as that for a non-dendritic porphyrin catalyst (1.57 min−1 by cobalt tetraphenylporphyrin), a significant increase in the turnover frequency was observed when samarium (3.43 min−1) or terbium trifluoromethane sulfonate (8.57 min−1) binds to the phenylazomethine units of the dendrimer. Because these metal ions ( Sm 3+ or Tb 3+) are positioned in a space between the encapsulated catalytic center and the solvent phase, they can act as electron mediators that relay electrons from the reducing agent (samarium iodide) to the catalytic center (cobalt porphyrin). This facile electron transfer would provide an enhancement in the catalytic activity for the tetrachloroethylene reduction leading to dehalogenation.

Novel Functional Groups with Fine-Controlled Metal Assembling Function

Abstract Half-substituted dendritic phenylazomethine dendrimers with various substituents (Half-DPA-X Gn, where n is the generation number) were synthesized in order to elucidate the electron gradients in the dendrons by complexation with metal ions. Along with the change in the UV–vis spectra, the isosbestic point shifted about 11 nm from 371 to 360 nm. The number of added equivalents of SnCl2 required to induce a shift was in agreement with the number of the imine sites present in each layer of Half-DPA-H G4. The degree of the electron gradient in the phenylazomethine monodendrons, Half-DPAs, was estimated via titration with trifluoroacetic acid. We found drastic differences in the basicity of the imine sites; the basicity of the core imines is higher than that of the more peripheral imines. The stepwise complexation behavior is thermodynamically controlled from the core to terminal imines in Half-DPA-H. Furthermore, Half-DPA G4 with various substituents possesses the same electron gradients in the dendron, so the complexation behavior with metal ions is the same.

Synthesis and Electroluminescence Properties of Novel Main Chain Poly(p-phenylenevinylene)s Possessing Pendant Phenylazomethine Dendrons as Metal Ligation Sites

Novel poly(p-phenylenevinylene)s with a dendritic phenylazomethine (DPA-PPVs) were synthesized via the Heck reaction by initially complexing with rare-earth-metal ions, by filling up the coordination trap site of dendritic phenylazomethine (DPA) as the catalyst. The physical properties of the DPA-PPVs were evaluated. The solution, thermal, and optical properties affected by the various contents and generation of the DPA were investigated. DPA-PPV with the lower content and a smaller generation number showed the longest absorption and fluorescence maximum wavelength based on a relatively planar structure and a longer conjugation length. These polymers successfully assemble metal ions on their imine site supported by the spectral change similar to their monomeric model compounds. Two types of electroluminescent (EL) devices were fabricated: (I) ITO/PEDOT/DPA-PPV/Alq/CsF/Al; (II) ITO/PEDOT/DPA-PPV/TAZ/Alq/CsF/Al, where Alq (tris-8-hydroxyquinoline aluminum) acts as an electron transport layer (ETL) and TAZ ...

Novel poly(p-phenylenevinylene)s with a phenylazomethine dendron as a metal-collecting site.

Novel poly(p-phenylenevinylene)s (PPVs) with a dendritic phenylazomethine (DPA) as a metal-collecting site were synthesized via the Heck reaction by filling the coordination site of DPA moiety via complexation with rare earth metal ions.