Phenylazomethine Dendrimers Research Articles

(Invited) Synthesis of Multi-Metallic Nanoparticles for Advanced Catalysts

Dendrimers are highly branched organic macromolecules with successive layers or “generations” of branch units surrounding a central core. Organic inorganic hybrid versions have also been produced, by trapping metal ions or metal clusters within the voids of the dendrimers. Their unusual, tree-like topology endows these nanometer-sized macromolecules with a gradient in branch density from the interior to the exterior, which can be exploited to direct the transfer of charge and energy from the dendrimer periphery to its core.We show that PtCl4, SnCl2, FeCl3, and so on complexes to the imines groups of a spherical polyphenylazomethine dendrimer in a stepwise fashion according to an electron gradient, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. By attaching an electron-withdrawing group to the dendrimer core, we are able to change the complexation pattern, so that the core imines are complexed last. By further extending this strategy, it should be possible to control the number and location of metal ions incorporated into dendrimer structures, which might and uses as tailored catalysts, building blocks, or fine-controlled clusters for advanced materials. The metal-assembly in a discrete dendrimer molecule can be converted to a size-regulated metal particle with a size smaller than 1 nm as a molecular reactor. Due to the well-defined number of metal clusters in the subnanometer region, its property is much different from that of bulk or general metal nanoparticles. The chemistry of nanocatalysts on the sub-nanometer scale is not yet well understood because precise multi-metallic nanoparticles are difficult to synthesize with control over size and composition. The template synthesis of multi-metallic sub-nanocalaysts is achieved using a phenylazomethine dendrimer as a macromolecular template.

(Invited) Synthesis of Multi-Metallic Nanocatalysts Using a Dendrimer Reactor

Dendrimers are highly branched organic macromolecules with successive layers or “generations” of branch units surrounding a central core. Organic inorganic hybrid versions have also been produced, by trapping metal ions or metal clusters within the voids of the dendrimers. Their unusual, tree-like topology endows these nanometer-sized macromolecules with a gradient in branch density from the interior to the exterior, which can be exploited to direct the transfer of charge and energy from the dendrimer periphery to its core.We show that AuCl3, SnCl2, FeCl3, and so on complexes to the imines groups of a spherical polyphenylazomethine dendrimer in a stepwise fashion according to an electron gradient, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. By attaching an electron-withdrawing group to the dendrimer core, we are able to change the complexation pattern, so that the core imines are complexed last. By further extending this strategy, it should be possible to control the number and location of metal ions incorporated into dendrimer structures, which might and uses as tailored catalysts, building blocks, or fine-controlled clusters for advanced materials. The metal-assembly in a discrete dendrimer molecule can be converted to a size-regulated metal particle with a size smaller than 1 nm as a molecular reactor(Fig.). Due to the well-defined number of metal clusters in the subnanometer region, its property is much different from that of bulk or general metal nanoparticles. The chemistry of nanocatalysts on the sub-nanometer scale is not yet well understood because precise multi-metallic nanoparticles are difficult to synthesize with control over size and composition. The template synthesis of multi-metallic sub-nanocalaysts is achieved using a phenylazomethine dendrimer as a macromolecular template. Figure 1

(Invited, Digital Presentation) Synthesis of Multi-Metallic Clusters Using a Dendrimer Reactor

Dendrimers are highly branched organic macromolecules with successive layers or “generations” of branch units surrounding a central core. Organic inorganic hybrid versions have also been produced, by trapping metal ions or metal clusters within the voids of the dendrimers. Their unusual, tree-like topology endows these nanometer-sized macromolecules with a gradient in branch density from the interior to the exterior, which can be exploited to direct the transfer of charge and energy from the dendrimer periphery to its core.We show that tinchloride, SnCl2 and FeCl3 complexes to the imines groups of a spherical polyphenylazomethine dendrimer in a stepwise fashion according to an electron gradient, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. By attaching an electron-withdrawing group to the dendrimer core, we are able to change the complexation pattern, so that the core imines are complexed last. By further extending this strategy, it should be possible to control the number and location of metal ions incorporated into dendrimer structures, which might and uses as tailored catalysts, building blocks, or fine-controlled clusters for advanced materials. The metal-assembly in a discrete molecule can be converted to a size-regulated metal particle with a size smaller than 1 nm as a molecular reactor. Due to the well-defined number of metal clusters in the subnanometer size region, its property is much different from that of bulk or general metal nanoparticles. The chemistry of metal clusters on the sub-nanometer scale is not yet well understood because metal clusters, especially multi-metallic clusters, are difficult to synthesize with control over size and composition. The template synthesis of multi-metallic sub-nanoclusters is achieved using a phenylazomethine dendrimer as a macromolecular template.

Controlled Synthesis of Au25 Superatom Using a Dendrimer Template.

Superatoms are promising materials for their potential in elemental substitution and as new building blocks. Thus far, various synthesis methods of thiol-protected Au clusters including an Au25 superatom have been investigated. However, previously reported methods were mainly depending on the thermodynamic stability of the aimed clusters. In this report, a synthesis method for thiol-protected Au clusters using a dendrimers template is proposed. In this method, the number of Au atoms was controlled by the stepwise complexation feature of a phenylazomethine dendrimer. Therefore, synthesis speed was increased compared with the case without the dendrimer template. Hybridization for the Au25 superatoms was also achieved using the complexation control of metals.

Dendrimer-encapsulated PtSn bimetallic ultrafine nanoparticles supported on graphitic mesoporous carbon as efficient electrocatalysts for methanol oxidation

Catalytic performance of Pt based nanocatalysts significantly depends on their morphologies, compositions and structures. In this work, the generation-4 phenylazomethine-tetraphenylmethane dendrimer (TPMG4)-encapsulated PtSn bimetallic ultrafine nanoparticles with tunable ratio of Pt and Sn (PtnSn60-n@TPMG4/GMC, n = 56, 48, 32) supported on graphitic mesoporous carbon (GMC) were fabricated through co-reduction method by using the phenylazomethine dendrimer as a template. The morphologies, compositions, and structures of resulting PtnSn60-n@TPMG4/GMC were detected by UV–vis absorption spectra (UV–vis), inductively coupled plasma-optical emission spectroscopy (ICP-OES), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements. These physical characterizations show that dendrimer-encapsulated PtnSn60-n nanoparticles are anchored on the surface of graphitic mesoporous carbon with highly dispersion and uniformly ultrafine size of ∼1 nm, The atomic ratio of Pt and Sn in PtnSn60-n bimetallic nanoparticles can be accurately controlled. The electrochemical characterizations demonstrate that all PtnSn60-n@TPMG4/GMC samples exhibit more excellent electrocatalytic performance for methanol oxidation than single metal Ptm@TPMG4/GMC and commercial carbon supported platinum catalyst (Pt/C). Especially, the Pt56Sn4@TPMG4/GMC displays the highest catalytic activity with 1.6 times higher than Pt60/GMC and 1.9 times higher than Pt/C. Also, the Pt56Sn4@TPMG4/GMC exhibits the high carbon monoxide (CO) tolerance and superior catalytic stability towards methanol oxidation. Consequently, constructing Pt based bimetallic nanoparticles with controllable compositions and structures is an effective way to improve the catalytic performance and reduce the amount of Pt used in the catalysts, which will be widely concerned in the field of direct methanol fuel cells.

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.

Functionalization of phenylazomethine dendrimers

Functionalization of phenylazomethine dendrimers

Expansion of Dendrimer Template Function for Subnanoparticle Synthesis

Unusual complex formation of PtBr4 in THF was investigated for phenylazomethine dendrimer templates. The characteristics made it possible to reverse-order assemble platinum salts by changing the solvent composition of the dendrimers. This reverse-order assembly method enabled full-range tuning of metal ratios for hybridization, which was inherently difficult for templates with a typical dendritic structure.

Electrochemical Measurement of Bismuth Clusters in Dendrimer Through Transformation from Atomicity Controlled Complexes

Dendrimers can provide unique reaction space for sub-nano sized materials. Recently, we have demonstrated a luminous bismuth dendrimer and the on/off switching by stepwisely assembled bismuth units in a phenylazomethine dendrimers. In addition, formation of bismuth clusters was also demonstrated by the reduction of the bismuth salts assembled in the dendrimer. In this study, we have revealed the atomicity dependency about the reduction and oxidation potentials of the assembled bismuth complexes and clusters, respectively. The measurements were conducted by the electrochemical process of the bismuth assembled dendritic poly-phenylazomethines.

Atom-hybridization for synthesis of polymetallic clusters

The chemistry of metal clusters on the sub-nanometer scale is not yet well understood because metal clusters, especially multimetallic clusters, are difficult to synthesize with control over size and composition. The template synthesis of multimetallic sub-nanoclusters is achieved using a phenylazomethine dendrimer as a macromolecular template. Its intramolecular potential gradient allows the precise uptake of metal precursor complexes containing up to eight elements on the template. The usefulness of this method is demonstrated by synthesizing multimetallic sub-nanoclusters composed of five elements (Ga1In1Au3Bi2Sn6). The size and composition of this cluster can be precisely controlled and the metals involved are alloyed with each other. This approach provides the ability to easily blend different metals in various combinations to create new materials on the sub-nanometer scale, which will lead to the development of a new area in the field of chemistry.

Build-up enhancement of photoluminescence from phenylazomethine bismuth dendrimer using Bi(OTf)3

Metal assembly to a dendrimer can provide various functionalities based on the branched structure. Here, we researched assembly phenomena of bismuth salts in the phenylazomethine dendrimer and achieved enhancement of emission intensity per metal unit by using Bi(OTf)3. This enhancement suggested increasing of Bi–N coordination bonds derived from the bismuth units in the dendrimer.

Insight into the Effect of Dendrimer Structure on Photoluminescence from Assembled Bismuth Complexes

Our previous report demonstrated the fabrication and functionalization of the luminous dendrimer based on phenylazomethine-BiCl3 complexes (Kambe et al. in Angew Chem Int Ed 55:13151, 2016). It is now revealed that the bismuth assembled phenylazomethine dendrimers have different luminous efficiencies depending on the layers of the DPAG4 by photoemission and absorption spectroscopy.

Polymerization of a divalent/tetravalent metal-storing atom-mimicking dendrimer.

The phenylazomethine dendrimer (DPA) has a layer-by-layer electron density gradient that is an analog of the Bohr atom (atom mimicry). In combination with electron pair mimicry, the polymerization of this atom-mimicking dendrimer was achieved. The valency of the mimicked atom was controlled by changing the chemical structure of the dendrimer. By mimicking a divalent atom, a one-dimensional (1D) polymer was obtained, and by using a planar tetravalent atom mimic, a 2D polymer was obtained. These poly(dendrimer) polymers could store Lewis acids (SnCl2) in their unoccupied orbitals, thus indicating that these poly(dendrimer) polymers consist of a series of nanocontainers.

Bismuth Complexes in Phenylazomethine Dendrimers: Controllable Luminescence and Emission in the Solid State

Dendritic phosphors were obtained by the stepwise integration of BiCl3 in phenylazomethine dendrimers. The bismuth-coordinated phenylazomethines displayed photoluminescence at 500-800 nm, and the intensity could be tuned by changing the stoichiometry of BiCl3 and the dendrimer. This phosphor did not show serious luminescence quenching even though the local concentration of BiCl3 in the dendrimer was as high as 20 M, and luminescence was also observed in the solid state. The absorption and emission properties could be reversibly switched by addition of a Lewis base or under electrochemical redox control, which induced the reversible complexation of BiCl3 in the dendrimer.

Bismuth Complexes in Phenylazomethine Dendrimers: Controllable Luminescence and Emission in the Solid State

AbstractDendritic phosphors were obtained by the stepwise integration of BiCl3 in phenylazomethine dendrimers. The bismuth‐coordinated phenylazomethines displayed photoluminescence at 500–800 nm, and the intensity could be tuned by changing the stoichiometry of BiCl3 and the dendrimer. This phosphor did not show serious luminescence quenching even though the local concentration of BiCl3 in the dendrimer was as high as 20 M, and luminescence was also observed in the solid state. The absorption and emission properties could be reversibly switched by addition of a Lewis base or under electrochemical redox control, which induced the reversible complexation of BiCl3 in the dendrimer.

(Invited) Metal Assembly of a Dendrimer with a Porphyrin Core

Dendrimers are highly branched organic macromolecules with successive layers or “generations” of branch units surrounding a central core. Organic inorganic hybrid versions have also been produced, by trapping metal ions or metal clusters within the voids of the dendrimers. Their unusual, tree-like topology endows these nanometre-sized macromolecules with a gradient in branch density from the interior to the exterior. Here we show that tin ions, SnCl2 and FeCl3complexes to the imines groups of a spherical polyphenyl-azomethine dendrimer in a stepwise fashion according to an electron gradient, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. Many metal halides can be assembled inside the phenylazomethine dendrimer with a Zn-porphyrin core(DPA-ZnP) by the strong coordination ability of the imines in DPAs. The 60 equivalents of SnCl2 should be included in the fourth generation DPA-ZnP (DPAG4-ZnP), which has 60 imine sites, because SnCl2 is complexed with an imine at the ratio of 1:1. Complexation of DPA G4-ZnP with SnCl2 was confirmed as a shift in the absorption based on p-p* transition of imines in the UV-vis spectra. During the complexation of DPA G4-ZnP with SnCl2, four shifts in the isosbestic point were observed in the spectra. If SnCl2 molecules are complexed with the imines in DPAs at random, the isosbestic point is not shifted during the titration of SnCl2. However, the isosbestic point was observed at 370, 368, 366, and 362 nm during the addition of 0-4, 5-12, 13-28, and 29-60 equivalents of SnCl2 to the dichloromethane/ acetonitrile solution of DPA G4-ZnP, respectively. These shifts show that the complexation proceeds in four steps. The amounts of the added SnCl2 in each step, i.e., 4, 8, 16, and 32 equivalents, agree with the number of imines in the 1st to 4th shells. This result shows that SnCl2 molecules are assembled from the core to the terminals of DPA G4-ZnP in a stepwise fashion. This radial stepwise complexation was also observed for the other dendrimers with phenylazomethine dendron skeletons. This complexation behavior means that the number and the position of the metal ions in the dendrimers are controllable.

Effect of the Core Structure on the Sequential Coordination of Phenylazomethine Dendrimer

Phenylazomethine dendrimer (DPA) is a dendritic ligand that coordinates to various Lewis acids in a stepwise radial fashion. Second generation para-substituted and meta-substituted phenylazomethine dendrimers with p-phenylenediamine and m-phenylenediamine core were synthesized and the coordination sequence was investigated by UV–vis titration. Stepwise radial complexation from the outer layer was observed for the m-phenylenediamine core meta-substituted phenylazomethine dendrimer (m-mG2). Other three dendrimers showed stepwise radial complexation from the inner layer. The reason could be explained with the binding constant of the 1st generation dendrimer (model of the 1st layer). This is suggesting that for controlling the coordination sequence of DPA, not only the dendron structure is important, but also the structure of the core is an important factor.

Synthesis and Properties of Nitrogen-Introduced Phenylazomethine Dendrimer

The pyridine ring–introduced phenylazomethine dendrimer (PyDPA) was synthesized by a dehydration reaction using titanium(IV) chloride. The ultraviolet–visible absorption and the electrochemical study showed that the introduction of the pyridine ring produces a smaller band gap by increasing the highest occupied molecular orbital level and decreasing the lowest unoccupied molecular orbital level. A crystal of a PyDPA-PdCl2 complex was also prepared. Traditional phenylazomethine dendrimers cannot form a complex with palladium, indicating that PyDPA can potentially coordinate with various metal salts such as Co, Ni, Ru, and Mn and can be used for catalytic or electronic applications.

Stepwise radial complexation from the outer layer to the inner layer of a dendritic ligand: a phenylazomethine dendrimer with an inverted coordination sequence.

A para-substituted phenylazomethine dendrimer (pGnA) coordinates to Lewis acids in a stepwise radial fashion from the inner layer to the outer layer. The inversion of this coordination sequence was achieved for the first time by just changing the substitution position of the phenylazomethine group from the para position to the meta position (mGnA).

Deposition of gallium oxide nanodots prepared from metal-assembling dendrimer molecules isolated by the spacing of the nonmetal-assembling dendrimer molecules in the two-dendrimers mixture monolayer

Phenylazomethine dendrimers (DPA) can precisely incorporate metal chlorides onto the imine sites in a stepwise fashion. Such precise dendrimer–metal complexes allow the preparation of size-controlled subnanometer metal particles. We now propose a novel approach for the fabrication of size-controlled subnanometer metal oxide dots isolated on a substrate using two different-type dendrimers. One is a fourth-generation phenylazomethine dendrimer (DPAG4) and the other is a benzylether dendrimer (BzEG3) with a zinc porphyrin core. Even though the diameter of BzEG3 corresponds to that of DPAG4, BzEG3 has no metal-complexing site. Upon dip coating on a highly oriented pyrolytic graphite substrate by the mixed solution of the metal chloride-assembling DPAG4 molecules and BzEG3 molecules, the dendrimer monolayer was immobilized on the substrate. The concentration of the dendrimer mixture was determined in order to separate each DPAG4–metal chloride complex molecule by BzEG3. Monodispersed metaloxide nanodot arrays could be obtained from the dendrimer monolayer in which DPAG4–metal chloride complex molecule is well isolated by the BzEG3 as a spacer after the hydrolysis of metal chlorides followed by the complete removal of dendrimers. Copyright © 2013 John Wiley & Sons, Ltd.