Dendritic Polyphenylazomethines Research Articles

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.

Reducing Capsule Based on Electron Programming: Versatile Synthesizer for Size-Controlled Ultra-Small Metal Clusters.

Controlled reducing capsules with a specific number of reducing electrons were achieved by appropriately placed BH3 units in the dendritic polyphenylazomethines (DPAs). Using the 1:1 coordination fashion on their basic branches with radius affinity gradient, the 4th generation DPA (DPAG4) possessing four BH3 units in the central positions was prepared as a template synthesizer for size-controlled ultra-small metal clusters. This was well-demonstrated by reduction of Ag, Pt, and other metal ions resulting in monodispersed ultra-small clusters.

Control of Single Molecular Nanodot Patterns of Phenyl Azomethine Dendrimers by Statistical Simulation

Precisely synthesized subnanometer particles of metals or metal oxides can be prepared using dendritic polyphenyl azomethines as the template. With a goal of their arrays to a surface using a simple and quick process, such as spin-casting, statistical analyses were applied to a nanodot array of the dendrimers to obtain the relationship between the experimental condition and the results such as size, spacing, or its standard deviations. The dot patterns of a single molecular dendrimer on a substrate were able to be predicted with numerical values of the experimental parameters associated with the spin coat (concentration of the dendrimer, physical properties of solvent, the spin coating recipe, temperature of the solution, relative humidity (RH)) as the inputs for the statistical analysis.

Controlled Storage of Ferrocene Derivatives as Redox-Active Molecules in Dendrimers

Dendritic polyphenylazomethines (DPA) could encapsulate ferroceniums by complexation of the electron-donating skeleton of the DPA imines. Upon addition of ferroceniums to a series of dendritic polyphenylazomethines (DPAGX, where X is the generation number, X = 1-4), the UV-vis spectra showed changes in a manner similar to that observed for the complexation of metal ions with DPAGX. Stepwise shifts in the isosbestic point were consistently observed with the number of imine groups in the first and second layers of the generation-4 dendrimer (DPAG4). DPAG2 and DPAG3 were also found to trap 6 equiv of ferroceniums. To investigate the complexation, UV-vis spectroscopy, (57)Fe Mossbauer spectroscopy, electrospray ionization-mass spectroscopy (ESI-MS), cyclic voltammetry (CV), and fluorescence spectroscopy were performed. We confirmed that neutral ferrocenes cannot complex with the imine group while ferroceniums can. Utilizing the redox property of ferrocenes, we were able to electrochemically control the encapsulation and release of ferrocenes into the DPA in a manner similar to redox-responsive proteins such as ferritin. In addition to ferrocenes, oligoferrocenes could also be trapped in the DPA. The biferrocene cation(1+) was particularly suitable for electrochemical switching due to its stable mixed valence condition. The terferrocene dication(2+) encapsulated into DPAG4 could be fabricated into a thin film, which exhibited the near-infrared absorption of an intervalence charge-transfer (IV-CT) band, pointing the way toward the use of such systems in material science.

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.

Divergent Approach for Synthesis and Terminal Modifications of Dendritic Polyphenylazomethines

In the past, dendritic polyphenylazomethines (DPA) have been synthesized via the convergent method. However, the convergent method has problems such as difficult terminal-group modifications and an increased number of steps. Therefore, we synthesized the terminal-protected DPA to construct the dendritic structure via the divergent method. The combination of the convergent method and the divergent method easily achieved the rapid synthesis of a higher generation dendrimer. Furthermore, we succeeded in the synthesis of the water-soluble PEG-DPA via the divergent method using the ester-DPA.

Investigation of a Molecular Morphology Effect on Polyphenylazomethine Dendrimers; Physical Properties and Metal‐Assembling Processes

A series of novel dendritic polyphenylazomethines (DPA) with asymmetric morphologies was synthesized. Their physical properties, such as encapsulating effect, molecular dynamics, and metal assembly, are strongly dependent on the entire conformation of the molecules. The most important property is layer-by-layer metal assembly in the dendrimer structure from the core to the outside. Bis- and tris-substituted DPAs of the fourth generation also act as frameworks for stepwise assembly of a metal component (SnCl2), like the fully substituted symmetric DPA. However, extensive investigation of metal assembly in specific DPAs revealed that they do not follow the stepwise process. The molecular density calculated from the experimental hydrodynamic volume indicated that bis- and tris-substituted DPAs with asymmetric morphology still retain a free space similar to that of fully substituted symmetric DPA. The monosubstituted DPA, however, displayed a slightly higher density (smaller space) than the other DPAs. The experimental results suggest a bent conformation of the dendrimer in which the core moiety is folded into the dendron structure. In addition, the molecular dynamics were probed by means of the 1H NMR signals of the porphyrin core. It was demonstrated that the conformation is not fixed at room temperature in solvated DPAs, especially in monosubstituted DPA. A similar observation was for the smaller DPAs (third generations) with asymmetric morphologies. These dendrimers do not follow the stepwise complexation process. The structures of bis- and tris-substituted dendrimers which accurately follow the stepwise process are fixed. These observations provide a new insight into the finely controlled metal-assembly chemistry of dendritic macromolecules, and a rigid and fixed conformation is one of important factors for their unique properties.

Synthesis of DPA dendron encapsulated gold clusters with metal-assembling function

Gold clusters modified with first, second and third generation dendritic polyphenylazomethines (DPA) were synthesized by an exchanged reaction of corresponding DPA dendron thiols. Measurements by high performance perfect sizer (HPPS) and TEM reveal that their diameters increase with a change in the chain length of the modifying molecules from the first to third generation. These gold clusters with DPA dendrons exhibit coordination quantitatively to metal ions such as Fe3+,Sn2+, etc., because of their imine groups; this then resulted in self-aggregation to form a large sphere.

Fine-control of Metal Assembling in Dendritic Polyphenylazomethines

Dendritic polyphenylazomethines (DPAs) with a regularly branched structure and a single molecular weight were synthesized using the convergent method. DPA derivatives having tris(thienylphenyl)amine and tetraphenylporphyrin as the core (TPA-DPAs and Por-DPAs) and aniline-capped DPAs were obtained during the dehydration of the DPA dendrons with tris(4-aminothienylphenyl)amine, tetra(4-aminophenyl)porphyrin, and aniline, respectively. We exploited the more efficient synthetic method of DPAs, and successfully obtained the fifth generation of DPA (DPA G5). Stepwise radial complexation with SnCl2 in DPAs, TPA-DPAs, Por-DPAs, and aniline-capped DPAs, was found as stepwise shifts of the isosbestic point during the UV–vis spectroscopic observation. This complexation behavior was supported by the shell-selective reduction of the imines. Using the shell-selective reduction method and the terminal-modification method of the DPAs, the core and terminals of DPAs were functionalized by a ferrocene unit(s), respectively. FeCl3 molecules were also complexed with the imines of the DPAs in a stepwise fashion. Encapsulation/releasing of Fe ions in DPA was electrochemically controlled due to the different complexation ability of Fe(II) and Fe(III) ions with the imines. TPA-DPAs were applied as hole-transporting materials in EL devices. Their efficiency was found to be enhanced when complexing with SnCl2.

精密金属集積高分子材料の創製と応用

Dendritic polyphenylazomethines (DPAs) having a regularly branched structure and a single molecular weight were synthesized via dehydration of aromatic amines with aromatic ketones. We found stepwise radial complexation with SnCl2 in DPAs by spectroscopic observation as stepwise shifts of the isosbestic point, and further supported by means of NMR, TEM, and shell-selective reduction of imines. Functionalization of DPAs was achieved by exploiting the modification methods of the core and terminals. Encapsulation/releasing of iron ions in DPA was electrochemically controlled due to the different complexation ability of Fe (II) and Fe (III) ions with the imines. DPAs were also applied to hole transporting materials in EL devices and catalysts for reduction of carbon oxide, and their efficiency was enhanced by the complexation with SnCl2.

Control of stepwise radial complexation in dendritic polyphenylazomethines.

The fourth generation of a dendritic polyphenylazomethine (DPA G4) has 2, 4, 8, and 16 imine groups in the first, second, third, and fourth shells, respectively (total, 30 imine groups). DPA G4 can trap 30 equiv of SnCl(2) molecules, because the imine group is complexed with SnCl(2) at a ratio of 1:1. During addition of 30 equiv of SnCl(2) to DPA G4, four shifts in the isosbestic point were observed in the UV-vis spectra, and the amount of SnCl(2) added in each step is in agreement with the number of imine groups in each shell of DPA G4. This result shows that the complexation of the imine groups in DPA G4 with SnCl(2) occurs stepwise in the order of the first, second, third, and fourth shells. The unique stepwise complexation was also observed in DPA G2 and G3 as two and three shifts of the isosbestic point, respectively. The stepwise complexation was supported by TEM, NMR, and a novel shell-selective reduction (SSR) method for imines. An expansion in the molecular size of DPA G4 by the complexation was revealed by molecular modeling and TEM measurements. The stepwise complexation is caused by the different basicity of the imine groups between the shells, which was supported by the chemical shifts of the peaks attributed to the imine carbons in the (13)C NMR spectra. The gradients in the basicity were controlled by the introduction of electron-withdrawing or -releasing groups to the core of the dendrimers; the core imines were complexed last in DPAs having a 2,3,5,6-tetrafluoro or 2,5-dichlorophenyl core due to the low basicity of the core imines. The different complexation pattern was also clearly confirmed by the SSR method.

Novel Topological Polyphenylazomethines Having Controlled Metal‐Assembling Properties

AbstractFor Abstract see ChemInform Abstract in Full Text.

精密金属集積能を有するポリフェニルアゾメチン新ナノ構造体

Novel dendritic polyphenylazomethines (DPAs) were synthesized up to the fourth generation by the convergent method via dehydration of aromatic ketones with aromatic amines in the presence of titanium (IV) tetrachloride. DPAs show high thermal stability and high solubility unlike the con-ventional linear polyphenylazomethines. Novel cyclic phenylazomethine trimers (CPAs) were syn-thesized in a one-step dehydration of the 4-aminobenzophenone derivatives in the presence of TiCl4 or p-toluenesulfonic acid (PTS). When using TiCl4 as the dehydration agent, the introduction of bulky substituents as the α-position of the substrate enhanced the yields of the CPAs. On the other hand, PTS served as an effective catalyst for the synthesis of the phenyl-substituted CPA. Cyclization in hyperbranched polymer synthesis was first controlled on the basis of a steric effect using a Lewis acid with bulky ligands. A novel dendrimer with a cyclic structure was quantitatively obtained via controlled cyclization using a monomer with a bulky dendron.

First synthesis of phenylazomethine dendrimer ligands and structural studies.

Novel dendritic polyphenylazomethines (DPAs), which consist of a pi-conjugated backbone, were synthesized up to the fourth generation by the convergent method via dehydration of aromatic ketones with aromatic amines in the presence of titanium(IV) tetrachloride. The obtained dendrimers, DPA G1-4 (designated as GX, where X is the generation number), show high thermostability (Td(10%) 521 degrees C in DPA G4) and high solubility for the common solvents such as chloroform, THF, and DMSO unlike the conventional linear polyphenylazomethines, which have very low solubilities. The DPA G4 molecule was confirmed to have a spherelike structure by GPC measurement and a molecular model based on the crystal structure of DPA G2. Crystal data for DPA G2: monoclinic space group P2(1)/a, a = 25.352(4) A, b = 8.577(2) A, c = 16.151(2) A, beta = 106.25(1) degrees, V = 3371.6(10) A(3), Z = 2, D(calc) = 1.168 g/cm(3), mu(Cu Kalpha) = 0.536 cm(-1), final R = 0.089, and R(w) = 0.287. The molecular modeling reveals that a DPA G4 molecule has a spherelike structure, in which the height, width, and depth are 2.3, 2.9, and 2.5 nm, respectively. The TEM and AFM pictures show the DPA G4 molecules to have a spherelike structure (the diameter: 2.3 nm) and are regularly assembled on a plate by casting. The occupied area of one DPA G4 molecule in a monolayer on water was estimated by pi-A measurements to be 3.8-4.2 nm(2) (the calculated diameter 2.2-2.3 nm, which agreed with the TEM result). NMR studies (1H NMR at 130 degrees C and T(1) measurements) supported a conformational rigidity of DPA G4 in solution.

Novel phenylazomethine dendrimers: synthesis and structural properties

The novel dendrimers consisting of a pi-conjugated backbone, the dendritic polyphenylazomethines (DPAs), were synthesized by the convergent method via the dehydration of aromatic ketones with aromatic amines in the presence of titanium(IV) tetrachloride. The obtained DPAs have a high solubility unlike the conventional linear polyphenylazomethines. NMR studies revealed the conformational rigidity of DPA G4. DPAs having many azomethine groups as the coordination site for metal ions are expected to be novel ligands.