ナノ粒子合成のためのカスタムメイド樹状フェニルアゾメチン

K. Albrecht, M. Taguchi, T. Tsukamoto, T. Moriai, N. Yoshida, K. Yamamoto
Chem. Sci. 2022, 13, 5813-5817.

特定の原子数を持つ金属クラスターを準備規模で合成して高度な特性を研究することは依然として課題である。デンドリマーテンプレート法は、サイズや原子数を制御したナノ粒子を合成するための強力な方法であるが、従来のデンドリマーではすべての原子数にアクセスすることはできない。この問題に対処するために、限られた数の配位サイト（n = 16）と非配位性の大きなポリフェニレンシェルを持つ新しいカスタムメイドのフェニルアゾメチンデンドリマー（DPA）が設計された。非対称デンドロンとアダマンタンコアの四置換デンドリマー（PPDPA16）は、成功裏に合成された。配位挙動により、PPDPA16に16個の金属ルイス酸（RhCl3、RuCl3、およびSnBr2）が蓄積されることが確認された。複合体の還元後、制御されたサイズの低原子価金属ナノ粒子が得られた。このカスタムメイドのデンドリマーは、望ましい原子性を持つさまざまな金属クラスターを合成するための有望なアプローチである。

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.

多核金属錯体分子の金属原子をラベルとした立体構造解析

K. Takada, M. Morita, T. Imaoka, J. Kakinuma, K. Albrecht, K. Yamamoto
Sci. Adv. 2021, 7, eabd9887.

単一分子の顕微観察は化学の分野で急速に拡大しており、多数の分子を必要とする従来の特性評価技術とは異なる。このような単一分子顕微鏡の一つに高角環状暗視野走査透過電子顕微鏡（HAADF-STEM）があり、原子番号依存のコントラストのため、特に配位化合物に適している。しかし、これまでのところ、HAADF-STEMを用いた単一分子観察は単純な平面分子に限られていた。本研究では、Irを原子ラベルとして用いることで、非平面デンドロン化ポリ核Ir錯体のサブナノメートル分解能での直接構造解析を実証する。デンドリマー錯体への電子線量を減少させることが単一分子観察の鍵である。立体異性体のシミュレートされたSTEM画像との比較を行い、最も可能性の高い立体配座を決定する。我々の結果は、従来の方法では不可能であった配位高分子の構造解析を実現するための電子顕微鏡観察の可能性を拡大するものである。

Metal atom–guided conformational analysis of single polynuclear coordination molecules

Microscopic observation of single molecules is a rapidly expanding field in chemistry and differs from conventional characterization techniques that require a large number of molecules. One of such form of single-molecule microscopy is high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), which is especially suitable for coordination compounds because of its atomic number–dependent contrast. However, to date, single-molecule observations using HAADF-STEM has limited to simple planar molecules. In the present study, we demonstrate a direct structural investigation of nonplanar dendronized polynuclear Ir complexes with subnanometer resolution using Ir as an atomic label. Decreasing the electron dose to the dendrimer complexes is critical for the single-molecule observation. A comparison with simulated STEM images of conformational isomers is performed to determine the most plausible conformation. Our results enlarge the potential of electron microscopic observation to realize structural analysis of coordination macromolecules, which has been impossible with conventional methods.

二価/四価の金属を貯蔵する原子模倣デンドリマーの重合

K. Albrecht, Y. Hirabayashi, M. Otake, S. Mendori, Y. Tobari, Y. Azuma, Y. Majima, K. Yamamoto
Science Adv. 2016, 2, e1601414.

フェニルアゾメチンデンドリマー（DPA）は、ボーア原子のアナログである層ごとの電子密度勾配を持ち、原子模倣を実現している。この電子対模倣と組み合わせることで、原子模倣デンドリマーの重合が達成された。模倣する原子の原子価はデンドリマーの化学構造を変えることで制御された。二価原子を模倣することで一次元（1D）ポリマーが得られ、平面四価原子を模倣することで二次元（2D）ポリマーが得られた。これらのポリ（デンドリマー）ポリマーは、未占有軌道にルイス酸（SnCl2）を貯蔵できるため、これらのポリ（デンドリマー）ポリマーが一連のナノコンテナで構成されていることを示している。

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

T. Kambe, A. Watanabe, T. Imaoka, K. Yamamoto
Angew. Chem. Int. Ed. 2016, 55, 13151-13154.

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.

Carbazole Dendrimers as Solution-Processable Thermally Activated Delayed-Fluorescence Materials

K. Albrecht, K. Matsuoka, K. Fujita, K. Yamamoto
Angew. Chem. Int. Ed. 2015, 54, 5677-5682.

溶液塗布可能な遅延蛍光材料としてのカルバゾールデンドリマー

Recently, thermally activated delayed fluorescence (TADF) materials have received increasing attention as effective emitters for organic light-emitting diodes (OLEDs). However, most of them are usually employed as dopants in a host material. In this report, carbazole dendrimers with a triphenyl-s-triazine core are reported, which are the first solution-processable, non-doped, high-molecular-weight TADF materials. The dendrimers were obtained by a new and facile synthetic route using the tert-butyldimethylsilyl moiety as a protecting group. All dendrimers showed TADF in toluene. Measurements of the temperature-dependent luminescence lifetime revealed that spin-coated neat films also showed TADF with moderate quantum yields. OLED devices incorporating these dendrimers as spin-coated emitting layers gave external quantum efficiencies of up to a 3.4 %, which suggests that this device is harvesting triplet excitons. This result indicates that carbazole dendrimers with attached acceptors are potential TADF materials owing to their polarized electronic structure (with HOMO–LUMO separation).

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

T. Imaoka, Y. Kawana, T. Kurokawa, K. Yamamoto
Nature Commun. 2013, 4, 2581.

【協働的に大型分子の形状を認識する少しだけ硬い高分子精密ナノ空間】

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

T. Imaoka, H. Ueda, K. Yamamoto
J. Am. Chem. Soc. 2012, 134, 8412-8415.

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.

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

Y. Ochi, M. Suzuki, T. Imaoka, M. Murata, H. Nishihara, Y. Einaga, K. Yamamoto
J. Am. Chem. Soc. 2010, 132, 5061-5069.

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, 57Fe Mössbauer 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.

Dendritic Structure Having a Potential Gradient: New Synthesis and Properties of Carbazole Dendrimers

K. Albrecht, K. Yamamoto
J. Am. Chem. Soc. 2009, 131, 2244-2251.

Dendritic Structure Having a Potential Gradient: New Synthesis and Properties of Carbazole Dendrimers

A new synthetic route for carbazole dendrimers was discovered using the copper-catalyzed N-arylation reaction. This synthetic route allowed synthesizing the fourth generation carbazole dendrimer and several derivatives for the first time. The crystal structure, Mark−Houwink−Sakurada plots, and UV−vis and fluorescence studies showed that the dendritic carbazole backbone has a rigid and highly twisted structure. From the measurement of the redox potential of the ferrocene derivatives, the IR spectra of the benzophenone derivatives, and complexation behavior of the phenylazomethine derivatives, the inductive electron-withdrawing effect of the carbazole dendron was revealed. This suggested that the summation of this electron withdrawal from each layer may produce a potential gradient such that the outer layer is electron-rich and the inner layer is electron-poor in the carbazole dendron. By assignment of the 1H and 13C NMR spectra of the dendron, the existence of this kind of potential gradient was proved. Overall, these data show the π-polarization substituent effect of the carbazole unit, and their summation determines the potential gradient in the repeating dendritic structure of the carbazole dendrimer.

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

K. Yamamoto, Y. Kawana, M. Tsuji, M. Hayashi, T. Imaoka
J. Am. Chem. Soc. 2007, 129, 9248-9532.

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.

Probing Stepwise Complexation in Phenylazomethine Dendrimers by a Metallo-Porphyrin Core

T. Imaoka, R. Tanaka, S. Arimoto, M. Sakai, M. Fujii, K. Yamamoto
J. Am. Chem. Soc. 2005, 127, 13896-13905.

Probing Stepwise Complexation in Phenylazomethine Dendrimers by a Metallo-Porphyrin Core

A series of dendritic phenylazomethines (DPA), which have a meso-substituted zinc porphyrin core (DPAGX-ZnP, X = 1−4), were synthesized. Structural studies of these dendrimers were carried out using Tri-SEC (triple detection after size exclusion chromatography), intrinsic viscosity analysis, TEM (tunneling electron microscopy), and molecular modeling calculations by AM1. As a result, a sphere-like structure within a single-nanometer scale (Rh = 22 Å for DPAG4-ZnP) was observed. In addition, encapsulating effects by the DPA shell in the larger dendrimers were confirmed as fundamental properties, based on the UV−vis abosorption spectra, cyclic voltammograms, and 1H NMR spin−lattice relaxation times (T1). The DPAGX-ZnP acts as a multi-metal ion reservoir for SnCl2 and FeCl3. The generation-4 dendrimer (DPAG4-ZnP) can take up to 60 molar amounts of metal complexes around the porphyrin core. A quantitative study of the metal assembling reaction by UV−vis titration revealed stepwise layer-by-layer complexations from the inner imines nearest to the core to the surface. The redox behavior and fluorescence of the zinc porphyrin in these metal-assembled dendrimers also support the stepwise complexation of the metal ion. These analyses suggest that the finely assembled metal complexes in a dendrimer architecture strongly affect the electronic status of the porphyrin core. Results from transient absorption measurements strongly indicate a very fast electron transfer on a subpicosecond time scale between the core and assembled metal complexes.

Metal-Assembling Dendrimers with a Triarylamine Core and Their Application to a Dye-Sensitized Solar Cell

N. Satoh, T. Nakashima, K. Yamamoto
J. Am. Chem. Soc. 2005, 127, 13030-13038.

Metal-Assembling Dendrimers with a Triarylamine Core and Their Application to a Dye-Sensitized Solar Cell

A series of charge-separable and hole-transporting phenylazomethine dendrimers with a triarylamine core are prepared and evaluated for use as a charge separator in dye-sensitized solar cells (DSSCs). Triphenylamine with dendric phenylazomethine (TPA-DPA) is prepared by synthesizing up to five generations of dendrons using a convergent method. The resultant dendrimer has a rigid sphere structure similar to globular protein, with a hydrodynamic radius of 2.43 nm. Electrochemical oxidation of the TPA core reveals that the dendron units in the dendrimer have 0.35 of the attenuation factor (β) in the electron transfer. Complexation of TPA-DPA with SnCl2 proceeds in stepwise fashion from the core to the terminal imine following the basicity gradient among imine groups in each dendron shell. DSSCs prepared by casting these dendrimers onto dye-sensitized TiO2 film exhibited a higher open-circuit voltage than the bare film through the suppression of back electron transfer. The generational growth of dendrons increases the radius of the dendrimer, resulting in a stronger association with I3- and higher open-circuit voltage with an increasing number of generations. Complexation with SnCl2 reduces the resistance of TPA-DPA and improves the fill factor. The energy conversion efficiency of the DSSC prepared using fifth-generation TPA-DPA is 21% higher than that for the bare film and, when complexed with SnCl2, provides a 34% improvement.

Fine Control of the Release and Encapsulation of Fe Ions in Dendrimers through Ferritin-like Redox Switching

R. Nakajima, M. Tsuruta, M. Higuchi, K. Yamamoto
J. Am. Chem. Soc. 2004, 126, 1630-1631.

Fine Control of the Release and Encapsulation of Fe Ions in Dendrimers through Ferritin-like Redox Switching

Numerous dendrimers incorporating metal ions or clusters have received much attention as catalytic and drug delivery materials. We expanded the variety of metal ions that complex with DPA through a radial stepwise complexation to create novel organic−inorganic hybrid materials. As one of the most common and significant iron ions, Fe3+ was used. It was confirmed that iron ions, FeCl3, are coordinated to the imine groups of a spherical phenylazomethine dendrimer (DPA) in a stepwise radial fashion, which should make it possible to control the number and location of the Fe3+ ions incorporated into the dendrimers. Iron possesses very interesting properties such as magnetism, redox chemistry, and catalysis and is also one of the essential elements of our body. Here, we show the first successful attempt to control the biomimetic switching of iron ions' release/encapsulation in the dendrimer driven by their redox response of the Fe2+/Fe3+ couple, which might find uses as a drug delivery system.

Control of Stepwise Radial Complexation in Dendritic Polyphenylazomethines

M. Higuchi, M. Tsuruta, H. Chiba, S. Shiki, K. Yamamoto
J. Am. Chem. Soc. 2003, 125, 9988-9997.

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 SnCl2 molecules, because the imine group is complexed with SnCl2 at a ratio of 1:1. During addition of 30 equiv of SnCl2 to DPA G4, four shifts in the isosbestic point were observed in the UV−vis spectra, and the amount of SnCl2 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 SnCl2 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 13C 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 Triarylamine Dendrimers as a Hole-Transport Material with a Controlled Metal-Assembling Function

N. Satoh, J. Cho, M. Higuchi, K. Yamamoto
J. Am. Chem. Soc. 2003, 125, 8104-8105.

Novel Triarylamine Dendrimers as a Hole-Transport Material with a Controlled Metal-Assembling Function

A series of phenylazomethine dendrimers with a triarylamine core (TPA−DPA) were synthesized by dehydration using TiCl4. The complexation of the fourth genereration (G4) TPA−DPA with SnCl2 proceeds in not a random but a stepwise fashion from the core to the terminal imines of the G4 dendrimer. The molecular size of TPA−DPA G4 is larger than that of DPA G4 in THF solution and has a rigid sphere structure like a globular protein. Organic light-emitting diodes (OLEDs) were fabricated, and the EL performances of the devices using the TPA−DPA−metal complexes as the hole-transport materials are drastically increased (ca. 20 times) by metal complexation.

Metal Assembly in Novel Dendrimers with Porphyrin Cores

T. Imaoka, H. Horiguchi, K. Yamamoto
J. Am. Chem. Soc. 2003, 125, 340-341.

Metal Assembly in Novel Dendrimers with Porphyrin Cores

A series of phenylazozmethine (DPA) dendrimers with a porphyrin core (PnH2) were synthesized by dehydration using TiCl4 from meso-tetrakis(4-aminophenyl)porphyrin and the DPA dendrons. The addition of SnCl2 to a dichloromethane/acetonitrile solution of dendritic cobalt porphyrin resulted in a stepwise spectral change. By using UV−vis spectroscopy to monitor the complexation of the P4CoIIICl until an equimolar amount of SnCl2 has been added, four changes in the position of the isosbestic point were observed during the addition of SnCl2. Titration results suggest that four different complexes are successively formed upon the SnCl2 addition and that the complexation proceeds in, not a random, but a stepwise fashion from the core imines to the terminal imines of P4CoIIICl. The electrochemical study reveals that their dendrimers with Tb ion act as a multielectron mediator in CO2 reduction at high applied potential on the electrode.

Stepwise radial complexation of imine groups in phenylazomethine dendrimers

K. Yamamoto, M. Higuchi, S. Shiki, M. Tsuruta, H. Chiba
Nature 2002, 415, 509-511.

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. The unusual, tree-like topology endows these nanometre-sized macromolecules with a gradient in branch density from the interior to the exterior, which can give rise to an energy gradient that directs the transfer of charge and energy from the dendrimer periphery to its coreHere we show that tin ions, Sn2+, complex to the imine groups of a spherical polyphenylazomethine dendrimer in a stepwise fashion. This behaviour reflects a gradient in the electron density associated with the imine groups, 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 find uses as tailored catalysts or building blocks for advanced materials.

First Synthesis of Phenylazomethine Dendrimer Ligands and Structural Studies

M. Higuchi, S. Shiki, K. Ariga, K. Yamamoto
J. Am. Chem. Soc. 2001, 123, 4414-4420.

First Synthesis of Phenylazomethine Dendrimer Ligands and Structural Studies

Novel dendritic polyphenylazomethines (DPAs), which consist of a π-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 (Td10% 521 °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 P21/a, a = 25.352(4) Å, b = 8.577(2) Å, c = 16.151(2) Å, β = 106.25(1)°, V = 3371.6(10) Å3, Z = 2, Dcalc = 1.168 g/cm3, μ(Cu Kα) = 0.536 cm-1, final R = 0.089, and Rw = 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 π−A measurements to be 3.8−4.2 nm2 (the calculated diameter 2.2−2.3 nm, which agreed with the TEM result). NMR studies (1H NMR at 130 °C and T1 measurements) supported a conformational rigidity of DPA G4 in solution.