Browsing by Author "Tobe, Yoshito"

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[2.2.2.2](2,7)-1-Bromonaphthalenophane from a Desymmetrized Building Block Bearing Electrophilic and Masked Nucleophilic Functionalities
(2019-03-01)
Cai, Guangke
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Chatterjee, Shreyam
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Hisaki, Ichiro
;
Tobe, Yoshito
;
應用化學系
In search of 2,7-ethylene-bridged naphthalenophanes with desymmetrized naphthalene cores as inherently chiral cyclophanes, nucleophilic substitution of 1-bromo-7-(bromomethyl)-2-[(trimethylsilyl)methyl]naphthalene, a desymmetrized building block bearing an electrophilic group (CH2Br) and a masked nucleophilic functionality (CH2TMS) which can be activated by fluoride anion, was examined. As a result, in contrast to the case of parent naphthalenophanes wherein the smallest [2.2]naphthalenophane was obtained as the major product, only [2.2.2.2](2,7)-1-bromonaphthalenophane was obtained albeit in low yields, whereas the corresponding [2.2]- or [2.2.2]naphthalenophanes were not obtained. Though the [2.2.2.2]-1-bromonaphthalenophane can adopt four idealized geometries of different symmetry, among which three are inherently chiral, theoretical calculations predict that three conformers have almost equal energy and may equilibrate in solution. The X-ray crystallographic study shows that it adopts a C-2 conformation with anti,anti,anti orientation of the C-Br bonds at least as a major component in crystal.
9,10-Dihydro-as-indacenodithiophenes: Isomers with an asIndacene Core
(2019-04-05)
Miyoshi, Hirokazu
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Nabe, Akino
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Chatterjee, Shreyam
;
Tobe, Yoshito
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應用化學系
Two isomers of 9,10-dihydro-as-indacenodithiophenes (DIDTs) and the corresponding diketones having an as-indacene core were synthesized. Their thermal, photophysical, and electrochemical properties were investigated, revealing that they depend on the direction of the fusion of the thiophene rings. For the DIDTs, the effect of the mode of ring fusion on the physical properties is discussed by comparison with the previously reported derivatives of DIDT isomers with an s-indacene core. The observed difference between the highest occupied molecular orbital (HOMO)/ lowest unoccupied molecular orbital (LUMO) levels of the DIDT isomers is ascribed to the efficiency of 7z-conjugation, which depends on a- or f3-linkage between the terminal thiophenes with the central benzene ring. In addition, the effect of the peripheral aromatic ring (thiophene or benzene) is elucidated by comparison with indeno[2,1-a]fluorene (DIF) bearing an as-indacene core. The HOMO levels of DIDTs are significantly raised compared to that of structurally related DIF because of electron-donating character of the thiophene rings. For the DIDT diketones, structural effect due to the proximate carbonyl groups is discussed by comparison with the isomers with remote carbonyl groups. In diketones bearing proximate carbonyl groups, the LUMO levels are destabilized owing to antibonding interaction between the carbonyl oxygen atoms, resulting in approach of the LUMO and LUMO+1 energy levels.
A Lucky Encounter that Triggered a Leap
(2020-02-01)
Tobe, Yoshito
;
應用化學系
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Department of Applied Chemistry
Alkoxy Chain Number Effect on Self-Assembly of a Trigonal Molecule at the Liquid/Solid Interface
(2019-11-07)
Tahara, Kazukuni
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Nakayama, Ruri
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Maeda, Matsuhiro
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De Feyter, Steven
;
Tobe, Yoshito
We herein investigated the effect of the number of alkoxy chains on the two-dimensional self-assembly of a trigonal molecular building block. To this end, a dehydrobenzo[12]-annulene (DBA) derivative, DBA-OC14-OC1 having three tetradecyloxy chains and three methoxy groups in an alternating manner, was synthesized. Scanning tunneling microscopy (STM) observations at the 1,2,4-trichlorobenzene (TCB)/graphite interface revealed that DBA-OC14-OC1 forms three monolayer structures: porous honeycomb, parallelogram, and hexagonal A structures. At the 1-phenyloctane (PO)/graphite interface, DBA-OC14-OC1 also forms three structures: parallelogram, hexagonal B, and dense linear structures. In contrast to the previously reported DBA derivative DBA-OC14 having six tetradecyloxy chains, DBA-OC14-OC1 shows structural polymorphism with a variety of alkyl chain interaction modes. Because in the observed patterns DBA-OC14-OC1 adopts a low symmetric C-s or C-1 geometry, the variation of the interaction modes and the resulting network patterns likely originate from the conformational flexibility on surface of this DBA by decreasing the number of alkyl chains. Molecular mechanics simulations gave insight into the structural and energy aspects of this pattern formation. We also discussed the role of solvents, TCB and PO, on the polymorph formation.
An Approach to the Synthesis of a Two-Dimensional Polymer Using a Preorganized Host-Guest Network by Self-Assembly at the Liquid/Solid Interface
(1970-01-01)
Iritani, Kohei
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Kaneko, Kyohei
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Tahara, Kazukuni
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De Feyter, Steven
;
Tobe, Yoshito
An approach to synthesize a two-dimensional polymer (2DP) using a preorganized host-guest network at the liquid/solid interface is presented. As a host network, we used a self-assembled monolayer of a dehydrobenzo[12]annulene derivative having aminophenyl groups at three alkoxy chain ends and, as a guest, a hexakis(phenylethynyl)benzene derivative having six formyl groups, aiming to connect the host to the guest embedded in the host matrix by imine bond formation. STM observations of host-guest mixtures with trifluoroacetic acid at the 1-phenyloctane/highly oriented pyrolytic graphite interface revealed that the guest was observed as a spoke-like feature in the nanowells. Based on the STM image analysis, short distances between the diagonal phenyl groups in the nanowells are detected, indicating that the imine bonds are formed. However, the small abundance and random distribution of the short phenyl-phenyl distance indicate that the periodically ordered 2DP structure is not formed, probably because the network cannot tolerate the structural change due to partial bond formation.
Electrostatically Driven Guest Binding in Self-Assembled Molecular Network of Hexagonal Pyridine Macrocycle at the Liquid/Solid Interface: Symmetry Breaking Induced by Coadsorbed Solvent Molecules
(2019-11-26)
Iritani, Kohei
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Takeda, Hiroshi
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Kather, Michael
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Yokoi, Masahiko
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Moeglen, Magali
We present here the construction of a self-assembled two-dimensional network at the liquid/solid interface using a hexagonal pyridine macrocycle which binds an organic cation in its intrinsic porous space by electrostatic interactions. For this purpose, a hexagonal pyridinylene-butadiynylene macrocycle (PyBM) having six octyloxymethyl groups, PyBM-C8, was synthesized. As guests, tropylium (Tr) tetrafluoroborate and trioxatriangulenium (TOTA) hexafluorophosphate were used. In this study, we focused on (i) the network patterns of PyBM-C8 which change in response to its concentration and (ii) the position of the guest immobilized in the porous space of the macrocycle. Scanning tunneling microscopy (STM) observations at the interface of 1,2,4-trichlorobenzene (TCB) and highly oriented pyrolytic graphite (HOPG) revealed that PyBM-C8 formed four different polymorphs, oblique, loose hexagonal, linear, and rectangular, depending on the solute concentration and annealing treatment. Solvent TCB molecules are likely coadsorbed to not only the intrinsically porous space of PyBM-C8 (internal TCB) but also the space outside of the macrocycle between its alkyl chains (external TCB) in most of the cases. Upon adding the guest cation, whereas small Tr was not visualized in the pore due to size mismatching, larger TOTA was clearly observed in each pore. In addition, based on high-resolution STM images of the rhombus packing pattern of PyBM-C8, we revealed experimentally that TOTA was placed at an off center position of the deformed hexagonal macrocyclic core in the rhombus pattern. On the basis of the molecular mechanics calculations, we hypothesize that the off-center location of TOTA is due to deformation of the hexagonal macrocycle through interaction with two external TCB molecules located at opposite edges of the macrocyclic core. Symmetry breaking of the macrocyclic host framework induced by coadsorbed surrounding solvent molecules thus plays a significant role in host-guest complexation at the liquid/solid interface.
Hierarchical two-dimensional molecular assembly through dynamic combination of conformational states at the liquid/solid interface
(2020-09-14)
Maeda, Matsuhiro
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Nakayama, Ruri
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De Feyter, Steven
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Tobe, Yoshito
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Tahara, Kazukuni
Self-sorting of multiple building blocks for correctly positioning molecules through orthogonal recognition is a promising strategy for construction of a hierarchical self-assembled molecular network (SAMN) on a surface. Herein we report that a trigonal molecule, dehydrobenzo[12]annulene (DBA) derivative having three tetradecyloxy chains and three hydroxy groups in an alternating manner, forms hierarchical triangular clusters of different sizes ranging from 2.4 to 16.4 nm, consisting of 3 to 78 molecules, respectively, at the liquid/graphite interface. The key is the dynamic combination of three different conformational states, which is solvent and concentration dependent. The present knowledge extends design strategies for production of sophisticated hierarchical SAMNs using a single component at the liquid/solid interface.
On-Surface Evolution of meso-Isomerism in Two-Dimensional Supramolecular Assemblies
(2019-07-08)
Park, Juyeon
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Kim, Ju-Hyung
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Bak, Sunmi
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Tahara, Kazukuni
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Jung, Jaehoon
Chiral structures created through the adsorption of molecules onto achiral surfaces play pivotal roles in many fields of science and engineering. Here, we present a systematic study of a novel chiral phenomenon on a surface in terms of organizational chirality, that is, meso-isomerism, through coverage-driven hierarchical polymorphic transitions of supramolecular assemblies of highly symmetric pi-conjugated molecules. Four coverage-dependent phases of dehydrobenzo[12]annulene were uniformly fabricated on Ag(111), exhibiting unique chiral characteristics from the single-molecule level to two-dimensional supramolecular assemblies. All coverage-driven phase transitions stem from adsorption-induced pseudo-diastereomerism, and our observation of a lemniscate-type (infinity) supramolecular configuration clearly reveals a drastic chiral phase transition from an enantiomeric chiral domain to a meso-isomeric achiral domain. These findings provide new insights into controlling two-dimensional chiral architectures on surfaces.
Porous Self-Assembled Molecular Networks as Templates for Chiral-Position-Controlled Chemical Functionalization of Graphitic Surfaces
(2020-04-22)
Tahara, Kazukuni
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Kubo, Yuki
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Hashimoto, Shingo
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Ishikawa, Toru
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Kaneko, Hiromasa
Controlled covalent functionalization of graphitic surfaces with molecular scale precision is crucial for tailored modulation of the chemical and physical properties of carbon materials. We herein present that porous self-assembled molecular networks (SAMNs) act as nanometer scale template for the covalent electrochemical functionalization of graphite using an aryldiazonium salt. Hexagonally aligned achiral grafted species with lateral periodicity of 2.3, 2.7, and 3.0 nm were achieved utilizing SAMNs having different pore-to-pore distances. The unit cell vectors of the grafted pattern match those of the SAMN. After the covalent grafting, the template SAMNs can be removed by simple washing with a common organic solvent. We briefly discuss the mechanism of the observed pattern transfer. The unit cell vectors of the grafted pattern align along nonsymmetry axes of graphite, leading to mirror image grafted domains, in accordance with the domain-specific chirality of the template. In the case in which a homochiral building block is used for SAMN formation, one of the 2D mirror image grafted patterns is canceled. This is the first example of a nearly crystalline one-sided or supratopic covalent chemical functionalization. In addition, the positional control imposed by the SAMN renders the functionalized surface (homo)chiral reaching a novel level of control for the functionalization of carbon surfaces, including surface-supported graphene.
Reversing the Handedness of Self-Assembled Porous Molecular Networks through the Number of Identical Chiral Centres
(2019-06-03)
Tahara, Kazukuni
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Noguchi, Aya
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Nakayama, Ruri
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Ghijsens, Elke
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De Feyter, Steven
Scanning tunnelling microscope observations at the 1-phenyloctane/graphite interface reveal how chiral structural information at the molecular level is transferred and expressed structurally at the 2D supramolecular level for a porous system. The chirality of self-assembled molecular networks formed by chiral dehydrobenzo[12]annulene (cDBA) derivatives having three chiral chains and three achiral chains, alternatingly, is compared with those of cDBAs having six chiral chains reported previously. While for all cDBAs homochiral surfaces are formed, their handedness is not simply a reflection of the absolute configuration of the stereogenic centres. Both the number of stereogenic centres as well as the length of the achiral chains determine the supramolecular handedness, providing a deep insight into the supramolecular chirality induction mechanisms at play. Moreover, these cDBAs act to induce chirality in porous networks formed by achiral DBAs.
Stereospecific Epitaxial Growth of Bilayered Porous Molecular Networks
(2020-05-13)
Fang, Yuan
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Lindner, Benjamin D.
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Destoop, Iris
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Tsuji, Takashi
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Zhang, Zhenzhe
Stereocontrolled multilayer growth of supramolecular porous networks at the interface between graphite and a solution was investigated. For this study, we designed a chiral dehydrobenzo[12]annulene (DBA) building block bearing alkoxy chains substituted at the 2 position with hydroxy groups, which enable van der Waals stabilization in a layer and potential hydrogen-bonding interactions between the layers. Bias voltage-dependent scanning tunneling microscopy (STM) experiments revealed the diastereospecificity of the bilayer with respect to both the intrinsic chirality of the building blocks and the supramolecular chirality of the self-assembled networks. Top and bottom layers within the same crystalline domain were composed of the same enantiomers but displayed opposite supramolecular chiralities.
Trapping a pentagonal molecule in a self-assembled molecular network: an alkoxylated isosceles triangular molecule does the job
(2020-05-18)
Anzai, Masaru
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Iyoda, Masahiko
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De Feyter, Steven
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Tobe, Yoshito
;
Tahara, Kazukuni
We herein report a unique example of on-surface adaptive self-assembly. A pentagon-shaped macrocycle, cyclic [5]meta-phenyleneacetylene [5]CMPA, is trapped by the adaptive supramolecular network formed by an isosceles triangular molecule, alkoxy substituted dehydrobenzo[14]annulene [14]ISODBA at the liquid/graphite interface, leading to a highly ordered and large-area bicomponent self-assembled molecular network (SAMN), as revealed by scanning tunneling microscopy (STM).