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Steven De Feyter - One of the best experts on this subject based on the ideXlab platform.
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Electrostatically Driven Guest Binding in a Self-Assembled Porous Network at the Liquid/Solid Interface
2018Co-Authors: Kohei Iritani, Steven De Feyter, Kazukuni Tahara, Motoki Ikeda, Anna Yang, Keiji Hirose, Jeffrey S Moore, Masaru Anzai, Yoshito TobeAbstract:We present here the construction of a self-assembled two-dimensional (2D) porous monolayer bearing a highly polar 2D space to study guest co-adsorption through electrostatic interactions at the liquid/Solid Interface. For this purpose, a dehydrobenzo[12]annulene (DBA) derivative, DBA-TeEG, having tetraethylene glycol (TeEG) groups at the end of the three alternating alkoxy chains connected by p-phenylene linkers was synthesized. As a reference host molecule, DBA-C10, having nonpolar C10 alkyl chains at three alternating terminals, was employed. As guest molecules, hexagonal phenylene–ethynylene macrocycles (PEMs) attached by triethylene glycol (TEG) ester and hexyl ester groups, PEM-TEG and PEM-C6, respectively, at each vertex of the macrocyclic periphery were used. Scanning tunneling microscopy observations at the 1,2,4-trichlorobenzene/highly oriented pyrolytic graphite Interface revealed that PEM-TEG was immobilized in the pores formed by DBA-TeEG at higher probability because of electrostatic interactions such as dipole–dipole and hydrogen bonding interactions between oligoether units of the host and guest, in comparison to PEM-C6 with nonpolar groups. These observations are discussed based on molecular mechanics simulations to investigate the role of the polar functional groups. When a nonpolar host matrix formed by DBA-C10 was used, however, only phase separation and preferential adsorption were observed; virtually no host–guest complexation was discernible. This is ascribed to the strong affinity between the guest molecules which form by themselves densely packed van der Waals networks on the surface
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Odd–Even Effects in Chiral Phase Transition at the Liquid/Solid Interface
2017Co-Authors: Hai Cao, Yoshito Tobe, Kazukuni Tahara, Shintaro Itano, Steven De FeyterAbstract:Chiral selection on inorganic crystalline surfaces represents one of the most promising avenues to the separation of enantiomers. However, there are competing influences at play: on the one hand, the confinement to the surface seems to enhance chiral discrimination between enantiomers; on the other hand, racemic patterns tend to possess higher packing density therewith higher stability. A clear picture on the delicate balance between these two opposing factors is missing. We address this issue in monolayers of alkylated dehydrobenzo[12]annulene (DBA) derivatives at the liquid/Solid Interface by a detailed investigation of the relationship between packing density and 2D chirality. We report on chiral phase transitions, evolving from homochiral low density porous networks to enantiomeric excess, racemic, or homochiral densely packed structures, by using scanning tunneling microscopy (STM) as a visualization tool. The changes in monolayer chirality in response to increased packing density, however, are strongly correlated with molecular structural features such as the length of the alkyl chains and in particular their parity. While heterochiral lattices are indeed denser than its enantiomorphous counterparts, close packing does not necessarily favor racemic crystallization: the azimuthal orientation of building blocks in a domain may play a decisive role. In light of the popularity of using alkyl chains to adhere molecules onto a surface, we believe that our findings may have implications for predictive chiral recognition and resolution processes
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dynamic control over supramolecular handedness by selecting chiral induction pathways at the solution Solid Interface
Nature Chemistry, 2016Co-Authors: Yuan Fang, Kazukuni Tahara, Elke Ghijsens, Yoshito Tobe, Kunal S Mali, Hai Cao, Oleksandr Ivasenko, Aya Noguchi, Steven De FeyterAbstract:A dominant theme within the research on two-dimensional chirality is the sergeant–soldiers principle, wherein a small fraction of chiral molecules (sergeants) is used to skew the handedness of achiral molecules (soldiers) to generate a homochiral surface. Here, we have combined the sergeant–soldiers principle with temperature-dependent molecular self-assembly to unravel a peculiar chiral amplification mechanism at the solution–Solid Interface in which, depending on the concentration of a sergeant–soldiers solution, the majority handedness of the system can either be amplified or entirely reversed after an annealing step, furnishing a homochiral surface. Two discrete pathways that affect different stages of two-dimensional crystal growth are invoked for rationalizing this phenomenon and we present a set of experiments where the access to each pathway can be precisely controlled. These results demonstrate that a detailed understanding of subtle intermolecular and interfacial interactions can be used to induce drastic changes in the handedness of a supramolecular network. The formation of homochiral supramolecular networks at solution–Solid Interfaces typically relies on the soldier-and-sergeant approach, in which a small amount of chiral modifier defines the handedness of the network. Now, judicious choice of the sergeant, solvent, temperature and concentration has enabled chiral induction pathways to be controlled so that a homochiral surface of either handedness can be assembled from the same system.
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reversible local and global switching in multicomponent supramolecular networks controlled guest release and capture at the solution Solid Interface
ACS Nano, 2015Co-Authors: Shernlong Lee, Kunal S Mali, Klaus Mullen, Yuan Fang, Gangamallaiah Velpula, F P Cometto, Magali Lingenfelder, Steven De FeyterAbstract:Dynamically switchable supramolecular systems offer exciting possibilities in building smart surfaces, the structure and thus the function of which can be controlled by using external stimuli. Here we demonstrate an elegant approach where the guest binding ability of a supramolecular surface can be controlled by inducing structural transitions in it. A physisorbed self-assembled network of a simple hydrogen bonding building block is used as a switching platform. We illustrate that the reversible transition between porous and nonporous networks can be accomplished using an electric field or applying a thermal stimulus. These transitions are used to achieve controlled guest release or capture at the solution–Solid Interface. The electric field and the temperature-mediated methods of guest release are operative at different length scales. While the former triggers the transition and thus guest release at the nanometer scale, the latter is effective over a much larger scale. The flexibility associated with ph...
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flow assisted 2d polymorph selection stabilizing metastable monolayers at the liquid Solid Interface
Journal of the American Chemical Society, 2014Co-Authors: Shernlong Lee, Zhongyi Yuan, Long Chen, Kunal S Mali, Klaus Mullen, Steven De FeyterAbstract:Controlling crystal polymorphism constitutes a formidable challenge in contemporary chemistry. Two-dimensional (2D) crystals often provide model systems to decipher the complications in 3D crystals. In this contribution, we explore a unique way of governing 2D polymorphism at the organic liquid–Solid Interface. We demonstrate that a directional solvent flow could be used to stabilize crystalline monolayers of a metastable polymorph. Furthermore, flow fields active within the applied flow generate millimeter-sized domains of either polymorph in a controlled and reproducible fashion.
Yoshito Tobe - One of the best experts on this subject based on the ideXlab platform.
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Electrostatically Driven Guest Binding in a Self-Assembled Porous Network at the Liquid/Solid Interface
2018Co-Authors: Kohei Iritani, Steven De Feyter, Kazukuni Tahara, Motoki Ikeda, Anna Yang, Keiji Hirose, Jeffrey S Moore, Masaru Anzai, Yoshito TobeAbstract:We present here the construction of a self-assembled two-dimensional (2D) porous monolayer bearing a highly polar 2D space to study guest co-adsorption through electrostatic interactions at the liquid/Solid Interface. For this purpose, a dehydrobenzo[12]annulene (DBA) derivative, DBA-TeEG, having tetraethylene glycol (TeEG) groups at the end of the three alternating alkoxy chains connected by p-phenylene linkers was synthesized. As a reference host molecule, DBA-C10, having nonpolar C10 alkyl chains at three alternating terminals, was employed. As guest molecules, hexagonal phenylene–ethynylene macrocycles (PEMs) attached by triethylene glycol (TEG) ester and hexyl ester groups, PEM-TEG and PEM-C6, respectively, at each vertex of the macrocyclic periphery were used. Scanning tunneling microscopy observations at the 1,2,4-trichlorobenzene/highly oriented pyrolytic graphite Interface revealed that PEM-TEG was immobilized in the pores formed by DBA-TeEG at higher probability because of electrostatic interactions such as dipole–dipole and hydrogen bonding interactions between oligoether units of the host and guest, in comparison to PEM-C6 with nonpolar groups. These observations are discussed based on molecular mechanics simulations to investigate the role of the polar functional groups. When a nonpolar host matrix formed by DBA-C10 was used, however, only phase separation and preferential adsorption were observed; virtually no host–guest complexation was discernible. This is ascribed to the strong affinity between the guest molecules which form by themselves densely packed van der Waals networks on the surface
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hexagonal molecular tiling by hexagonal macrocycles at the liquid Solid Interface structural effects on packing geometry
Langmuir, 2017Co-Authors: Kohei Iritani, Kazukuni Tahara, Motoki Ikeda, Anna Yang, Keiji Hirose, Jeffrey S Moore, Yoshito TobeAbstract:We present here hexagonal tiling using hexagonal phenylene-ethynylene and phenylene-butadiynylene macrocycles attached by alkyl ester groups, PEM-C6 and PBM-C8, respectively, or triethylene glycol ester groups, PEM-TEG and PBM-TEG, respectively, at each vertex of the macrocyclic periphery at the liquid/Solid Interface. In this study, we focused on the effects of macrocyclic core size and the chemical properties of side chains attached to macrocyclic cores as well as solute concentrations on the hexagonal geometry of self-assembled monolayers. STM observations at the 1,2,4-trichrolobenzene/graphite Interface revealed that PEM-C6 formed a honeycomb structure by van der Waals interactions between the interdigitated alkyl chains. However, upon increasing solute concentration, it changed to more dense hexagonal structure (tentatively called loose hexagonal structure I). In contrast, PBM-C8 formed loose hexagonal structure II of a slightly different packing mode at low concentration, while at high concentration...
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Odd–Even Effects in Chiral Phase Transition at the Liquid/Solid Interface
2017Co-Authors: Hai Cao, Yoshito Tobe, Kazukuni Tahara, Shintaro Itano, Steven De FeyterAbstract:Chiral selection on inorganic crystalline surfaces represents one of the most promising avenues to the separation of enantiomers. However, there are competing influences at play: on the one hand, the confinement to the surface seems to enhance chiral discrimination between enantiomers; on the other hand, racemic patterns tend to possess higher packing density therewith higher stability. A clear picture on the delicate balance between these two opposing factors is missing. We address this issue in monolayers of alkylated dehydrobenzo[12]annulene (DBA) derivatives at the liquid/Solid Interface by a detailed investigation of the relationship between packing density and 2D chirality. We report on chiral phase transitions, evolving from homochiral low density porous networks to enantiomeric excess, racemic, or homochiral densely packed structures, by using scanning tunneling microscopy (STM) as a visualization tool. The changes in monolayer chirality in response to increased packing density, however, are strongly correlated with molecular structural features such as the length of the alkyl chains and in particular their parity. While heterochiral lattices are indeed denser than its enantiomorphous counterparts, close packing does not necessarily favor racemic crystallization: the azimuthal orientation of building blocks in a domain may play a decisive role. In light of the popularity of using alkyl chains to adhere molecules onto a surface, we believe that our findings may have implications for predictive chiral recognition and resolution processes
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dynamic control over supramolecular handedness by selecting chiral induction pathways at the solution Solid Interface
Nature Chemistry, 2016Co-Authors: Yuan Fang, Kazukuni Tahara, Elke Ghijsens, Yoshito Tobe, Kunal S Mali, Hai Cao, Oleksandr Ivasenko, Aya Noguchi, Steven De FeyterAbstract:A dominant theme within the research on two-dimensional chirality is the sergeant–soldiers principle, wherein a small fraction of chiral molecules (sergeants) is used to skew the handedness of achiral molecules (soldiers) to generate a homochiral surface. Here, we have combined the sergeant–soldiers principle with temperature-dependent molecular self-assembly to unravel a peculiar chiral amplification mechanism at the solution–Solid Interface in which, depending on the concentration of a sergeant–soldiers solution, the majority handedness of the system can either be amplified or entirely reversed after an annealing step, furnishing a homochiral surface. Two discrete pathways that affect different stages of two-dimensional crystal growth are invoked for rationalizing this phenomenon and we present a set of experiments where the access to each pathway can be precisely controlled. These results demonstrate that a detailed understanding of subtle intermolecular and interfacial interactions can be used to induce drastic changes in the handedness of a supramolecular network. The formation of homochiral supramolecular networks at solution–Solid Interfaces typically relies on the soldier-and-sergeant approach, in which a small amount of chiral modifier defines the handedness of the network. Now, judicious choice of the sergeant, solvent, temperature and concentration has enabled chiral induction pathways to be controlled so that a homochiral surface of either handedness can be assembled from the same system.
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role of substrate in directing the self assembly of multicomponent supramolecular networks at the liquid Solid Interface
ACS Nano, 2012Co-Authors: Tatyana Balandina, Kazukuni Tahara, Yoshito Tobe, Jinne Adisoejoso, Nadja Sandig, Matthew O Blunt, Shengbin Lei, Francesco Zerbetto, Steven De FeyterAbstract:The self-assembly of multicomponent networks at the liquid–Solid Interface between Au(111) or highly oriented pyrolytic graphite (HOPG) and organic solvents was investigated using scanning tunneling microscopy. Alkoxylated dehydrobenzo[12]annulene (DBA) derivatives form hexagonal nanoporous networks, which trap either single molecules of coronene (COR) or small clusters of COR and isophthalic acid to form multicomponent networks. The pattern of interdigitation between alkyl chains from DBA molecules produces hexagonal pores that are either chiral or achiral. On Au(111) substrates multicomponent networks display an ordered superlattice arrangement of chiral and achiral pores. In comparison, similar networks on HOPG display only chiral pores. The unique superlattice structure observed on Au(111) is related to a lower energetic preference for chiral pores than on HOPG and increased diffusion barriers for guest molecules. The increased diffusion barriers for guests allow them to act as nucleation sites for th...
Kazukuni Tahara - One of the best experts on this subject based on the ideXlab platform.
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Electrostatically Driven Guest Binding in a Self-Assembled Porous Network at the Liquid/Solid Interface
2018Co-Authors: Kohei Iritani, Steven De Feyter, Kazukuni Tahara, Motoki Ikeda, Anna Yang, Keiji Hirose, Jeffrey S Moore, Masaru Anzai, Yoshito TobeAbstract:We present here the construction of a self-assembled two-dimensional (2D) porous monolayer bearing a highly polar 2D space to study guest co-adsorption through electrostatic interactions at the liquid/Solid Interface. For this purpose, a dehydrobenzo[12]annulene (DBA) derivative, DBA-TeEG, having tetraethylene glycol (TeEG) groups at the end of the three alternating alkoxy chains connected by p-phenylene linkers was synthesized. As a reference host molecule, DBA-C10, having nonpolar C10 alkyl chains at three alternating terminals, was employed. As guest molecules, hexagonal phenylene–ethynylene macrocycles (PEMs) attached by triethylene glycol (TEG) ester and hexyl ester groups, PEM-TEG and PEM-C6, respectively, at each vertex of the macrocyclic periphery were used. Scanning tunneling microscopy observations at the 1,2,4-trichlorobenzene/highly oriented pyrolytic graphite Interface revealed that PEM-TEG was immobilized in the pores formed by DBA-TeEG at higher probability because of electrostatic interactions such as dipole–dipole and hydrogen bonding interactions between oligoether units of the host and guest, in comparison to PEM-C6 with nonpolar groups. These observations are discussed based on molecular mechanics simulations to investigate the role of the polar functional groups. When a nonpolar host matrix formed by DBA-C10 was used, however, only phase separation and preferential adsorption were observed; virtually no host–guest complexation was discernible. This is ascribed to the strong affinity between the guest molecules which form by themselves densely packed van der Waals networks on the surface
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hexagonal molecular tiling by hexagonal macrocycles at the liquid Solid Interface structural effects on packing geometry
Langmuir, 2017Co-Authors: Kohei Iritani, Kazukuni Tahara, Motoki Ikeda, Anna Yang, Keiji Hirose, Jeffrey S Moore, Yoshito TobeAbstract:We present here hexagonal tiling using hexagonal phenylene-ethynylene and phenylene-butadiynylene macrocycles attached by alkyl ester groups, PEM-C6 and PBM-C8, respectively, or triethylene glycol ester groups, PEM-TEG and PBM-TEG, respectively, at each vertex of the macrocyclic periphery at the liquid/Solid Interface. In this study, we focused on the effects of macrocyclic core size and the chemical properties of side chains attached to macrocyclic cores as well as solute concentrations on the hexagonal geometry of self-assembled monolayers. STM observations at the 1,2,4-trichrolobenzene/graphite Interface revealed that PEM-C6 formed a honeycomb structure by van der Waals interactions between the interdigitated alkyl chains. However, upon increasing solute concentration, it changed to more dense hexagonal structure (tentatively called loose hexagonal structure I). In contrast, PBM-C8 formed loose hexagonal structure II of a slightly different packing mode at low concentration, while at high concentration...
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Odd–Even Effects in Chiral Phase Transition at the Liquid/Solid Interface
2017Co-Authors: Hai Cao, Yoshito Tobe, Kazukuni Tahara, Shintaro Itano, Steven De FeyterAbstract:Chiral selection on inorganic crystalline surfaces represents one of the most promising avenues to the separation of enantiomers. However, there are competing influences at play: on the one hand, the confinement to the surface seems to enhance chiral discrimination between enantiomers; on the other hand, racemic patterns tend to possess higher packing density therewith higher stability. A clear picture on the delicate balance between these two opposing factors is missing. We address this issue in monolayers of alkylated dehydrobenzo[12]annulene (DBA) derivatives at the liquid/Solid Interface by a detailed investigation of the relationship between packing density and 2D chirality. We report on chiral phase transitions, evolving from homochiral low density porous networks to enantiomeric excess, racemic, or homochiral densely packed structures, by using scanning tunneling microscopy (STM) as a visualization tool. The changes in monolayer chirality in response to increased packing density, however, are strongly correlated with molecular structural features such as the length of the alkyl chains and in particular their parity. While heterochiral lattices are indeed denser than its enantiomorphous counterparts, close packing does not necessarily favor racemic crystallization: the azimuthal orientation of building blocks in a domain may play a decisive role. In light of the popularity of using alkyl chains to adhere molecules onto a surface, we believe that our findings may have implications for predictive chiral recognition and resolution processes
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dynamic control over supramolecular handedness by selecting chiral induction pathways at the solution Solid Interface
Nature Chemistry, 2016Co-Authors: Yuan Fang, Kazukuni Tahara, Elke Ghijsens, Yoshito Tobe, Kunal S Mali, Hai Cao, Oleksandr Ivasenko, Aya Noguchi, Steven De FeyterAbstract:A dominant theme within the research on two-dimensional chirality is the sergeant–soldiers principle, wherein a small fraction of chiral molecules (sergeants) is used to skew the handedness of achiral molecules (soldiers) to generate a homochiral surface. Here, we have combined the sergeant–soldiers principle with temperature-dependent molecular self-assembly to unravel a peculiar chiral amplification mechanism at the solution–Solid Interface in which, depending on the concentration of a sergeant–soldiers solution, the majority handedness of the system can either be amplified or entirely reversed after an annealing step, furnishing a homochiral surface. Two discrete pathways that affect different stages of two-dimensional crystal growth are invoked for rationalizing this phenomenon and we present a set of experiments where the access to each pathway can be precisely controlled. These results demonstrate that a detailed understanding of subtle intermolecular and interfacial interactions can be used to induce drastic changes in the handedness of a supramolecular network. The formation of homochiral supramolecular networks at solution–Solid Interfaces typically relies on the soldier-and-sergeant approach, in which a small amount of chiral modifier defines the handedness of the network. Now, judicious choice of the sergeant, solvent, temperature and concentration has enabled chiral induction pathways to be controlled so that a homochiral surface of either handedness can be assembled from the same system.
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role of substrate in directing the self assembly of multicomponent supramolecular networks at the liquid Solid Interface
ACS Nano, 2012Co-Authors: Tatyana Balandina, Kazukuni Tahara, Yoshito Tobe, Jinne Adisoejoso, Nadja Sandig, Matthew O Blunt, Shengbin Lei, Francesco Zerbetto, Steven De FeyterAbstract:The self-assembly of multicomponent networks at the liquid–Solid Interface between Au(111) or highly oriented pyrolytic graphite (HOPG) and organic solvents was investigated using scanning tunneling microscopy. Alkoxylated dehydrobenzo[12]annulene (DBA) derivatives form hexagonal nanoporous networks, which trap either single molecules of coronene (COR) or small clusters of COR and isophthalic acid to form multicomponent networks. The pattern of interdigitation between alkyl chains from DBA molecules produces hexagonal pores that are either chiral or achiral. On Au(111) substrates multicomponent networks display an ordered superlattice arrangement of chiral and achiral pores. In comparison, similar networks on HOPG display only chiral pores. The unique superlattice structure observed on Au(111) is related to a lower energetic preference for chiral pores than on HOPG and increased diffusion barriers for guest molecules. The increased diffusion barriers for guests allow them to act as nucleation sites for th...
Xueqing Yang - One of the best experts on this subject based on the ideXlab platform.
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2d co crystallization of molecular homologues promoted by size complementarity of the alkyl chains at the liquid Solid Interface
Physical Chemistry Chemical Physics, 2019Co-Authors: Xueqing Yang, Ting Chen, Dong Wang, Guang-shan Zhu, Li-jun WanAbstract:Co-crystallization of organic molecules is an important strategy for the fabrication of molecular materials. In this contribution, we investigated the mixing behavior of 5-(benzyloxy)-isophthalic acid homologues (BIC-Cn, n = 6, 8, 10, 12, and 14) at the liquid/Solid Interface using a scanning tunneling microscope. Deposition of the single component of BIC-Cn always results in typical honeycomb networks, whereas co-deposition of two BIC-Cn homologues leads to hybrid double-walled honeycomb networks or phase separation depending on the difference in the length of their alkyl chains. 2D co-crystallization can only be realized for BIC-C6/BIC-C10 or BIC-C8/BIC-C12 which have a four-methyl unit difference in their alkyl chains. The size complementarity of the alkyl chains in the two components suggests that it is responsible for the 2D co-crystallization, though hydrogen bonding contributes a lot both to the pristine honeycomb network and to the hybrid co-crystal. This result is of importance for understanding the role of van der Waals interaction and its interplay with hydrogen bonding in 2D co-crystallization.
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tri stable structural switching in 2d molecular assembly at the liquid Solid Interface triggered by external electric field
ACS Nano, 2019Co-Authors: Shu-ying Li, Xueqing Yang, Ting Chen, D. Wang, Shengfu WangAbstract:A tri-stable structural switching between different polymorphisms is presented in the 2D molecular assembly of a 5-(benzyloxy)isophthalic acid derivative (BIC-C12) at the liquid/Solid Interface. The assembled structure of BIC-C12 is sensitive to the applied voltage between the STM tip and the sample surface. A compact lamellar structure is exclusively observed at positive sample bias, while a porous honeycomb structure or a quadrangular structure is preferred at negative sample bias. Selective switching between the lamellar structure and the honeycomb structure or the quadrangular structure is realized by controlling the polarity and magnitude of the sample bias. The transition between the honeycomb structure and the quadrangular structure is, however, absent in the assembly. This tri-stable structural switching is closely related to the molecular concentration in the liquid phase. This result provides insights into the effect of external electric field on molecular assembly and benefits the design and co...
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tri stable structural switching in 2d molecular assembly at the liquid Solid Interface triggered by external electric field
ACS Nano, 2019Co-Authors: Xueqing Yang, Shengfu Wang, Ting Chen, Dong Wang, Li-jun WanAbstract:A tri-stable structural switching between different polymorphisms is presented in the 2D molecular assembly of a 5-(benzyloxy)isophthalic acid derivative (BIC-C12) at the liquid/Solid Interface. Th...
Markus Lackinger - One of the best experts on this subject based on the ideXlab platform.
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born haber cycle for monolayer self assembly at the liquid Solid Interface assessing the enthalpic driving force
Journal of the American Chemical Society, 2013Co-Authors: Wentao Song, Natalia Martsinovich, Wolfgang M Heckl, Markus LackingerAbstract:The driving force for self-assembly is the associated gain in free energy with decisive contributions from both enthalpy and entropy differences between final and initial state. For monolayer self-assembly at the liquid–Solid Interface, solute molecules are initially dissolved in the liquid phase and then become incorporated into an adsorbed monolayer. In this work, we present an adapted Born–Haber cycle for obtaining precise enthalpy values for self-assembly at the liquid–Solid Interface, a key ingredient for a profound thermodynamic understanding of this process. By choosing terephthalic acid as a model system, it is demonstrated that all required enthalpy differences between well-defined reference states can be independently and consistently assessed by both experimental and theoretical methods, giving in the end a reliable value of the overall enthalpy gain for self-assembly of interfacial monolayers. A quantitative comparison of enthalpy gain and entropy cost reveals essential contributions from solv...
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solvent dependent stabilization of metastable monolayer polymorphs at the liquid Solid Interface
ACS Nano, 2013Co-Authors: Thomas Sirtl, Wolfgang M Heckl, Wentao Song, Michael Schmittel, Georg Eder, Subhadip Neogi, Markus LackingerAbstract:Self-assembly of 1,3,5-tris(4'-biphenyl-4"-carbonitrile)benzene monolayers was studied at the liquid-Solid Interface by scanning tunneling microscopy. Application of different fatty acid homologues as solvents revealed a solvent-induced polymorphism. Yet, tempering triggered irreversible phase transitions of the initially self-assembled monolayers, thereby indicating their metastability. Interestingly, in either case, the same thermodynamically more stable and more densely packed monolayer polymorph was obtained after thermal treatment, irrespective of the initial structure. Again, the same densely packed structure was obtained in complementary solvent-free experiments conducted under ultrahigh vacuum conditions. Thus, self-assembly of metastable polymorphs at room temperature is explained by adsorption of partially solvated species under kinetic control. The irreversible phase transitions are induced by thermal desolvation, that is, desorption of coadsorbed solvent molecules.
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reversible phase transitions in self assembled monolayers at the liquid Solid Interface temperature controlled opening and closing of nanopores
Journal of the American Chemical Society, 2010Co-Authors: Rico Gutzler, Wolfgang M Heckl, Michael Schmittel, Thomas Sirtl, Jurgen F Dienstmaier, Kingsuk Mahata, Markus LackingerAbstract:We present a variable-temperature study of monolayer self-assembly at the liquid-Solid Interface. By means of in situ scanning tunneling microscopy (STM), reversible phase transitions from a nanoporous low-temperature phase to a more densely packed high-temperature phase are observed. The occurrence of the phase transition and the respective transition temperature were found to depend on the type of solvent and solute concentration. Estimates of the entropic cost and enthalpic gain upon monolayer self-assembly suggest that coadsorption of solvent molecules within the cavities of the nanoporous structure renders this polymorph thermodynamically stable at low temperatures. At elevated temperatures, however, desorption of these relatively weakly bound solvent molecules destabilizes the nanoporous polymorph, and the densely packed polymorph becomes thermodynamically favored. Interestingly, the structural phase transition provides external control over the monolayer morphology and, for the system under discussion, results in an effective opening and closing of supramolecular nanopores in a two-dimensional molecular monolayer.
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thermodynamical equilibrium of binary supramolecular networks at the liquid Solid Interface
Journal of the American Chemical Society, 2008Co-Authors: Lorenz Kampschulte, Wolfgang M Heckl, Tova L Werblowsky, Ravuri S K Kishore, Michael Schmittel, Markus LackingerAbstract:Coadsorption of two different carboxylic acids, benzenetribenzoic acid and trimesic acid, was studied at the liquid-Solid Interface in two different solvents (heptanoic and nonanoic acid). Independent alteration of both concentrations in binary solutions resulted in six nondensely packed monolayer phases with different structures and stoichiometries, as revealed by means of scanning tunneling microscopy (STM). All of these structures are stabilized by intermolecular hydrogen bonding between the carboxylic acid functional groups. Moreover, phase transitions of the monolayer structures, accompanied by an alteration of the size and shape of cavity voids in the 2D molecular assembly, could be achieved by in situ dilution. The emergence of the various phases could be described by a simple thermodynamic model.
