Expression of Chirality in Physisorbed Monolayers Observed by Scanning Tunneling Microscopy

Feyter, Steven De; Iavicoli, Patrizia; Xu, Hong

doi:10.1002/9783527625345.ch7

Cited by 7 publications

(8 citation statements)

References 62 publications

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“…Because of the potential to serve in organic electronic devices, like light sensors or spin filters, , surface self-assembly of helicene films has attracted much interest recently. , In terms of chiral two-dimensional (2D) crystallization, they provide an interesting alternative to the commonly studied polar compounds like amino acids or long aliphatic chain compounds at the solid–liquid interface. − Figure presents several aspects discussed in this Account. We focus here on heptahelicene ([7]H, C 30 H 18 , Figure a), a compound that crystallizes (like [6]H, [8]H, and [9]H) as a conglomerate, , and its isomer dibenzopentahelicene (db[5]H; CAS, dibenzo[ f,j ]picene).…”

Section: A Model For Chiral Crystallization: Helicenes On Surfacesmentioning

confidence: 99%

“…The 2D self-assembly of enantiopure compounds on surfaces often leads to enantiomorphism of the adsorbate lattice. , That is, the lattice vectors of the molecular 2D crystals have an oblique tilt angle with respect to the underlying substrate crystal lattice. Molecular handedness is thereby transmitted by stereochemical recognition among the molecules as well as between molecules and specific surface sites.…”

Section: Transmission Of Chirality In Two Dimensions: From Single Mol...mentioning

confidence: 99%

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Stereochemical Recognition of Helicenes on Metal Surfaces

Ernst

2016

Acc. Chem. Res.

169

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The chiral recognition among biomolecules is fundamentally important for many processes of life, including the stereochemistry of evolution. Of special interest is chiral recognition during crystallization of racemates, when either homochiral recognition leads to a conglomerate of homochiral crystals or heterochiral recognition dominates resulting in a racemic compound. The complex nature of molecular recognition at the level of nucleation and crystal growth renders it difficult to understand and calls for manageable model systems. Notably, the approach of studying aggregation of molecules at surfaces under well-defined conditions includes the benefit of the availability of a multitude of highly sensitive investigation methods, of which scanning tunneling microscopy (STM) with its submolecular resolution is tremendously valuable. Heterogeneous nucleation at surfaces is strongly favored over homogeneous nucleation in solution; hence, surfaces are significantly involved in stereochemical recognition during crystallization. Helicenes are a fascinating class of chiral compounds with outstanding optical activity. These π-conjugated, ortho-fused, aromatic hydrocarbons are promising candidates for organic electronic devices such as sensors, circular dichroic photonics, liquid crystal displays or spin filters. But in particular the defined footprint of their terminal benzo rings on a surface makes them interesting for studying stereochemical recognition with different single crystalline surfaces and the impact this has, in turn, on intermolecular recognition. In this Account, we describe the self-assembly of helicenes on metal surfaces with the focus on stereochemical recognition in two-dimensional structures. Using the isomeric all-carbon helicenes, heptahelicene and dibenzohelicene as examples, different aggregation phenomena on different surfaces of single crystalline copper, silver, and gold are investigated. By means of STM different modes of transmission of molecular handedness from single molecules into extended two-dimensional supramolecular structures are identified. For the problem of racemate versus conglomerate crystallization, the impact of surface and molecular structure and their interplay are analyzed. This leads to detailed conclusions about the importance of the match of molecular and surface binding sites for long-range self-assembly. The absence of polar groups puts emphasis on van der Waals interaction and their maximization by steric overlap of molecular parts in enantiomeric and diastereomeric interactions. With STM as a manipulation tool, dimers are manually separated in order to analyze their chiral composition. And finally, new nonlinear cooperative effects induced by small enantiospecific bias are discovered that lead to single enantiomorphism in two-dimensional racemate crystals as well as in racemic multilayered films. By means of these model studies many details that govern chiral recognition at surfaces are rationalized.

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Section: A Model For Chiral Crystallization: Helicenes On Surfacesmentioning

confidence: 99%

Section: Transmission Of Chirality In Two Dimensions: From Single Mol...mentioning

confidence: 99%

Stereochemical Recognition of Helicenes on Metal Surfaces

Ernst

2016

Acc. Chem. Res.

169

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“…Photoresponsive molecular materials are at the forefront of the search for next-generation molecular optoelectronic devices. , The power of these devices which require immobilization on a solid surface are due to miniaturization down to the molecular level. − Even if many candidate molecules are well-understood in bulk 3D phases (i.e., in crystalline/amorphous solids or when dissolved in a liquid solution), excellent performance and reliability will require an accurate control and elucidation of molecular properties on a solid 2D-surface. , Indeed, adsorption may lead to new phenomena such as induction of chirality due to the suppression of some symmetry elements. − …”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, as the 2D solid surface could induce new phenomena previously unobserved in solution or in the solid state, − breakthroughs were uncovered such as chiral resolution of the closed forms, inelastic electron induced switching that goes through thermal routes, and reversal of stabilities of open and closed isomers on the metallic surface . Even then, the complexity afforded by diarylethenes over azobenzene due to the former’s larger and dissymmetric molecular structure and the higher number of degrees of freedom makes these systems challenging; the small difference between the geometry of the open and closed forms , also makes their identification by STM under UHV difficult.…”

Section: Introductionmentioning

confidence: 99%

Adsorption of Terarylenes on Ag(111) and NaCl(001)/Ag(111): A Scanning Tunneling Microscopy and Density Functional Theory Study

et al. 2018

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Photoswitching materials are building blocks of next generation optoelectronic devices which may require molecule deposition on a solid substrate. However, molecule properties change upon adsorption due to surface-molecule interactions and symmetry considerations. Scanning tunneling microscopy (STM) and density functional theory (DFT) offer techniques to address interactions of functional molecules down to the single-molecular level on solid substrates. In this paper, we present a combined STM and DFT study of a tert-butyl functionalized terarylene molecule on Ag(111) and NaCl(001)/Ag(111) at ∼5 K. tert-Butyl groups aided in identifying three conformations of the compound upon adsorption on the surface. DFT calculations showed that two of these conformations refer to different adsorption geometries of the trans conformation in the gas phase. The other was assigned to the nonreactive cis conformation. For the first time, this conformation was isolated and imaged at the single-molecular level. Calculations further showed that aside from the electronic structure of the molecule, methyl groups sticking out of the surface are the origin of bright spots observed on the STM. On NaCl(001)/Ag(111), only the trans conformation was found and the mapping of occupied and unoccupied states of terarylenes was accomplished for the first time.

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“…www.chemphyschem.org molecular interaction. [14][15][16] In the same way, the most popular plane groups of the 2D architectures are the groups p1, p2, pg and p2gg. These space groups allow objects of any shape to contact the largest numbers of neighboring objects.…”

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confidence: 99%

Growth of Textured Adenine Thin Films to Exhibit only Chiral Faces

et al. 2011

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The growth of adenine on Au(111) from the submonolayer up to several microns film thickness is studied by combining STM and surface X‐ray diffraction techniques. The study shows that adenine thin films are composed of highly textured crystallites with the reported α‐adenine crystal structure in such a way that they only exhibit (001)‐faces. Such faces, with chiral p2 symmetry planes, have an average size of 15 nm. Thus, the formed adenine films reported herein, which expose only chiral and biocompatible faces, might find applications such as enantioselective heterogeneous catalysts for the chemical and pharmaceutical industries.

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Expression of Chirality in Physisorbed Monolayers Observed by Scanning Tunneling Microscopy

Cited by 7 publications

References 62 publications

Stereochemical Recognition of Helicenes on Metal Surfaces

Stereochemical Recognition of Helicenes on Metal Surfaces

Adsorption of Terarylenes on Ag(111) and NaCl(001)/Ag(111): A Scanning Tunneling Microscopy and Density Functional Theory Study

Growth of Textured Adenine Thin Films to Exhibit only Chiral Faces

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