Direct Determination of the Chirality of Organic Molecules by Scanning Tunneling Microscopy

Fang, Hongbin; Giancarlo, Leanna C.; Flynn, George W.

doi:10.1021/jp981960z

Cited by 109 publications

(165 citation statements)

References 15 publications

(38 reference statements)

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“…[12][13][14][15] In some cases, indications of spontaneous chiral segregation of racemic films have been reported. [16][17][18][19] When the substrate atomic order is affected, even chiral restructuring may occur. 20 Finally, chirality may be expressed at the supramolecular level in discrete molecular assemblies at surfaces which are stabilized by noncovalent bonds.…”

Section: Introductionmentioning

confidence: 99%

Stereochemical Effects in Supramolecular Self-Assembly at Surfaces: 1-D versus 2-D Enantiomorphic Ordering for PVBA and PEBA on Ag(111)

et al. 2002

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Abstract:We present investigations on noncovalent bonding and supramolecular self-assembly of two related molecular building blocks at a noble metal surface: 4-[trans-2-(pyrid-4-yl-vinyl)]benzoic acid (PVBA) and 4-[(pyrid-4-yl-ethynyl)]benzoic acid (PEBA). These rigid, rodlike molecules comprising the same complementary moieties for hydrogen bond formation are comparable in shape and size. For PVBA, the ethenylene moiety accounts for two-dimensional (2-D) chirality upon confinement to a surface; PEBA is linear and thus 2-D achiral. Molecular films were deposited on a Ag(111) surface by organic molecular beam epitaxy and characterized by scanning tunneling microscopy. At low temperatures (around 150 K), both species form irregular networks of flat lying molecules linked via their endgroups in a diffusion-limited aggregation process. In the absence of kinetic limitations (adsorption or annealing at room temperature), hydrogen-bonded supramolecular assemblies form which are markedly different. With PVBA, enantiomorphic twin chains in two mirror-symmetric species running along a high-symmetry direction of the substrate lattice form by diastereoselective self-assembly of one enantiomer. The chirality signature is strictly correlated between neighboring twin chains. Enantiopure one-dimensional (1-D) supramolecular nanogratings with tunable periodicity evolve at intermediate coverages, reflecting chiral resolution in micrometer domains. In contrast, PEBA assembles in 2-D hydrogen-bonded islands, which are enantiomorphic because of the orientation of the supramolecular arrangements along low-symmetry directions of the substrate. Thus, for PVBA, chiral molecules form 1-D enantiomorphic supramolecular structures because of mesoscopic resolution of a 2-D chiral species, whereas with PEBA, the packing of an achiral species causes 2-D enantiomorphic arrangements. Model simulations of supramolecular ordering provide a deeper understanding of the stability of these systems.

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Section: Introductionmentioning

confidence: 99%

Stereochemical Effects in Supramolecular Self-Assembly at Surfaces: 1-D versus 2-D Enantiomorphic Ordering for PVBA and PEBA on Ag(111)

et al. 2002

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“…Scanning tunnelling microscopy (STM) imaging at submolecular resolution has offered a great deal of information on the local structure, chiral organization, separation and recognition of both intrinsically chiral and prochiral molecules on surfaces [14][15][16][17][18][19] . Interestingly, experiments have revealed that the enantiomer units may be intermediate chiral assemblies of smaller achiral molecules 20 , and may even form on mirror symmetric (non-chiral) substrates such as high-symmetry noble metal surfaces 21 .…”

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confidence: 99%

Stereoselectivity and electrostatics in charge-transfer Mn- and Cs-TCNQ4 networks on Ag(100)

et al. 2012

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Controlling supramolecular self-assembly is a fundamental step towards molecular nanofabrication, which involves a formidable reverse engineering problem. It is known that a variety of structures are efficiently obtained by assembling appropriate organic molecules and transition metal atoms on well-defined substrates. Here we show that alkali atoms bring in new functionalities compared with transition metal atoms because of the interplay of local chemical bonding and long-range forces. using atomic-resolution microscopy and theoretical modelling, we investigate the assembly of alkali (Cs) and transition metals (mn) co-adsorbed with 7,7,8,8-tetracyanoquinodimethane (TCnQ) molecules, forming chiral superstructures on Ag(100). Whereas mn-TCnQ 4 domains are achiral, Cs-TCnQ 4 forms chiral islands. The specific behaviour is traced back to the different nature of the Cs-and mn-TCnQ bonding, opening a novel route for the chiral design of supramolecular architectures. moreover, alkali atoms provide a means to modify the adlayer electrostatic properties, which is important for the design of metal-organic interfaces.

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“…The occurrence of chiral preference may be an important step in the heterogeneous catalytic conversion of prochiral reagents into one of possible optical isomers. Such enantioselectivity is usually induced by adsorbing chiral molecules onto catalytically active surfaces [4]. This is why a characterization of chiral centers in adsorbed molecules is desirable.…”

mentioning

confidence: 99%

Atom-Specific Identification of Adsorbed Chiral Molecules by Photoemission

et al. 2005

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The study of chiral adsorbed molecules is important for an analysis of enantioselectivity in heterogeneous catalysis. Here we show that such molecules can be identified through circular dichroism in corelevel photoemission arising from the chiral carbon atoms in stereoisomers of 2,3-butanediol molecules adsorbed on Si(100), using circularly polarized x rays. The asymmetry in the carbon 1s intensity excited by right and left circularly polarized light is readily observed, and changes sign with the helicity of the radiation or handedness of the enantiomers; it is absent in the achiral form of the molecule. This observation demonstrates the possibility of determining molecular chirality in the adsorbed phase.

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Direct Determination of the Chirality of Organic Molecules by Scanning Tunneling Microscopy

Cited by 109 publications

References 15 publications

Stereochemical Effects in Supramolecular Self-Assembly at Surfaces: 1-D versus 2-D Enantiomorphic Ordering for PVBA and PEBA on Ag(111)

Stereochemical Effects in Supramolecular Self-Assembly at Surfaces: 1-D versus 2-D Enantiomorphic Ordering for PVBA and PEBA on Ag(111)

Stereoselectivity and electrostatics in charge-transfer Mn- and Cs-TCNQ4 networks on Ag(100)

Atom-Specific Identification of Adsorbed Chiral Molecules by Photoemission

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