16 research outputs found
A Scanning Tunneling Microscopy Study on Surface-Supported Imine-Based Covalent Organic Frameworks: a New Design for Robust 2D Materials.
Insights into dynamic covalent chemistry at surfaces
The potential of surface confined self-assembly to influence the chemical equilibrium of Schiff base formation and bias the yield and distribution of reaction products is exploredcrosscheck: This document is CrossCheck deposited
related_data: Supplementary Information
copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal
copyright_licence: The accepted version of this article will be made freely available in the Chemical Sciences Article Repository after a 12 month embargo period
history: Received 19 August 2015; Accepted 11 September 2015; Advance Article published 25 September 2015; Version of Record published 3 November 2015status: publishe
Diazadithia[7] helicenes: synthetic exploration, solid state structure and properties
Diazadithia[7]helicenes were synthesized from the readily available building block ethyl 7-chloro-8-formylthieno[3,2-f]quinoline-2-carboxylate by a Wittig reaction-photocyclization strategy. The helicene core was functionalized by nucleophilic aromatic substitution with a variety of nucleophiles (e.g., O-, N-, and C-centered) and palladium-catalyzed reactions such as Suzuki coupling and Buchwald-Hartwig amination. Racemization studies confirmed that the enantiopure forms of these [7]helicenes are conformationally stable compared to their lower analogues. The solid-state structures of the novel diazadithia[7]helicenes were determined by single-crystal X-ray diffraction. The crystal structures of these azathia[7]helicenes show columnar stacking in antiparallel fashion. The HOMO-LUMO gaps of the new compounds were determined on the basis of electrochemical and optical measurements.status: publishe
Synthesis, Functionalization, and Optical Properties of Chiral Carbazole-Based Diaza[6]helicenes
In
the present study, carbazole-based diaza[6]helicenes were synthesized
utilizing versatile quinoline and 9-(2-ethylhexyl)-2,7-dimethoxycarbazole-3-carbaldehyde
building blocks via the Wittig reaction–photocyclization strategy.
The presence of bifunctional units comprising electrophilic chloroquinoline
and electron-rich carbazole has opened up new opportunities. The chloro
group was substituted with a chiral amine, allowing diastereomeric
separation, and the chiral forms were monofunctionalized via electrophilic
substitution on the carbazole unit. Postcyclization functionalization
via substituting the carbazole unit provides a platform for the synthesis
of chiral functionalized materials with potential application in fields
such as asymmetric synthesis and organic electronics. The configuration
of the diaza[6]helicene diastereomers was demonstrated by time-dependent
density functional theory (TD-DFT) calculations. Furthermore, on the
basis of the DFT calculations of the HOMO–LUMO energy levels
of the chiral forms, these compounds can be potentially of interest
as hole-transporting compound
Halogenated building blocks for 2D crystal engineering on solid surfaces: lessons from hydrogen bonding
Halogen bonding has emerged as a promising tool in two-dimensional (2D) crystal engineering. Since halogen bonds are similar to hydrogen bonds in a number of aspects, the existing knowledge of hydrogen bonded systems can be applied to halogenated systems. Here we evaluate the applicability of a retrosynthetic approach based on topological similarity between hydrogen and halogen bonds to obtain predictable halogen bonded networks. The self-assembly of 1,3-dibromo-5-alkoxybenzene derivatives was studied in analogy with well-explored alkoxy isophthalic acids using a combination of experimental and theoretical tools. Scanning tunneling microscopy (STM) characterization of the networks formed at the liquid-graphite interface revealed that while the retrosynthetic approach works at the level of small clusters of molecules within the 2D network, the overall structure of the network deviates from the anticipated structure. The monolayers consist of fractured rows of halogen-bonded modules instead of the expected continuous lamellar structure. Each module consists of a discrete number of halogen-bonded molecules. The interactions responsible for the stabilization of halogen bonded dimers are delineated through detailed density functional theory (DFT) calculations coupled with natural bonding orbitals (NBO) and perturbation analysis. A modified force field that includes an extra charged site to imitate the σ hole on the halogen atom was developed and applied to extract total potential energies of the anticipated and observed networks. Plausible reasons for the deviation from the anticipated structure are discussed. Finally, a modified molecular design that allows successful application of the hydrogen bond-halogen bond analogy was tested experimentally.status: publishe
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Halogenated building blocks for 2D crystal engineering on solid surfaces: lessons from hydrogen bonding.
Halogen bonding has emerged as a promising tool in two-dimensional (2D) crystal engineering. Since halogen bonds are similar to hydrogen bonds in a number of aspects, the existing knowledge of hydrogen bonded systems can be applied to halogenated systems. Here we evaluate the applicability of a retrosynthetic approach based on topological similarity between hydrogen and halogen bonds to obtain predictable halogen bonded networks. The self-assembly of 1,3-dibromo-5-alkoxybenzene derivatives was studied in analogy with well-explored alkoxy isophthalic acids using a combination of experimental and theoretical tools. Scanning tunneling microscopy (STM) characterization of the networks formed at the liquid-graphite interface revealed that while the retrosynthetic approach works at the level of small clusters of molecules within the 2D network, the overall structure of the network deviates from the anticipated structure. The monolayers consist of fractured rows of halogen-bonded modules instead of the expected continuous lamellar structure. Each module consists of a discrete number of halogen-bonded molecules. The interactions responsible for the stabilization of halogen bonded dimers are delineated through detailed density functional theory (DFT) calculations coupled with natural bonding orbitals (NBO) and perturbation analysis. A modified force field that includes an extra charged site to imitate the σ hole on the halogen atom was developed and applied to extract total potential energies of the anticipated and observed networks. Plausible reasons for the deviation from the anticipated structure are discussed. Finally, a modified molecular design that allows successful application of the hydrogen bond-halogen bond analogy was tested experimentally
Hierarchical self-assembly of enantiopure and racemic helicenes at the liquid/solid interface: from 2D to 3D
The performance of organic nanostructures is closely related to the organization of the functional molecules. Frequently, molecular chirality plays a central role in the way molecules assemble at the supramolecular level. Herein we report the hierarchical self-assembly of benzo-fused tetrathia[7]helicenes on solid surfaces, from a single surface-bound molecule to well-defined microstructures, using a combination of various characterization techniques assisted by molecular modeling simulations. Similarities as well as discrepancies are revealed between homochiral and heterochiral aggregations by monitoring the hierarchical nucleation of helicenes on surfaces, where the impact of enantiopurity, concentration and adsorbate-substrate interaction on molecular organization are disclosed.status: publishe
Synthesis and Structural Elucidation of Diversely Functionalized 5,10-Diaza[5]Helicenes
Diversely functionalized diaza[5]helicenes have been
synthesized
starting from 6,9-dichloro-5,10-diaza[5]helicene, which was prepared
from a readily available quinoline building block via Wittig reaction
followed by photochemical electrocyclization. The helicene skeleton
was substituted by a variety of O-, S-, N-, and C-centered nucleophiles
using nucleophilic aromatic substitution reactions and palladium-catalyzed
reactions like Suzuki coupling and Buchwald–Hartwig aminations.
We have determined, using X-ray single-crystal diffraction, the crystal
structures of the chloro- and methoxy-substituted diaza[5]helicenes.
A resolution strategy based on diastereomeric separation by substitution
of the dichloro derivative with a chiral amine has been shown