skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: ortho ‐Phenylene‐Based Macrocyclic Hydrocarbons Assembled Using Olefin Metathesis
While many foldamer systems reliably fold into well‐defined secondary structures, higher order structure remains a challenge. A simple strategy for the organization of folded subunits in space is to link them together within a macrocycle. Previous work has shown thato‐phenylenes can be co‐assembled with rod‐shaped linkers into twisted macrocycles, showing an interesting synergy between folding and thermodynamically controlled macrocyclization. In these systems the foldamer units were largely decoupled from each other both conformationally and electronically. Here, we show that hydrocarbon macrocycles, with very short ethenylene linkers, can be assembled fromo‐phenylenes using olefin metathesis. Characterization by NMR spectroscopy, X‐ray crystallography, and ab initio calculations shows that the products are approximately triangular trimer macrocycles with helicalo‐phenylene corners in a heterochiral configuration. Their photophysics are dominated by the 4,4'‐diphenylstilbene moieties, the longest conjugated segments, with further conjugation broken by the twisting of theo‐phenylenes.  more » « less
Award ID(s):
1608213 1904236
PAR ID:
10183171
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
European Journal of Organic Chemistry
Volume:
2020
Issue:
34
ISSN:
1434-193X
Format(s):
Medium: X Size: p. 5620-5625
Size(s):
p. 5620-5625
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, Chemical Science)
    null (Ed.)
    The self-assembly of foldamers into macrocycles is a simple approach to non-biological higher-order structure. Previous work on the co-assembly of ortho -phenylene foldamers with rod-shaped linkers has shown that folding and self-assembly affect each other; that is, the combination leads to new emergent behavior, such as access to otherwise unfavorable folding states. To this point this relationship has been passive. Here, we demonstrate control of self-assembly by manipulating the foldamers' conformational energy surfaces. A series of o -phenylene decamers and octamers have been assembled into macrocycles using imine condensation. Product distributions were analyzed by gel-permeation chromatography and molecular geometries extracted from a combination of NMR spectroscopy and computational chemistry. The assembly of o -phenylene decamers functionalized with alkoxy groups or hydrogens gives both [2 + 2] and [3 + 3] macrocycles. The mixture results from a subtle balance of entropic and enthalpic effects in these systems: the smaller [2 + 2] macrocycles are entropically favored but require the oligomer to misfold, whereas a perfectly folded decamer fits well within the larger [3 + 3] macrocycle that is entropically disfavored. Changing the substituents to fluoro groups, however, shifts assembly quantitatively to the [3 + 3] macrocycle products, even though the structural changes are well-removed from the functional groups directly participating in bond formation. The electron-withdrawing groups favor folding in these systems by strengthening arene–arene stacking interactions, increasing the enthalpic penalty to misfolding. The architectural changes are substantial even though the chemical perturbation is small: analogous o -phenylene octamers do not fit within macrocycles when perfectly folded, and quantitatively misfold to give small macrocycles regardless of substitution. Taken together, these results represent both a high level of structural control in structurally complex foldamer systems and the demonstration of large-amplitude structural changes as a consequence of a small structural effects. 
    more » « less
  2. ; ; (, Chemistry – A European Journal)
    Foldamers, oligomers that adopt well‐defined conformations, represent an efficient strategy toward nanoscale structural complexity. While most foldamers fold into helices, many abiotic foldamers are built from achiral repeat units and therefore do not have a preferred twist sense. Their handedness can, however, be controlled by attaching groups with chirality centers to the foldamer backbone. This process allows chiral information from readily available compounds to be amplified into larger‐scale structural asymmetry and translated into functional behavior. This review describes mechanisms whereby the point chirality of chiral “controller” groups directs foldamer twist sense. We highlight examples of aromatic oligoamides, oligohydrazides, oligoindoles, oligo(ortho‐phenylenes), oligooxymethylenes, and oligo(aminoisobutyric acids), examining cases where the controller groups are attached at either the helices’ termini or sides. Our emphasis is on applying intuitive concepts from conformational analysis and, where appropriate, computational modeling of small substructures. In each case, we consider first short‐range interactions that orient the controller group relative to its direct point of attachment to the foldamer, and then its long‐range interactions with more‐distant parts of the oligomer. Together, these interactions allow the twist sense to be predicted (or at least rationalized). Understanding these mechanisms should facilitate the design of systems with dynamic control over helicity. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, Nature Communications)
    Abstract Macrocycles are unique molecular structures extensively used in the design of catalysts, therapeutics and supramolecular assemblies. Among all reactions reported to date, systems that can produce macrocycles in high yield under high reaction concentrations are rare. Here we report the use of dynamic hindered urea bond (HUB) for the construction of urea macrocycles with very high efficiency. Mixing of equal molar diisocyanate and hindered diamine leads to formation of macrocycles with discrete structures in nearly quantitative yields under high concentration of reactants. The bulkyN-tert-butyl plays key roles to facilitate the formation of macrocycles, providing not only the kinetic control due to the formation of the cyclization-promotingcisC = O/tert-butyl conformation, but also possibly the thermodynamic stabilization of macrocycles with weak association interactions. The bulkyN-tert-butyl can be readily removed by acid to eliminate the dynamicity of HUB and stabilize the macrocycle structures. 
    more » « less
  4. ; ; ; ; (, Macromolecular Rapid Communications)
    Abstract ortho‐Phenylenes are one of the simplest classes of aromatic foldamers, adopting helical geometries because of aromatic stacking interactions. The folding and misfolding ofortho‐phenylenes are slow on the NMR timescale at or below room temperature, allowing detection of folding states using1H NMR spectroscopy. Herein, anortho‐phenylene hexamer is coupled with a RAFT chain transfer agent (CTA) on each repeat unit. A variety of acrylic monomers are polymerized onto the CTA‐functionalizedortho‐phenylene using PET‐RAFT to yield functionalized star polymers withortho‐phenylene cores. The steric bulk of the acrylate monomer units as well as the chain length of each arm of the star polymer is varied.1H NMR spectroscopy shows that the folding of theortho‐phenylenes do not vary, providing a robust helical core for star polymer systems. 
    more » « less
  5. ; ; ; ; ; ; ; (, The Journal of Organic Chemistry)
    Despite their structural similarities, ortho-phenylenes and 2,3-quinoxalinylenes (i.e., poly(quinoxaline-2,3-diyl)s), well known as foldamers and helical polymers, respectively, exhibit distinctly different conformational behavior. o-Phenylenes tend to fold into compact helices with every fourth ring stacked, whereas 2,3-quinoxalinylenes favor extended helices with no backbone stacking. To understand this difference, we have studied short o-arylenes with different sequences of benzene and pyrazine units. Through a combination of crystallography, variable-temperature NMR spectroscopy, and DFT calculations, we find that pyrazines favor extended helical conformations as a result of two effects. First, within an o-arylene architecture, pyrazines experience weaker arene–arene interactions. Cofacial packing of the rings is therefore less favorable. Second, bipyrazine units lead to an increase in vibrational entropy for extended conformers. Consequently, at higher temperatures (including room temperature), extended helices are favored for the heterocycle-containing systems. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email