Quadruple[6]Helicene Featuring Pyrene Core: Unraveling Contorted Aromatic Core with Larger Effective Conjugation.
Christopher Wallerius1, Otgonbayar Erdene-Ochir1, Eva Van Doeselar1
1Department of Chemistry, University of Cologne, Cologne 50939, Germany.
Precision Chemistry
|October 30, 2024
Summary
Researchers synthesized a novel quadruple[6]helicene with a pyrene core, controlling its twist for unique optical properties. This work introduces new strategies for designing complex aromatic molecules and reveals self-assembly into chiral nanosheets.
Area of Science:
- Organic Chemistry
- Materials Science
- Supramolecular Chemistry
Background:
- Multiple helicenes possess unique twisted aromatic cores, offering diverse properties and topologies.
- Modifying these aromatic cores is key to developing novel helicene derivatives with tailored characteristics.
Purpose of the Study:
- To report the synthesis of a quadruple[6]helicene incorporating a pyrene aromatic core.
- To investigate the influence of axial extension and contortion on the photophysical properties of multiple helicenes.
- To explore novel self-assembly behaviors of synthesized helicene derivatives.
Main Methods:
- Synthesis via annulative π-extension and Scholl reactions.
- Control over the degree of aromatic core contortion through axial extension.
- Photophysical characterization including UV-Vis spectroscopy.
- Quantum chemical calculations to analyze electronic properties (HOMO/LUMO levels).
Main Results:
- Successful synthesis of a quadruple[6]helicene with a pyrene core.
- Demonstrated control over molecular contortion from nearly flat to highly twisted.
- Observed a significant 0.49 eV red-shift in quadruple[6]helicene compared to quadruple[4]helicenes, attributed to π-extension and enhanced twisting.
- Quantum chemical calculations confirmed that pyrene core contortion modulates HOMO/LUMO energy levels.
- Discovered the spontaneous formation of one-molecule-thick supramolecular homochiral nanosheets via enantiomeric self-interlocking in single crystals.
Conclusions:
- The contortion of the pyrene core in quadruple[6]helicene is a crucial factor in tuning electronic properties, offering an alternative to simple π-backbone enlargement.
- The study presents a novel synthetic route to complex helicenes and highlights their potential in creating advanced materials.
- The unexpected formation of homochiral nanosheets reveals a rare and intriguing supramolecular assembly motif for multiple helicenes.
Related Concept Videos
01:18Aromatic Hydrocarbon Cations: Structural Overview
2.8K
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
Removing one hydrogen from the intervening CH2 group...
2.8K
01:13Five-Membered Heterocyclic Aromatic Compounds: Overview
3.8K
Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom,...
3.8K
01:20Criteria for Aromaticity and the Hückel 4n + 2 Rule
10.3K
Like benzene, cyclobutadiene and cyclooctatetraene are cyclic compounds with alternate single and double bonds. However, their chemical behavior differs from benzene, as they are unstable and not aromatic. So, what are the structural characteristics of unsaturated compounds categorized as aromatic?
For the first time, Eric Hückel, a German chemical physicist, derived a set of structural features for a compound to be classified as aromatic. This is now known as...
For the first time, Eric Hückel, a German chemical physicist, derived a set of structural features for a compound to be classified as aromatic. This is now known as...
10.3K
01:18Aromatic Hydrocarbon Anions: Structural Overview
2.7K
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous...
Due to the absence of continuous...
2.7K
01:18Frost Circles for Different Conjugated Systems
2.7K
The inscribed polygon method is consistent with Hückel’s 4n + 2 rule and helps to learn whether the given cyclic compound is aromatic or not. The compound is stable and aromatic if every bonding molecular orbital (MO) is completely filled with a pair of electrons. However, if the non-bonding or antibonding orbitals are filled with electrons, the compound is unstable and not aromatic. Consider the Frost circle diagrams for cycloalkenes containing 4 to 8 carbons.
2.7K
01:27¹H NMR: Long-Range Coupling
1.7K
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
1.7K