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Circumcoronene, a hexagonal graphene fragment with six zigzag edges, has been the focus of theoretical studies for many years, but its synthesis in solution has remained a challenge. In this study, we present a facile method for synthesizing three derivatives of circumcoronene using Brønsted/Lewis acid‐mediated cyclization of vinyl ether or alkyne. Their structures were confirmed through X‐ray crystallographic analysis. Bond length analysis, NMR measurement, and theoretical calculations showed that circumcoronene mostly follows Clar's bonding model and exhibits dominant local aromaticity. Its absorption and emission spectra are similar to those of the smaller hexagonal coronene due to its six‐fold symmetry. [ABSTRACT FROM AUTHOR]

Circumcoronene, a hexagonal graphene fragment with six zigzag edges, has been the focus of theoretical studies for many years, but its synthesis in solution has remained a challenge. In this study, we present a facile method for synthesizing three derivatives of circumcoronene using Brønsted/Lewis acid‐mediated cyclization of vinyl ether or alkyne. Their structures were confirmed through X‐ray crystallographic analysis. Bond length analysis, NMR measurement, and theoretical calculations showed that circumcoronene mostly follows Clar's bonding model and exhibits dominant local aromaticity. Its absorption and emission spectra are similar to those of the smaller hexagonal coronene due to its six‐fold symmetry. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) with a one‐dimensional (1D), ribbon‐like structure have the potential to serve as both model compounds for corresponding graphene nanoribbons (GNRs) and as materials for optoelectronics applications. However, synthesizing molecules of this type with extended π‐conjugation presents a significant challenge. In this study, we present a straightforward synthetic method for a series of bis‐peri‐dinaphtho‐rylene molecules, wherein the peri‐positions of perylene, quaterrylene, and hexarylene are fused with naphtho‐units. These molecules were efficiently synthesized primarily through intramolecular or intermolecular radical coupling of in situ generated organic radical species. Their structures were confirmed using X‐ray crystallographic analysis, which also revealed a slightly bent geometry due to the incorporation of a cyclopentadiene ring at the bay regions of the rylene backbones. Bond lengh analysis and theoretical calculations indicate that their electronic structures resemble pyrenacenes more than quinoidal rylenes. That is, the aromatic sextets are predominantly localized along the long axis of the skeletones. As the chain length increases, these molecules exhibit enhanced electronic absorption with a bathochromic shift, and multiple amphoteric redox waves. This study introduces a novel synthetic approach for generating 1D extended PAHs and GNRs, along with their structure‐dependent electronic properties. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) with a one‐dimensional (1D), ribbon‐like structure have the potential to serve as both model compounds for corresponding graphene nanoribbons (GNRs) and as materials for optoelectronics applications. However, synthesizing molecules of this type with extended π‐conjugation presents a significant challenge. In this study, we present a straightforward synthetic method for a series of bis‐peri‐dinaphtho‐rylene molecules, wherein the peri‐positions of perylene, quaterrylene, and hexarylene are fused with naphtho‐units. These molecules were efficiently synthesized primarily through intramolecular or intermolecular radical coupling of in situ generated organic radical species. Their structures were confirmed using X‐ray crystallographic analysis, which also revealed a slightly bent geometry due to the incorporation of a cyclopentadiene ring at the bay regions of the rylene backbones. Bond lengh analysis and theoretical calculations indicate that their electronic structures resemble pyrenacenes more than quinoidal rylenes. That is, the aromatic sextets are predominantly localized along the long axis of the skeletones. As the chain length increases, these molecules exhibit enhanced electronic absorption with a bathochromic shift, and multiple amphoteric redox waves. This study introduces a novel synthetic approach for generating 1D extended PAHs and GNRs, along with their structure‐dependent electronic properties. [ABSTRACT FROM AUTHOR]

Circumacenes (CAs) are a distinctive type of benzenoid polycyclic aromatic hydrocarbons where an acene unit is completely enclosed by a layer of outer fused benzene rings. Despite their unique structures, the synthesis of CAs is challenging, and until recently, the largest CA molecule synthesized was circumanthracene. In this study, we report the successful synthesis of an extended circumpentacene derivative 1, which represents the largest CA molecule synthesized to date. Its structure was confirmed by X‐ray crystallographic analysis and its electronic properties were systematically investigated by both experiments and theoretical calculations. It shows a unique open‐shell diradical character due to the existence of extended zigzag edges, with a moderate diradical character index (y0=39.7 %) and a small singlet‐triplet energy gap (ΔES‐T=−4.47 kcal/mol). It exhibits a dominant local aromatic character with π‐electrons delocalized in the individual aromatic sextet rings. It has a small HOMO–LUMO energy gap and displays amphoteric redox behavior. The electronic structures of its dication and dianion can be considered as doubly charged structures in which two coronene units are fused with a central aromatic benzene ring. This study provides a new route toward stable multizigzag‐edged graphene‐like molecules with open‐shell di/polyradical character. [ABSTRACT FROM AUTHOR]

Circumacenes (CAs) are a distinctive type of benzenoid polycyclic aromatic hydrocarbons where an acene unit is completely enclosed by a layer of outer fused benzene rings. Despite their unique structures, the synthesis of CAs is challenging, and until recently, the largest CA molecule synthesized was circumanthracene. In this study, we report the successful synthesis of an extended circumpentacene derivative 1, which represents the largest CA molecule synthesized to date. Its structure was confirmed by X‐ray crystallographic analysis and its electronic properties were systematically investigated by both experiments and theoretical calculations. It shows a unique open‐shell diradical character due to the existence of extended zigzag edges, with a moderate diradical character index (y0=39.7 %) and a small singlet‐triplet energy gap (ΔES‐T=−4.47 kcal/mol). It exhibits a dominant local aromatic character with π‐electrons delocalized in the individual aromatic sextet rings. It has a small HOMO–LUMO energy gap and displays amphoteric redox behavior. The electronic structures of its dication and dianion can be considered as doubly charged structures in which two coronene units are fused with a central aromatic benzene ring. This study provides a new route toward stable multizigzag‐edged graphene‐like molecules with open‐shell di/polyradical character. [ABSTRACT FROM AUTHOR]

A planar dibenzo‐peri‐hexacene derivative (2) was synthesized via FeCl3‐mediated Scholl reaction from a cyclopenta‐fused perylene (CP) based polyphenylene precursor (1). However, an unexpected octagon‐containing, negatively curved molecule (3) was obtained in nearly quantitative yield when 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and methanesulfonic acid (MeSO3H) were used. Similar results were observed when two smaller‐sized precursors containing one (4) or two CP units (5) were tested. X‐ray crystallographic analysis also revealed that there is no close π–π stacking between neighboring π‐conjugated skeletons. DFT calculations suggest a radical cation mechanism in the presence of FeCl3 while an arenium ion pathway for the DDQ/MeSO3H mediated Scholl reaction, which can well explain the selective formation of hexagons and octagons under different conditions. The obtained compounds showed tunable optical and electrochemical properties. [ABSTRACT FROM AUTHOR]

A planar dibenzo‐peri‐hexacene derivative (2) was synthesized via FeCl3‐mediated Scholl reaction from a cyclopenta‐fused perylene (CP) based polyphenylene precursor (1). However, an unexpected octagon‐containing, negatively curved molecule (3) was obtained in nearly quantitative yield when 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and methanesulfonic acid (MeSO3H) were used. Similar results were observed when two smaller‐sized precursors containing one (4) or two CP units (5) were tested. X‐ray crystallographic analysis also revealed that there is no close π–π stacking between neighboring π‐conjugated skeletons. DFT calculations suggest a radical cation mechanism in the presence of FeCl3 while an arenium ion pathway for the DDQ/MeSO3H mediated Scholl reaction, which can well explain the selective formation of hexagons and octagons under different conditions. The obtained compounds showed tunable optical and electrochemical properties. [ABSTRACT FROM AUTHOR]