acene
{{short description|Class of chemical compounds}}
{{distinguish|text = the class of hydronitrogens known as "azenes"}}
File:Acenes general structure.svg
In organic chemistry, the acenes or polyacenes are a class of organic compounds and polycyclic aromatic hydrocarbons made up of benzene ({{chem2|C6H6}}) rings which have been linearly fused. They follow the general molecular formula {{chem2|C_{4n+2}H_{2n+4} }}.
The larger representatives have potential interest in optoelectronic applications and are actively researched in chemistry and electrical engineering. Pentacene has been incorporated into organic field-effect transistors, reaching charge carrier mobilities as high as 5 cm2/Vs.
The first 5 unsubstituted members are listed in the following table:
| class="wikitable"
! Name ! Number of rings |
| Anthracene
| 3 | {{chem2|C14H10}} | 155px |
| Tetracene
| 4 | {{chem2|C18H12}} |
| Pentacene
| 5 | {{chem2|C22H14}} |
| Hexacene
| 6 | {{chem2|C26H16}} |
| Heptacene
| 7 | {{chem2|C30H18}} |
Hexacene is not stable in air, and dimerises upon isolation. Heptacene (and larger acenes) is very reactive and has only been isolated in a matrix. However, bis(trialkylsilylethynylated) versions of heptacene have been isolated as crystalline solids.
Larger acenes
Due to their increased conjugation length the larger acenes are also studied. Theoretically, a number of reports are available on longer chains using density functional methods. They are also building blocks for nanotubes and graphene. Unsubstituted octacene (n=8) and nonacene (n=9) have been detected in matrix isolation. The first reports of stable nonacene derivatives claimed that due to the electronic effects of the thioaryl substituents the compound is not a diradical but a closed-shell compound with the lowest HOMO-LUMO gap reported for any acene, an observation in violation of Kasha's rule. Subsequent work by others on different derivatives included crystal structures, with no such violations. The on-surface synthesis and characterization of unsubstituted, parent nonacene (n=9) and decacene (n=10) have been reported. In 2020, scientists reported about the creation of dodecacene (n=12){{Cite journal|last1=Eisenhut|first1=Frank|last2=Kühne|first2=Tim|last3=García|first3=Fátima|last4=Fernández|first4=Saleta|last5=Guitián|first5=Enrique|last6=Pérez|first6=Dolores|last7=Trinquier|first7=Georges|last8=Cuniberti|first8=Gianaurelio|last9=Joachim|first9=Christian|last10=Peña|first10=Diego|last11=Moresco|first11=Francesca|date=2020-01-28|title=Dodecacene Generated on Surface: Reopening of the Energy Gap|url=https://pubs.acs.org/doi/10.1021/acsnano.9b08456|journal=ACS Nano|language=en|volume=14|issue=1|pages=1011–1017|doi=10.1021/acsnano.9b08456|pmid=31829618 |issn=1936-0851|arxiv=2004.02517|s2cid=209341741 }} for the first time. Four years later, in the beginning of 2024, Ruan et al. succeeded in synthesizing unsubstitued tridecacene (n=13) on a (111)-gold surface. The acene was characterized by STM- and STS-measurements. {{Cite journal |last=Ruan |first=Zilin |last2=Schramm |first2=Jakob |last3=Bauer |first3=John B. |last4=Naumann |first4=Tim |last5=Bettinger |first5=Holger F. |last6=Tonner-Zech |first6=Ralf |last7=Gottfried |first7=J. Michael |date=2024-01-12 |title=Synthesis of Tridecacene by Multistep Single-Molecule Manipulation |url=https://pubs.acs.org/doi/10.1021/jacs.3c09392 |journal=Journal of the American Chemical Society |language=en |doi=10.1021/jacs.3c09392 |issn=0002-7863|doi-access=free |pmc=10870776 }}
Related compounds
The acene series have the consecutive rings linked in a linear chain, but other chain linkages are possible. The phenacenes have a zig-zag structure and the helicenes have a helical structure.
File:Heptacene 200.svg|Heptacene
File:7-phenacene.svg|[7]Phenacene
File:M-heptahelicene.svg|M-heptahelicene
Benz[a]anthracene, an isomer of tetracene, has three rings connected in a line and one ring connected at an angle.
References
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{{GoldBookRef|file=A00061|title=acenes}}
{{doi|10.1351/PAC-CON-09-10-29}}
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{{Hydrocarbons}}
{{PAHs}}
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