Acene

In organic chemistry, the acenes or polyacenes are a class of organic compounds and polycyclic aromatic hydrocarbons made up of benzene (C6H6) rings which have been linearly fused.[1][2] They follow the general molecular formula C4n+2H2n+4.

Not to be confused with the class of hydronitrogens known as "azenes".
The general structural formula for acenes

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:

Name Number of rings Molecular formula Structural formula
Anthracene 3 C14H10
Tetracene 4 C18H12
Pentacene 5 C22H14
Hexacene 6 C26H16
Heptacene 7 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.[3]

Larger acenes

Due to their increased conjugation length the larger acenes are also studied.[4] Theoretically, a number of reports are available on longer chains using density functional methods.[5][6] They are also building blocks for nanotubes and graphene. Unsubstituted octacene (n=8) and nonacene (n=9)[7] 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,[8] an observation in violation of Kasha's rule. Subsequent work by others on different derivatives included crystal structures, with no such violations.[9] The on-surface synthesis and characterization of unsubstituted, parent nonacene (n=9)[10] and decacene (n=10)[11] have been reported. In 2020, scientists reported about the creation of dodecacene (n=12)[12] for the first time.

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.

  • Macromolecular forms consisting of seven fused benzene rings
  • Heptacene
    Heptacene
  • [7]Phenacene
    [7]Phenacene
  • M-heptahelicene
    M-heptahelicene

Benz[a]anthracene, an isomer of tetracene, has three rings connected in a line and one ring connected at an angle.

References
  1. IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "acenes". doi:10.1351/goldbook.A00061
  2. Electronic structure of higher acenes and polyacene: The perspective developed by theoretical analyses Holger F. Bettinger Pure Appl. Chem., Vol. 82, No. 4, pp. 905–915, 2010. doi:10.1351/PAC-CON-09-10-29
  3. Anthony, John E. (2008). "The Larger Acenes: Versatile Organic Semiconductors". Angewandte Chemie International Edition. 47 (3): 452–83. doi:10.1002/anie.200604045. PMID 18046697.
  4. Zade, Sanjio S.; Bendikov, Michael (2010). "Heptacene and Beyond: the Longest Characterized Acenes". Angewandte Chemie International Edition. 49 (24): 4012–5. doi:10.1002/anie.200906002. PMID 20468014.
  5. Wu, Chun-Shian; Chai, Jeng-Da (2015-05-12). "Electronic Properties of Zigzag Graphene Nanoribbons Studied by TAO-DFT". Journal of Chemical Theory and Computation. 11 (5): 2003–2011. doi:10.1021/ct500999m. ISSN 1549-9618. PMID 26894252.
  6. Seenithurai, Sonai; Chai, Jeng-Da (2016-09-09). "Effect of Li Adsorption on the Electronic and Hydrogen Storage Properties of Acenes: A Dispersion-Corrected TAO-DFT Study". Scientific Reports. 6 (1): 33081. arXiv:1606.03489. Bibcode:2016NatSR...633081S. doi:10.1038/srep33081. ISSN 2045-2322. PMC 5016802. PMID 27609626.
  7. Tönshoff, Christina; Bettinger, Holger F. (2010). "Photogeneration of Octacene and Nonacene". Angewandte Chemie International Edition. 49 (24): 4125–8. doi:10.1002/anie.200906355. PMID 20432492.
  8. Kaur, Irvinder; Jazdzyk, Mikael; Stein, Nathan N.; Prusevich, Polina; Miller, Glen P. (2010). "Design, Synthesis, and Characterization of a Persistent Nonacene Derivative". Journal of the American Chemical Society. 132 (4): 1261–3. doi:10.1021/ja9095472. PMID 20055388.
  9. Purushothaman, Balaji; Bruzek, Matthew; Parkin, Sean; Miller, Anne-Frances; Anthony, John (2011). "Synthesis and Structural Characterization of Crystalline Nonacenes". Angew. Chem. Int. Ed. Engl. 50 (31): 7013–7017. doi:10.1002/anie.201102671. PMID 21717552.
  10. Nonacene Generated by On-Surface Dehydrogenation Rafal Zuzak, Ruth Dorel, Mariusz Krawiec, Bartosz Such, Marek Kolmer, Marek Szymonski, Antonio M. Echavarren, Szymon Godlewski, ACS Nano, 2017, 11 (9), pp 9321–9329 doi:10.1021/acsnano.7b04728
  11. Decacene: On-Surface Generation J. Krüger, F. García, F. Eisenhut, D. Skidin, J. M. Alonso, E. Guitián, D. Pérez, G. Cuniberti, F. Moresco, D. Peña, Angew. Chem. Int. Ed. 2017, 56, 11945. doi:10.1002/anie.201706156
  12. Eisenhut, Frank; Kühne, Tim; García, Fátima; Fernández, Saleta; Guitián, Enrique; Pérez, Dolores; Trinquier, Georges; Cuniberti, Gianaurelio; Joachim, Christian; Peña, Diego; Moresco, Francesca (2020-01-28). "Dodecacene Generated on Surface: Reopening of the Energy Gap". ACS Nano. 14 (1): 1011–1017. arXiv:2004.02517. doi:10.1021/acsnano.9b08456. ISSN 1936-0851. PMID 31829618. S2CID 209341741.
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