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Class of chemical compounds From Wikipedia, the free encyclopedia
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.
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]
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. 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. [13]
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.
Benz[a]anthracene, an isomer of tetracene, has three rings connected in a line and one ring connected at an angle.
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