Acene


The acenes or polyacenes are a class of organic compounds and polycyclic aromatic hydrocarbons made up of linearly fused benzene rings. 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:
NameNumber of ringsMolecular formulaStructural formula
Anthracene3C14H10
Tetracene4C18H12
Pentacene5C22H14
Hexacene6C26H16
Heptacene7C30H18

Hexacene is not stable in air, and dimerises upon isolation. Heptacene is very reactive and has only been isolated in a matrix. However, bis 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 and nonacene 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 and decacene have been reported.

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.