organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...

, the acenes or polyacenes are a class of

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

s and

polycyclic aromatic hydrocarbon A Polycyclic aromatic hydrocarbon (PAH) is any member of a class of organic compounds that is composed of multiple fused aromatic rings. Most are produced by the incomplete combustion of organic matter— by engine exhaust fumes, tobacco, incine ...

s made up of

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

() rings which have been linearly fused. They follow the general

molecular formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as paren ...

. The larger representatives have potential interest in

optoelectronic Optoelectronics (or optronics) is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, ''light'' often includes invisible forms of radia ...

applications and are actively researched in chemistry and

electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...

. Pentacene has been incorporated into

organic field-effect transistor An organic field-effect transistor (OFET) is a field-effect transistor using an organic semiconductor in its channel. OFETs can be prepared either by vacuum evaporation of small molecules, by Polymer solution casting, solution-casting of polymer ...

s, reaching

charge carrier In solid state physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. ...

mobilities as high as 5 cm²/Vs. The first 5 unsubstituted members are listed in the following table: 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 Conjugation or conjugate may refer to: Linguistics *Grammatical conjugation, the modification of a verb from its basic form *Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics *Complex conjugation, the change o ...

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 Graphene () is a carbon allotrope consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice, honeycomb planar nanostructure. The name "graphene" is derived from "graphite" and the suffix -ene, indicating ...

. 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 In chemistry, a diradical is a chemical species, molecular species with two electrons occupying molecular orbitals (MOs) which are degenerate energy level, degenerate. The term "diradical" is mainly used to describe organic compounds, where most ...

but a closed-shell compound with the lowest HOMO-LUMO gap reported for any acene, an observation in violation of

Kasha's rule Kasha's rule is a principle in the photochemistry of electronically excited molecules. The rule states that photon emission (fluorescence or phosphorescence) occurs in appreciable yield only from the lowest excited state of a given multiplicity. ...

. 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) 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.

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

helicene In organic chemistry, helicenes are aromatic ortho substituent, ortho-condensed Polycyclic compound, polycyclic Aromaticity, aromatic compounds in which Benzene, benzene rings or other aromatics are angularly annulation, annulated to give helix, ...

s have a helical structure. File:Heptacene 200.svg, Heptacene File:7-phenacene.svg, henacene File:M-heptahelicene.svg, ''M''-heptahelicene Benz nthracene, an isomer of tetracene, has three rings connected in a line and one ring connected at an angle.

References

{{Authority control Conductive polymers Organic semiconductors