Hexacene
Encyclopedia
Hexacene is an aromatic molecule consisting of six linearly-fused benzene rings. Hexacene and its derivatives are investigated for potential applications as organic semiconductor
.
Hexacene is one of a series of linear acene
s, the previous one being pentacene
(five fused benzene rings) and the next one being heptacene
(seven fused benzene rings).
Hexacene is very unstable, being highly reactive in the 6, 15 positions due to pi electron localization. Its spectra must be collected on freshly purified samples handled in an inert atmosphere such as nitrogen or argon. Only with very large substituents it is possible to isolate an hexacene for instance the compound 6,15-bis(tri-t-butylsilylethynyl)hexacene which melts with decomposition at 96°C.
The first reported synthesis of hexacene itself dates back to 1942 In 1955 the compound is synthesized by dehydrogenation
of hexacosadehydrohexacene by palladium on carbon
. In 1982 hexacene is reported as a bluish green compound with decomposition at 380 degrees. In 2007, a research group claimed the first reproducible unsubstituted hexacene synthesis (invalidating the previous claims) based on photochemical decarbonylation of a diketone
precursor :
The compound cannot be isolated: it dimerizes even at concentration as low as 10−4 M and reacts in solution with oxygen to the organic peroxide
. In a PMMA polymer matrix on the other hand these side-reactions are limited and the compound can survive up to 12 hours. The next homologue heptacene
also studied by this group, is even more unstable (decomposes within 4 hours).
Organic semiconductor
An organic semiconductor is an organic material with semiconductor properties. Single molecules, short chain and organic polymers can be semiconductive. Semiconducting small molecules include the polycyclic aromatic compounds pentacene, anthracene, and rubrene...
.
Hexacene is one of a series of linear acene
Acene
Acenes or polyacenes is 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...
s, the previous one being pentacene
Pentacene
Pentacene is a polycyclic aromatic hydrocarbon consisting of five linearly-fused benzene rings. This highly conjugated compound is an organic semiconductor. The compound generates excitons upon absorption of ultra-violet or visible light; this makes it very sensitive to oxidation...
(five fused benzene rings) and the next one being heptacene
Heptacene
Heptacene is an organic compound and a polycyclic aromatic hydrocarbon and the seventh member of the acene or polyacene family of linear fused benzene rings...
(seven fused benzene rings).
Hexacene is very unstable, being highly reactive in the 6, 15 positions due to pi electron localization. Its spectra must be collected on freshly purified samples handled in an inert atmosphere such as nitrogen or argon. Only with very large substituents it is possible to isolate an hexacene for instance the compound 6,15-bis(tri-t-butylsilylethynyl)hexacene which melts with decomposition at 96°C.
The first reported synthesis of hexacene itself dates back to 1942 In 1955 the compound is synthesized by dehydrogenation
Dehydrogenation
Dehydrogenation is a chemical reaction that involves the elimination of hydrogen . It is the reverse process of hydrogenation. Dehydrogenation reactions may be either large scale industrial processes or smaller scale laboratory procedures....
of hexacosadehydrohexacene by palladium on carbon
Palladium on carbon
Palladium on carbon, often referred to as Pd/C, is a form of palladium used for catalysis. It is usually used for catalytic hydrogenations in organic chemistry...
. In 1982 hexacene is reported as a bluish green compound with decomposition at 380 degrees. In 2007, a research group claimed the first reproducible unsubstituted hexacene synthesis (invalidating the previous claims) based on photochemical decarbonylation of a diketone
Diketone
A diketone is a molecule containing two ketone groups. The simpliest diketone is diacetyl, also known as 2,3-butanedione. Diacetyl, acetylacetone, and hexane-2,5-dione are examples of 1,2-, 1,3-, and 1,4-diketones, respectively...
precursor :
The compound cannot be isolated: it dimerizes even at concentration as low as 10−4 M and reacts in solution with oxygen to the organic peroxide
Organic peroxide
Organic peroxides are organic compounds containing the peroxide functional group . If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RCOOR. The O-O bond easily breaks and forms free radicals of the form RO·...
. In a PMMA polymer matrix on the other hand these side-reactions are limited and the compound can survive up to 12 hours. The next homologue heptacene
Heptacene
Heptacene is an organic compound and a polycyclic aromatic hydrocarbon and the seventh member of the acene or polyacene family of linear fused benzene rings...
also studied by this group, is even more unstable (decomposes within 4 hours).