ImageFile = Pentacene.png
IUPACName = Pentacene
Section1 = Chembox Identifiers
CASNo = 135-48-8
PubChem = 24886995
SMILES = c45cc3cc2cc1ccc
Section2 = Chembox Properties
Formula = C22H14
MolarMass = 278.36 g/mol
Appearance = Dark powder
MeltingPt = > 300 °C; sublimes at 372-374 °C
Section3 = Chembox Hazards
Autoignition = ; making it sensitive to oxidation. For this reason, its originally purple color in the solid state (a powder) slowly turns green upon prolonged exposure to air and light.
Pentacene is a promising candidate for the use in organic
thin film transistors and OFETs. It is one of themost thoroughly investigated conjugated organic molecules with a high application potential due to a hole mobility in OFETs of up to 5.5 cm2V-1s-1 (almost comparable to amorphous silicon). ["Organic Electronic Devices and Their Functional Interfaces, N. Koch, ChemPhysChem, 2007, 8(10) pp 1438-1455," [http://www3.interscience.wiley.com/cgi-bin/abstract/114275266/ABSTRACT Link] ]
buckminsterfullerenePentacene is used in the development of organic photovoltaic devices. ["Nanoimprinted large area heterojunction pentacene-C60 photovoltaic device, D. M. Nanditha, M. Dissanayake, A. A. D. T. Adikaari, Richard J. Curry, Ross A. Hatton, and S. R. P. Silva, Applied Physics Letters, 2007 90 pp 253502. [http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APPLAB000090000025253502000001&idtype=cvips&gifs=yes] ] " ["Efficiently Organic: Researchers Use Pentacene To Develop Next-generation Solar Power" sciencedaily.com [http://www.sciencedaily.com/releases/2004/12/041220005834.htm Link] ]
Pentacene is one of a series of linear
acenes, the previous one being tetracene( four fused benzene rings) and the next one being hexacene(six fused benzene rings).
Pentacenes can be prepared in the laboratory by extrusion of a small volatile component. In one such experimental procedure
carbon monoxideis liberated from a precursor at 150°C."A new type of soluble pentacene precursor for organic thin-film transistors" Kew-Yu Chen, Hsing-Hung Hsieh, Chung-Chih Wu, Jiunn-Jye Hwang and Tahsin J. Chow Chem. Commun., 2007, 1065 - 1067, DOI| 10.1039/b616511g] The precursor is reported to have some solubility in chloroformand is therefore amiable to spin coating. Pentacene is reported to be soluble in hot chlorinated benzenes, such as 1,2,4-trichlorobenzene, from which it can be recrystallized to form platelets
Although Pentacene looks just like any aromatic compound such as
anthraceneits aromatic properties are ill defined and for this reason the compound and its derivatives are topic of research. A tautomeric chemical equilibriumexists between "6-methylene-6,13-dihydropentacene" and 6-methylpentacene.
This equilibrium is entirely in favor of the methylene compound. Only by heating to a solution of the compound to 200°C does a small amount of the pentacane develop as evidenced by the emergence of a red-violet color. According to one study ["Why 6-Methylpentacene Deconjugates but Avoids the Thermally Allowed Unimolecular Mechanism" Joseph E. Norton, Brian H. Northrop, Colin Nuckolls, and K. N. Houk
Org. Lett.; 2006; 8(21) pp 4915 - 4918; (Letter) DOI|10.1021/ol062012g] the reaction mechanismfor this equilibrium is not based on an intramolecular 1,5-hydride shiftbut on a bimolecular free radicalhydrogen migration. In contrast, isotoluenes with the same central chemical motif easily aromatize.
Pentacene reacts with elemental
sulfurin 1,2,4-trichlorobenzene to the compound hexathiapentacene. ["Hexathiapentacene: Structure, Molecular Packing, and Thin-Film Transistors" Alejandro L. Briseno, Qian Miao, Mang-Mang Ling, Colin Reese, Hong Meng, Zhenan Bao, and Fred Wudl J. Am. Chem. Soc.; 2006; 128(49) pp 15576 - 15577; (Communication) DOI|10.1021/ja066088j.] X-ray crystallographyshows that all the carbon-to-sulfur bond lengths are roughly equal (170 picometer) and from there it follows that resonance structures B and C with complete charge separation are more significant than structure A.
: In the crystal phase the molecules display
aromatic stacking interactions whereby the distance between some sulfur atoms on neighboring molecules can become less (337 pm) than the sum of two Van der Waals radii (180 pm)
Like the related
tetrathiafulvalene, this compound is studied in the field of organic semiconductors.
The acenes may appear as planar and rigid molecules, but in fact they can be very distorted. The pentacene depicted below: ["Synthesis, Structure, and Resolution of Exceptionally Twisted Pentacenes" Jun Lu, Douglas M. Ho, Nancy J. Vogelaar, Christina M. Kraml, Stefan Bernhard, Neal Byrne, Laura R. Kim, and Robert A. Pascal, Jr.
J. Am. Chem. Soc.; 2006; 128(51) pp 17043 - 17050; (Article) DOI|10.1021/ja065935f]
has an end-to end twist of 144° and is sterically stabilized by the six
phenylgroups. The compound can be resolved into its two enantiomers with an unusually high reported optical rotationof 7400° although racemizationtakes place with a chemical half-lifeof 9 hours.
Pentacenes are examined as potential
dichroic dyes. The pentacenoquinone displayed below is fluorescentand when mixed with liquid crystal E7 mixturea dichroic ratioof 8 is reached. [Synthesis and Characterization of Fluorescent Acenequinones as Dyes for Guest-Host Liquid Crystal DisplaysZhihua Chen and Timothy M. Swager Org. Lett.; 2007; 9(6) pp 997 - 1000; (Letter) DOI|10.1021/ol062999m] [in the synthesis of this compound, the starting material is reacted with 1,4-naphthoquinoneand DPT. DTP converts the oxo-norbornadiene to an intermediary furan. The second step is oxidation by PPTS] The longer the acene the better it is able to align itself in a nematic liquid crystalphase.
* [http://www.chm.bris.ac.uk/motm/pentacene/pentacene.htm facts about pentacene] , retrieved Apr. 17, 2006
* [http://www.nature.com/news/2007/070423/full/070423-11.html] , retrieved May 2, 2007
* [http://technology.newscientist.com/channel/tech/mg19626325.400-organic-transistor-improves-with-age.html?feedId=online-news_rss20 Organic transistor improves with age] , New Scientist, "2 December 2007"
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