Abstract
Pentacene is an organic semiconductor used in a variety of thin-film organic electronic devices. Although at least six separate syntheses of pentacene are known (two from dihydropentacenes, two from 6,13-pentacenedione and two from 6,13-dihydro-6,13-dihydroxypentacene), none is ideal and several utilize elevated temperatures that may facilitate the oxidation of pentacene as it is produced. Here, we present a fast (~2 min of reaction time), simple, high-yielding (≥90%), low temperature synthesis of pentacene from readily available 6,13-dihydro-6,13-dihydroxypentacene. Further, we discuss the mechanism of this highly efficient reaction. With this improved synthesis, researchers gain rapid, affordable access to high purity pentacene in excellent yield and without the need for a time consuming sublimation.
Highlights
Pentacene is a benchmark organic semiconductor in thin-film organic electronic devices due to its π-conjugated electronic structure, its relatively low HOMO-LUMO gap and the relatively high charge carrier mobility of its solid state films
Pentacene cannot be isolated from petroleum; it needs to be synthesized
The first synthesis of pentacene was accomplished by Clar in 1929 via a transfer dehydrogenation of 6,13-dihydropentacene using phenanthraquinone [10,11]
Summary
Pentacene is a benchmark organic semiconductor in thin-film organic electronic devices due to its π-conjugated electronic structure, its relatively low HOMO-LUMO gap and the relatively high charge carrier mobility of its solid state films. Hart reacted benzocyclobutene, an o-quinodimethane precursor, with anthracene-1,4-endoxide (prepared in a multi-step synthesis involving 2,3-dihydronaphthalene and furan) to produce a dihydropentacene hydrate that was dehydrated using HCl. A subsequent Pd/C catalyzed dehydrogenation produced pentacene (59% overall yield from anthracene-1,4-endoxide, Scheme 2). A fourth procedure to prepare pentacene involves the reaction of pentacene-6,13-dione in dry, boiling THF with LiAlH4 for 30 min followed by the addition of 6 M HCl and three additional hours of boiling. A fifth procedure to produce pentacene involves the reduction of 6,13-dihydro-6,13dihydroxypentacene using potassium iodide and sodium hyposulfite in boiling acetic acid for three hours (Scheme 5). In this way, pentacene is produced in 67% yield [18]. The improved synthesis utilizes HCl as co-reagent, involves shorter reaction times, does not require a sublimation step, and results in a significantly higher overall yield
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