s-Dipentacene:  Structure, Spectroscopy, and Temperature- and Pressure-Dependent Photochemistry

Abstract

We report the synthesis, characterization, spectroscopy, and photochemistry of s-dipentacene (see Figure ). The symmetric addition product dimer of pentacene (s-dipentacene) is formed upon irradiation of a solution of pentacene. The structure of s-dipentacene was determined by X-ray crystallography. The crystals had a space group symmetry of P1̄ with two molecules per unit cell. One molecule in the unit cell was accompanied by two dichloromethane molecules of solvation. Photodecomposition of s-dipentacene, dispersed in a poly(methyl methacrylate) (PMMA) host matrix, to pentacene was studied. Spectroscopic evidence shows that this photodecomposition proceeds through a trapped intermediate both at low temperature (∼12 K) and at room temperature under high pressure (13 kbar). This intermediate is assigned as a “broken dimer” of two pentacene molecules trapped in the PMMA host. We previously reported similar results in the photolysis of both dianthracene and ditetracene at low temperatures, but this is the first report of broken dimer formation at room temperature under high pressure.

Degradation Mechanisms and Reactions in Organic Light-Emitting Devices

“…456 One should mention that this observation may contribute to a cyclization reaction after Coppo and Yeates. 457 As expected, other pentacene derivatives are known to undergo the 4 + 4 cycloaddition 457,458 or will oxidize in the presence of oxygen or even will be excited for further reactions. 459 Such photo oxidation effects are well-known for condensed materials like rubrene and naphthacene as well.…”

Beyond Pentacenes: Synthesis and Properties of Higher Acenes

“…The centrosymmetric dimer 24 formed by reaction between the two most reactive sites (C7 and C14) and in this sense resembles the photodimers of parent anthracene, tetracene, and pentacene [38]. The dimer 25 formed in the dark reaction resulted from reaction of the most reactive ring of one monomer with the next to terminal ring of the other molecule [33].…”

“…Note that the colorless pentacene photodimer 38 (from a [4+4] cycloaddition, Fig. 17) is reported to be easily oxidized under ambient conditions, although it only consists of naphthalene subunits [38]. Hence, facile oxidation of heptacene dimers is also likely.…”

Höhere Acene: vielseitige organische Halbleiter

“…26 ist durch Bestrahlung von Pentacen in sauerstofffreiem 1-Chlornaphthalin mit l > 440 nm bei 120 8C präparativ zugänglich; das Produkt fällt dabei im Verlauf mehrerer Tage als weißer Feststoff aus. [116] Bei der Bestrahlung entsteht in stark untergeordneter Menge auch das asymmetrische Dimer (27). Eine Kristallstrukturanalyse von 26 lieferte für die Länge der Bindungen zwischen den beiden Pentaceneinheiten einen hohen Wert von 1.58 .…”