Synthesis, Structure, and Photochemistry of 5,14‐Diketopentacene

Abstract

Abstract5,14‐α‐Diketopentacene, a structural isomer of 6,13‐α‐diketopentacene, was prepared from pentacene in three steps. In addition to the typical n–π* absorption of the diketone moiety at around 468 nm and the anthracene‐like absorption at 333, 349, and 367 nm, a broad absorption was observed at around 386 nm, which could be assigned to an intramolecular charge‐transfer absorption from anthracene to the diketone moiety. 5,14‐α‐Diketopentacene could be converted into pentacene quantitatively by photoirradiation at 405 and 468 nm in toluene with quantum yields of 2.3 and 2.4 %, respectively, and these values are higher than the quantum yield of 1.4 % obtained for 6,13‐α‐diketopentacene irradiated at 468 nm. The quantum yields in acetonitrile were lowered to 0.33 and 0.28 % with irradiation at 405 and 468 nm. The crystal structure of 5,14‐α‐diketopentacene showed a CH–π interaction and π–π stacking between neighbouring anthracene and benzene moieties. The lower solubility of 5,14‐α‐diketopentacene compared with the 6,13‐isomer could be explained by this crystal structure.