2,6-Diaryl-9,10-anthraquinones as models for electron-accepting polymers

Abstract

Anthraquinone derivatives have been little used in microelectronics though they are attractive scaffolds due to their electron-accepting properties. As part of a preliminary study, a series of conjugated anthraquinone derivatives has been synthesised. The crystal structures of 2,6-diphenyl-9,10-anthraquinone, 2,6-di(thien-2′-yl)-9,10-anthraquinone and 2,6-bis(9′,9′-dioctylfluoren-2′-yl)-9,10-anthraquinone are presented. The UV-Vis absorption spectra of the anthraquinone derivatives synthesised are characterised in each case by the presence of a very intense long-wavelength band that we attribute to intramolecular charge transfer (CT) from the electron-rich aromatic substituents to the electron-deficient anthraquinone moiety. The fluorescence of these compounds is also strongly affected by this intramolecular CT and quantum yields up to 6.8 × 10⁻² were found in solution. This long wavelength emission in the yellow-orange region is reminiscent of the fluorescence of fluorenone derivatives substituted with aromatic groups, including fluorenone-containing polyfluorenes. The relatively high electron affinity of these compounds together with their tunable emission suggests their potential application in organic electronics. Additionally, the electrochemical behaviour of the present compounds reveals a partial destabilisation of both of the aromatic rings in the anthraquinone moiety. Finally, chemical doping experiments were conducted. These clearly show the extended conjugation characteristic of the reduced states of anthraquinone.