Ab is(benzobuta)tetraazapentacene derivative was reduced to its radicala nion and its dianion, using potassium [18]crown-6 anthracenide in THF.B othr educed species were characterizedb yU V/Vis spectroscopy of the isolated species and by spectroelectrochemistry.T wo distinct single-crystals tructures of the dianion and an EPR spectrum of the radical anion were obtained. Contraryt o other azaacenes, the lowest energy absorption in the UV/ Vis spectrum of the dianion is redshifted in comparison to that of the neutral compound.During the past decade, the chemistry of large azaacenesa nd azaarenes has experienced as trongr evival. While azapentacenes have been known since 1967, [1] azatetracenesw ere described as early as 1901. [2] However, azaarenes and azaacenes have only attracted increased attention since we developed a number of robust protocols to prepare privileged aromatic ortho-diamines;t hese allow the synthesis of azaacenes up to azaheptacenes. [3] Other groups (Mastalerz, [4] Zhang, [5] Mateo-Alonso, [6] Koert [7] etc.) also contributed to this area, providing novel structures and properties. The breakthrough was Miao's discoveryt hat the symmetrical tetraazapentacene (TAP) displays high n-channel chargem obilities. [8, 9] Upon halogenation of TAP, the mobilities increasee ven further, reaching up to 27 cm 2 V À1 s À1 . [10] While the size of stable azaacenes is limited, interspersed cyclobutadiene units increaset he number of Clar sextets and should allow the synthesis of larger targets. [11] Cyclobutadiene-fused acenes showh igh p-channel mobilities in organic thin-film transistors. [12] The charge carriers in TAP-based transistors must be the small concentration of radicala nions generatedu pon charge injection. We have prepared these carriers, that is, the radical anionso fanumber of azapentacenes, as discrete species in solution and in the solid state, and investigated their structural and spectroscopicp roperties. [13] In this Communication we describe the formation andp roperties of the radical anion and the dianion of ad oubly benzobuta-annelated tetraazapentacene, 1,w hich also features TAPa sas tructural element (Scheme 1, blue structure).Compound 1 [14] was treated with {[18]crown-6}K anthracenide in THF to give consecutively the radical anion and the dianion (reduction potentials of À1.12 and À1.52 V; cyclic voltammetry vs. ferrocene). The radical anion of 1 is less stable than the TAP radical anion in air,a st he electron affinity of 1 is lower by about 0.6 eV.C alculations (Table 1) of the relative energies of the neutral,a nion and dianion of 1 reveal the anion to be more stable than the neutralf orm by 3.64 eV in THF,a nd the dianion to be more stable than the anion by another 2.8 eV at the DFT/CAM-B3LYP/6-311 ++G** level supporting the lack of disproportionation.The aromatic region of the 1 HNMR spectra of 1 and its dianion are showni nF igure 1. Reduction leads to as ignificant Scheme1.Reduction of abis(benzobuta)tetraazapentacene derivative 1 and depiction of the TAP-substruct...
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