Mono‐ and Dianion of a Bis(benzobuta)tetraazapentacene Derivative

Abstract

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...

Crystalline Diradical Dianions of Pyrene‐Fused Azaacenes

“…In the case of [(18‐c‐6)K(THF) 2 ] + [(18‐c‐6)K] + ⋅ 1 2−.. , the K1 ion is fully separated from the pyrene‐fused azaacene, whereas there is a weak interaction between the K2 cation and dianion part with K2−C11 and K2−C12 distances of 3.636 and 3.671 Å, respectively (Figure a). Notably, both potassium cations do not interact with the nitrogen atoms at all; this finding is similar to the cases of II 2− and III 2− . By contrast, two K + ions in [(18‐c‐6)K(THF)] 2 2+ ⋅ 2 2−.. are equivalent, both of which are coordinated by one 18‐c‐6, two THF molecules, and one N1−C9 bond of the pyrene‐fused azaacene moiety with the K1−N1 and K1−C9 distances of 2.929(4) Å and 3.387 Å, respectively (Figure b).…”

“…Since the discovery of high n‐channel charge mobility of a silylethynylated tetraazapentacene by the group of Miao, the anionic azaacene species are of increasing interest. In particular, the groups of Marder, Bunz, and Dreuw have successfully isolated and structurally characterized a series of radical anions and dianions of azaacenes . Despite rapid progress in this area, radical species of the negatively charged azaacenes are exclusively limited to monoradical anions, and the extant examples of azaacene dianions ( I 2− – IV 2− , Scheme a–c) are closed‐shell singlets.…”

The Radical Anion and Dianion of Benzo[3,4]cyclobuta[1,2-b]phenazine

“…Unfortunately, we could not obtain single crystals of the dianion of A1 , while in the case of P2 we obtained single crystals of both the radical anion and the dianion (Figures , ). As seen with other charged azaacenes, the potassium ions are separated from the large acene backbones. However, in the case of P2 2– (polymorph A), in which the K + ion lacks the two THF molecules usually coordinated to it on either side of the 18-crown-6 moiety, there appears to be an electrostatic interaction between the potassium ion and the π-system.…”

Crystalline Diradical Dianions of Pyrene‐Fused Azaacenes

“…The UV/Vis absorption spectra of 1C À and 2C À in THF display two fairly weak and broad absorption bands at 903 nm and 695 nm for 1C À and 909 nm and 702 nm for 2C À (Figures 2 d and S4), respectively, which can be attributed to the HOMO(a)! LUMO + 2(a) transitions at the (TDDFT)//UWB97XD/ 6 CC, the K1 ion is fully separated from the pyrene-fused azaacene, whereas there is a weak interaction between the K2 cation and dianion part with K2 À C11 and K2 À C12 distances of 3.636 and 3.671 , respectively (Figure 3 a). Notably, both potassium cations do not interact with the nitrogen atoms at all; this finding is similar to the cases of II 2À [4] and III 2À .…”

“…Notably, both potassium cations do not interact with the nitrogen atoms at all; this finding is similar to the cases of II 2À [4] and III 2À . [6] By contrast, two K + ions in [(18-c-6)K(THF)] 2…”