Azaacenes are well-described in literature as π-conjugated systems with applications from emitters in organic light-emitting diodes (OLEDs), to electron-transporters in solar cells (SC) and n-type semiconductors in organic field-effect transistors (OFETs). 6,13-Bis(triisopropylsilylethynyl)-5,7,12,14-tetraazapentacene (TIPSTAP) is a classic example of this class of electron transport materials. Peripherial substitution of the aromatic system with four bromine atoms, through a high yielding Hinsberg cyclocondensation route, leads to higher electron affinity in the compound and shows increased electron mobility in OFETs. To investigate the charge transport in OFETs, the tetrabrominated TIPSTAP (Br4-TIPSTAP) is reduced to the radical anion and dianion. While the dianion oxidizes to the radical anion within a few minutes when exposed to air, the monoanion is stable in solution for several weeks. Crystal analysis and electron paramagnetic resonance indicate that the unpaired electron is more located in the outer rings in Br4-TIPSTAP stabilized by the negative inductive effect of the bromide. Furthermore the tetrahalogenation of TIPSTAP opens the possibility to design a new class of symmetrical substituted azaacenes with different electronic properties and morphologies by using Suzuki and Negishi cross-coupling reactions.

Tetrabromo-TIPS-tetraazapentacene and its airstable radical anion

256th National Meeting (2018)

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