Fused Pyrazine- and Carbazole-Containing Azaacenes: Synthesis and Properties

A new family of azaacenes has been designed and synthesized by incorporating the electron-withdrawing sp²-hybridized nitrogen of pyrazine and electron-donating nitrogen of carbazole in a molecular skeleton. Two different conjugated lengths of 8-ring aza-nonacene and 10-ring aza-undecene have been achieved by an efficient condensation reaction. The unique optoelectronic properties of these molecules were investigated using both experimental and theoretical techniques. The azaacenes show visible-region absorption and near-infrared (NIR) fluorescence. These compounds can serve as hole-transport semiconductors for solution-processed organic field-effect transistors (OFETs). Single-crystal transistor devices of one of the aza-nonacenes exhibit hole charge transport behavior with a hole mobility of 0.07 cm²/Vs and an on/off current ratio of 1.3x10⁶.