Synthesis and Properties of New N-Heteroheptacenes for Solution-Based Organic Field Effect Transistors

A series of N-heteroheptacenes was synthesized from ortho-thiophene-substituted aryl azides using a Rh₂^II-catalyzed C−H bond amination reaction to construct the thienoindole moieties. This reaction tolerated the presence of electron-donating or withdrawing groups on the aryl azide without adversely affecting the yield of the amination reaction. The central thiophene ring was created from two thienoindole pieces through a Pd-catalyzed Stille reaction to install the thioether followed by a Cu-mediated Ullman reaction to trigger the cyclization. The photophysical and electrochemical properties of the resulting focused library of N-heteroheptacenes revealed that the electronic nature is controlled by the arene substituent while single crystals grown reveal that the packing motif is influenced by the N-substituent. Solution-processed thin-film OFET devices were fabricated with the N-heteroheptacenes, and one exhibited a hole-mobility of 0.02 cm² V⁻¹ s⁻¹.