Dicyanocarbene-Induced Metal-Free Efficient Quinoidization for the Development of Fused N-Type Organic Semiconductors.

Dicyanomethylene-terminated quinoidal materials are promising n-type organic semiconductors featuring excellent electron mobilities and air stability. Traditional synthetic methods of these materials such as Takahashi reaction, require the use of expensive palladium catalyst and halogenated substrates. However, for electron-rich fused aromatic compounds, the poor stability after halogenation renders their halogenated derivatives unsuitable as reaction precursors. To address this issue, we present a new metal-free synthetic approach using 2-(dimethylsulfaneylidene)malononitrile as the quinoidization reagent, which is successfully applied to various electron-rich fused aromatic compounds, leading to the corresponding quinoidal compounds with high yields up to 94%. We proposed the reaction mechanism, and investigated the physical properties of four fused quinoidal materials based on highly electron-rich fused aromatic compounds, which are scarce to be synthesized by the traditional method. Furthermore, these fused quinoidal materials were utilized in field-effect transistors, achieving high electron mobilities up to 1.33 cm2 V-1 s-1. We provide an effective synthetic approach to expand the library of high-performance n-type small-molecule semiconductors.