Backbone Engineering of Carbon-Centered NHC-Derived Diradicals: From Electronic State Tuning to High-Performance Organic Field-Effect Transistors.

Abstract

Diradicals have gained interest for their unique electronic properties and potential applications in organic electronics and semiconductors. However, precise manipulation of electronic states and achieving satisfactory device performance remain challenging. Herein, we report the synthesis and characterization of tetraphenylethylene-bridged salts and their neutral diradical counterparts obtained via two-electron reduction. With extended conjugation and electron-withdrawing N-heterocyclic carbene (NHC) backbones, enhanced open-shell character is observed. Through this systematic study, a backbone engineering strategy is established that allows precise control over spin states and diradical character in carbon-centered NHC diradicals. Leveraging this strategy, compound 2d, with moderate diradical character induced by extended conjugated structures and strong electron-withdrawing groups, was employed in a spin-coated organic field-effect transistor (OFET) device. The device achieved a record-high hole mobility of 4.53 cm²·V^-1·s^-1, representing exceptional performance among open-shell organic semiconductors for high-performance OFETs. This not only demonstrates the outstanding charge-transport capability of 2d but also underscores the significant potential of this approach for developing functional open-shell organic semiconductors.