Quadruply B←N-Fused Dibenzo-azaacene with High Electron Affinity and High Electron Mobility.

For many years, organoboron compounds have been expected to show excellent electron injecting and transporting properties. However, LUMO energy levels (ELUMO) of B-containing π-conjugated molecules are mostly higher than -4.0 eV and their electron mobilities are usually less than 10-2 cm2 V-1 s-1. In this work, we experimentally prove the remarkably high electron affinity and high electron mobility of organoboron compounds. Our strategy is to incorporate multiple boron-nitrogen coordination bonds (B←N) into azaacenes. We synthesized quadruply B←N-fused dibenzo-azaacene (QBNA) through one-pot multifold borylation cyclization reaction. The incorporation of four B←N units greatly changes the electronic structures and properties and significantly downshifts the electronic energy levels of QBNA. QBNA shows a ELUMO of as low as -4.58 eV, which is among the lowest for n-type organic semiconductors. Single-crystal organic field-effect transistors (SC-OFETs) of QBNA display unipolar n-type characteristic with an electron mobility of up to 1.60 cm2 V-1 s-1 together with excellent ambient stability. This study thus provides a design strategy for high-performance n-type organic semiconductors and high electron-affinity π-systems based on organoboron chemistry.