BN-Isosteres of Nonacene with Antiaromatic B2C4 and N2C4 Heterocycles: Synthesis and Strong Luminescence

Embedding both boron and nitrogen into the backbone of acenes to generate their isoelectronic structures has significantly enriched the acene chemistry to offer appealing properties. However, only small BN-heteroacenes have been extensively investigated, with BN-embedded heptacenes as the hitherto longest BN-acenes. Herein, we report the synthesis of three new nonacene BN-isosteres via incorporating antiaromatic 1,4-dihydro-1,4-diborinine (B2C4) and 1,4-dihydropyrazine (N2C4) heterocycles. These BN-nonacenes represent a new length record in the field of BN-heteroacenes. The position of the boron- and nitrogen-embedded antiaromatic rings manifests substantial influence on the molecular orbital arrangement, and consequently, the radiative transition rate of BN-3 is greatly enhanced compared with BN-1 and BN-2, realizing a high fluorescence quantum yield of 92%. This work provides a novel design concept of BN-heteroacenes and reveals the importance of precisely BN-doping.