Pushing the Length Limit of Dihydrodiboraacenes: Synthesis and Characterizations of Boron‐Embedded Heptacene and Nonacene

Abstract Boron‐embedded heteroacenes (boraacenes) have attracted enormous interest in organic chemistry and materials science. However, extending the skeleton of boraacenes to higher acenes ( N ≥6) is synthetically challenging because of their limited stability under ambient conditions. Herein, we report the synthesis of boron‐embedded heptacene ( DBH ) and nonacene ( DBN ) as the hitherto longest boraacenes. The former is highly stable (even after 240 h in tetrahydrofuran), while the latter is air‐sensitive with the half‐life ( t 1/2 ) of 11.8 min. The structures of both compounds are verified by single‐crystal X‐ray diffraction, revealing a linear backbone with an antiaromatic C 4 B 2 core. Photophysical characterizations associated with theoretical calculations indicate that both compounds exhibit highly efficient anti‐Kasha emissions. Remarkably, the air‐stable DBH manifests an ultrahigh photoluminescence quantum yield (PLQY) of 98±2 % and can be chemically reduced to its radical anion and dianion states, implying the value of boron‐doped higher acenes as novel functional materials.