Diboron‐Embedded Heteroacenes With Systematically Varied Central π‐Skeletons and Fusion Modes

Diboron‐embedded heteroacenes with systematically varied central π‐skeletons and fusion modes were synthesized via one‐pot cyclative borylation using benzene, thieno[3,2‐ b ]thiophene, or dithieno[3,2‐ b :2′,3′‐ d ]thiophene cores, affording six derivatives with C 2h or C 2v symmetry. Their photophysical and electrochemical properties, including absorption and emission wavelengths and sequential reduction behavior during cyclic voltammetry, depend primarily on fusion mode rather than π‐core size. Single‐crystal analysis, in turn, revealed that molecular symmetry governs packing modes, where C 2h derivatives exhibited limited π‐overlap due to shielding by mesityl groups on both π‐faces, while C 2v derivatives formed efficient π–π stacking with large intermolecular overlap despite the presence of the bulky mesityl groups. Notably, one of the derivatives adopted a uniform columnar structure via continuous π–π stacking, establishing a design principle for solid‐state organization in boron‐embedded heteroacenes.