Synthesis, Structures, and Photophysical Properties of Zigzag BNBNB-Embedded Anthracene-Fused Fluoranthene

Three zigzag BNBNB-embedded anthracene-fused fluoranthenes are synthesized from 1,3,2-benzodiazaboroles through an indole-type N-directed C–H borylation reaction. Single-crystal X-ray diffraction analyses confirm the double bond character of all four alternating B–N bonds and reveal the five-center four-π-electron nature of the BNBNB group. Experimental spectra and density functional theory calculations indicate that borylation remarkably enhances the planarity, extends π-conjugation, and leads to a bathochromic shift in the absorption and emission bands, with remarkable fluorescence quantum yields in solution (92%).