Synthesis, Structure, and Properties of Peripheral BN-Fused Fluoranthenes

A versatile synthetic strategy has been developed for the construction of a series of peripherally BN‑embedded fluoranthenes. The key step involves a tandem deprotonation/cyclization sequence from readily accessible imine precursors, affording the desired BN‑fluoranthene cores in good yields. Site‑selective bromination at the C‑5 position, which is remote from the BN‑embedded ring, was achieved and exploited for subsequent Suzuki and Sonogashira cross‑coupling reactions to install various aryl and alkynyl substituents. Structural analyses, including X‑ray crystallography and theoretical calculations, confirm a highly planar architecture with delocalized frontier molecular orbitals and show that replacing a C═C unit with a B-N bond markedly alters the local aromaticity of the five‑membered ring. When examined for their optical behavior, most of the synthesized derivatives exhibited intense fluorescence in dichloromethane, with quantum yields as high as 84%. Notably, while alkyl and aryl substituents caused little change in the spectral profiles, the incorporation of conjugated alkynyl groups led to consistent bathochromic shifts in both absorption and emission.