Acenaphthylene-Fused Angular and Linear π-Extension of Acridone

The direct functionalization of small heterocyclic molecules is an efficient strategy for constructing large heteroatom-doped polycyclic aromatic systems. However, due to the unique reactivity of acridone, π-extension on the benzene ring generally leads to the formation of angular-shaped acridone derivatives. In this study, we present the selective synthesis of both linear and angular π-extended acridone derivatives incorporating acenaphthylene units with intervening five-membered rings. This synthetic approach was successfully realized through a sequential process involving the Suzuki-Miyaura cross-coupling reaction followed by a palladium-catalyzed intramolecular arylation. The molecular structures of these acridone derivatives were unequivocally confirmed by crystallographic analysis. Comprehensive photophysical characterization, including UV/vis absorption and fluorescence spectroscopy, revealed distinct optical properties in both the solution and solid states, which were found to be highly dependent on the molecular structure. Furthermore, theoretical calculations were conducted to investigate the frontier molecular orbitals and assess molecular aromaticity, providing deeper insights into the electronic structures of these novel compounds.