Three Birds with One Stone: Synthesis and Properties of 4,5-π-Extended Fluorenones

Fluorenones are pivotal cores in medicinal chemistry and materials science; however, π-extension at the sterically hindered 4,5-positions remains a significant synthetic challenge. This work establishes an efficient and divergent strategy for constructing three distinct classes of 4,5-π-extended fluorenone derivatives using 4,5-diyne-9-fluorenone (1,7-diyne) as the key precursor. The molecular structures of the representative compounds were unambiguously confirmed by X-ray crystallography, revealing twisted conformations. Photophysical studies and DFT calculations revealed that the π-extension significantly narrowed the HOMO-LUMO gap compared to phenanthrenone. The optoelectronic properties of these materials are highly dependent on the core architecture and substituent positioning. This approach overcomes the traditional synthetic limitations of 4,5-functionalized fluorenones, providing direct access to a library of complex polycyclic aromatic hydrocarbons with tailored properties for potential applications as novel functional materials.