Synthesis, Photophysical, and Redox Properties of Naphtho[2,1-b]-Fused AzaBODIPYs with Ultradeep Lowest Unoccupied Molecular Orbital Levels

A streamlined chromatography-free synthesis of conformationally restricted six-membered-ring-fused azaBODIPYs via a classical Michael addition-cyclization sequence has been developed. Subsequent stepwise 2,3-dichloro-5,6-dicyano-1,4-benzoquinone-mediated dehydrogenative aromatization yields the first naphtho[2,1-b]-fused azaBODIPYs, demonstrating progressively lowered lowest unoccupied molecular orbital (LUMO) levels (up to -4.39 eV) upon oxidation, which aligns with enhanced electron-accepting behavior. These novel fused azaBODIPYs show intense near-infrared absorption and form radical anions in the presence of cobaltocene, exhibiting a red-shifted absorption maxima at 877 nm.