Tandem Acylation/C–H Functionalization Cyclization to Access Indanone-Fused BODIPYs and Their NIR-Emissive α,α-Dimers with Deep LUMO Levels

Abstract Mono- and bis-indanone-fused BODIPYs are synthesized via tandem acylation and intramolecular C–H functionalization cyclization. This rigid fused-ring framework extends the π-conjugated system, affording red-shifted, intense absorption/emission and high quantum yields (>0.90). Regioselective FeCl3-mediated oxidative coupling yields the α,α-linked dimer, inducing a 216 nm redshift with emission maxima at 823 nm. Notably, the electron-withdrawing indanone units lower the LUMO to −4.10 eV and enable radical anions, an electronic property generally absent in conventional fused BODIPYs. Owing to their tunable absorption, bright emission, and good biocompatibility, these indanone-fused dyes enable high-contrast, multicolor lipid droplet (LD) imaging in living cells.