Synthesis and photophysical properties of conformationally restricted difluoroboron β-diketonate complexes of 1-indanone derivatives

A series of conformationally restricted difluoroboron β-diketonate complexes (BF₂bdks) was easily synthesized from (Z)-2-(1-arylhydroxyliden)-1-indanone derivatives in good to excellent yields. These dyes displayed the lowest energy absorption maxima in the range of 370–408 nm and possess molar absorption coefficients (ε) ranging from 8000 to 47 000 M⁻¹cm⁻¹ in CH₂Cl₂. All the absorption spectra of the BF₂bdks systems were red shifted (5–43 nm) as compared to the parent difluoroboron 1,3-diphenyl-β-diketonate complex (BF₂dbm). Their emission maxima were centered on 406–432 nm and the fluorescence quantum yields (Φ) were in the range of 0.33–0.87, which are in all cases much higher than the found for BF₂dbm. These observations demonstrate the effectiveness of improving the dye quantum yield by restricting the intramolecular C–C bond rotation.