Synthesis and spectroscopic properties of some new difluoroboron bis-β-diketonate derivatives.

Six new bis-β-diketones (RCOCH2CO-C7H7N-COCH2COR) were synthesized from 3,5-diacetyl-2,6-dimethylpyridine via Claisen condensation with the corresponding esters, and then reacted with boron trifluoride etherate to afford difluoroboron bis-β-diketonate derivatives. Their spectroscopic properties were investigated by UV-vis, FTIR, (1)H NMR and fluorescence spectroscopic techniques. It was found that these boron complexes exhibited violet or blue fluorescence emission at 422-445nm and possessed high extinction coefficients. The results indicate that the extending π-conjugation can increase the fluorescence intensity and quantum yield for these boron complexes. Especially, the compound 2b displayed the stronger fluorescence intensity and the highest fluorescence quantum yield (Φu=0.94) in these boron compounds. However, compounds 2c and 2d had the lower fluorescence intensity and quantum yield as a result of the heavy atom effect of the chlorine atom in the molecules.