Photophysical Study of Boron Difluoride Complex of 5-Hydroxyflavone Derivative
Anthony D’Aleo and Frederic Fages
The preparation and optical study of one new BF2-complex of 5-hydroxyflavone (1-BF2) is described. This complex is compared with two 2’-hydroxychalcone boron difluoride analogues. This dye was synthesized simply and exhibited in solution rather low photoluminescence quantum yield in the visible part of the spectrum. This complex, similarly to 2’-hydroxychalcone derivative (2-BF2), shows enhanced emission in the solid state (ten-fold increase). Complexation to boron difluoride was shown to affect differently the donor-acceptor character of these dyes, revealing a decrease of the excited state dipole moment for 1-BF2 and 2-BF2 while the one of 3-BF2 increases. Differences in the emission wavelength and efficiency in solid state were also noticed between BF2-complexes of 5-hydroxyflavone and 2’-hydroxychalcone. While for 1-BF2 and 2-BF2, an intense emission in the visible in recorded, for 3-BF2, an emission in the NIR (λem = 845nm) with low luminescence quantum yield is measured. It is suggested that the difference of emission wavelength is due to the difference of excited state dipole moment impacting strongly the intermolecular charge transfer state formed in the condensed phase.
Keywords: 5-hydroxyflavone, boron difluoride complex, solid-state fluorescence, photophysical study