Boron difluoride complexes of 3-hydroxyflavone derivatives: efficient bioinspired dyes for solution and solid-state emission

A series of six boron difluoride complexes of 3-hydroxyflavone derivatives is described. These dyes were synthesized very simply and exhibited bright visible emission in solution (up to unity) as well as emission in the solid state. Complexation to boron difluoride was shown to impart donor-acceptor character to the excited state of these dyes, which further shifted the emission towards the visible part of the spectrum. Furthermore, differences were noticed following the strength of the donor and the acceptor. Light emission from the pi-stacked molecules was quenched relative to the solution behaviour which was interpreted in terms of both packing and electronic properties of the molecular dyes. The packing arrangement was found to be a function of the substituent on the 3-hydroxyflavone derivatives.