Solid-emissive boron–fluorine derivatives with large Stokes shift

Novel BOPIM (boron 2-(2′-pyridyl)imidazole complex) derivatives with large Stokes shift were efficiently synthesized through two-step reactions, starting from commercially available 2-pyridinecarboxaldehyde and α-diketone. The dyes exhibit high fluorescent intensity in solution and also in solid state due to the intermolecular non-planar interactions. According to X-ray single crystal measurements, the non-covalent interactions (such as C–H⋯F–B, etc.) play important role in inhibiting planar π–π stacking, and the existence of terminal phenyl rings increases the electronic density of π system, which facilitates the charge transfer from the electron-donating π system to the electron-accepting boron moiety. DFT calculation based on X-ray crystallographic analysis was carried out for compound 2, giving consistent results with photophysical measurements.