Synthesis, structures and photophysical properties of boron–fluorine derivatives based on pyridine/1,8-naphthyridine

• Three boron–fluorine complexes containing heterocyclic rings were synthesized and structurally characterized.
• Two compounds exhibit strong fluorescent in the solid state, ascribed to weak intermolecular interactions.
• The fused/unfused benzene rings results in obvious changes of emissive quantum yields.
• The luminous molecule B3 could serve as a pH sensor with about 90-fold fluorescence ratio change upon protonated.

Three boron–fluorine complexes B1–B3 containing pyridine/1,8-naphthyridine were synthesized and structurally characterized. Compounds B1 and B2 exhibited strong fluorescence in solution and solid state. The solvent-dependent luminous properties and large Stokes shift in solution could be explained by intramolecular charge transfer, which is confirmed by time-dependent density functional theory calculation. The absolute quantum yield of B1 in powder form reached 0.48 because of inhibiting planar π⋯π stacking. Single-crystal X-ray diffraction analyses of B1 and B2 revealed that weak intermolecular C–H⋯F and H⋯π interactions hinder further stacking of π⋯π dimers, consequently preventing aggregation-induced quenching. Complex B3, composed of boron–dipyrromethene and 1,8-naphthyridine fluorophore, had potential applications as a pH ratiometric fluorescent sensor.

Three boron–fluorine complexes containing pyridine/1,8-naphthyridine were synthesized and structurally characterized, and two of them display intensive fluorescence in solution and solid state, the other composed of boron–dipyrromethene and 1,8-naphthyridine fluorophore can be used as a pH ratiometric fluorescent sensor.Figure optionsDownload as PowerPoint slide