Boramidine: A Versatile Structural Motif for the Design of Fluorescent Heterocycles

Sodium cyanoborohydride-derived N-alkyl­nitrilium­boranes were found to be versatile precursors for the synthesis of novel boron-containing heterocycles. The reaction between N-alkyl­nitrilium­boranes and 2-aminopyridines, imidazoles, oxazoles, or isoxazoles leads to the incorporation of the [B–C] motif into a five-membered boramidine, which exists as a mixture of Z and E isomers. The resulting heterocycles are blue fluorescent in both the solid state and in solution with ca. 2700–8400 cm–1 Stokes shifts and quantum yields in the 65–74% range in water and in the 42–84% range in organic solvents. The combination of photophysical properties, structural tunability, stability, and solubility in various media is expected to find application in a range of disciplines.