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

Abstract

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 incorporation of the [B−C] motif into a five-membered boramidine which exist 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 are expected to find application in a range of disciplines.