A 1-hydroxy-2,3,1-benzodiazaborine-containing π-conjugated system: synthesis, optical properties and solvent-dependent response toward anions

Our interest in the functionalization of [sbnd]OH-substituted azaborines prompted us to synthesize a 1-hydroxy-2,3,1-benzodiazaborine conjugated with 1,8-naphthalimide 1. Its fluorescence was dramatically affected by the nature of the solvent. In particular, the use of DMSO, which has a relatively high donor number (DN = 29.8), led to a remarkable decrease in the fluorescence intensity (Φ_F = 0.0014), possibly due to intermolecular hydrogen-bonding interactions (Me₂S[dbnd]O⋯HO[sbnd]B). The presence of the hydroxyl group on boron led to a solvent-driven colorimetric response towards anions; high selectivity for F⁻ over other anions in DMSO, and responded to AcO⁻ and F⁻ in THF, as shown by UV/vis titrations, NMR, and mass spectroscopic analysis. The nucleus-independent chemical shift (NICS) indices suggested that hydrogen bonding interactions between Me₂S[dbnd]O and HO[sbnd]B reduced the aromaticity of the benzodiazaborine macrocycle, causing an increase in the negative character of the boron. The increase in the polarity of the B[sbnd]N bond may prevent acetate-binding of 1 in DMSO.