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 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 (ΦF = 0.0014), possibly due to intermolecular hydrogen-bonding interactions (Me2SO⋯HOB). 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 Me2SO and HOB reduced the aromaticity of the benzodiazaborine macrocycle, causing an increase in the negative character of the boron. The increase in the polarity of the BN bond may prevent acetate-binding of 1 in DMSO.

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