Diazaboryl-naphthyl-ketone: A New Scaffold with Bright Fluorescence, Aggregation-Induced Emission, and Application in the Quantitation of Trace Boronic Acids in Drug Intermediates.

This study describes the synthesis, structure, and photophysical properties of a new luminescent polyaromatic boronic acid scaffold, diazaboryl-naphthyl-ketones (DNKs). These stable compounds display extremely bright fluorescence, aggregation-induced emission, positive solvatochromism, and solid-state fluorescence. DFT calculations and X-ray crystallographic study revealed notable electronic and structural differences between these compounds and the parent diaminonaphthalene (DAN) adducts. Acylation of the DAN system causes a localization of both HOMO and LUMO onto the DNK unit, which validates the negligible influence of the B-aryl substituent. The LUMO energy is lowered, and its shape significantly altered. Photophysical data in solution and the solid state revealed blue-shifted, narrowed, and intense emissions for DNKs (up to 89 % quantum yield). The potential utility of the fluorogenic DNK system was demonstrated with a proof-of-concept for the determination of trace boronic acid contaminants in solid samples, down to one-ppm level, using HPLC with fluorescence detection. This method could be useful in pharmaceutical development for the quantitation of difficult-to-detect and potentially mutagenic residual boronic acid from late cross-coupling reactions in drug syntheses.