Synthesis, spectral and electrochemical properties of selected boron ketiminates with aminocoumarin fragment

Six novel oxazaborines based on 7-aminocoumarin substituted by either fluoride or phenyl group on the boron atom were prepared from the corresponding enaminones. The compounds were characterized by means of 1H, 13C, 19F, and 11B NMR in solution, X-ray diffraction in crystal, UV–Vis spectroscopy, and electrochemistry. The observed optical properties were compared to the DFT calculations. Dynamic behaviour of selected oxazaborines was studied by means of 19F and 1H VT NMR and 2D EXSY. Both the enaminones and oxazaborines exhibit relatively strong fluorescence both in solid state and in frozen 2-methyltetrahydrofuran at 77 K, but none in solution. In some cases, phosphorescence was observed as well. Preliminary aggregation tests revealed aggregation induced emission (AIE) properties of the studied molecules. Concerning the electrochemical properties, the first reduction of all the oxazaborines studied proceeds as transport controlled one-electron (quasi)reversible process whereas the first oxidation of BPh2 oxazaborines proceeds as a two-electron irreversible process most probably of the ECE type. The oxidation of BF2 compounds was not possible to obtain within the given potential window. Analysis of frontier orbitals showed that change from BF2 to BPh2 leads to decrease of energy gap. .