Synthesis, NMR, X-ray and UV/Vis characterization and preliminary luminescence study of some boron β-iminoenolates having 6-aminocoumarin moiety

Five coumarin-based polarized ethylenes (enaminoketones, enaminoester and enaminoamide) were prepared using the condensation of the parent β-dicarbonyl compounds with 6-aminocoumarin. Reaction of the polarized ethylenes with an appropriate source of trivalent boron gave corresponding boron β-iminoenolates having either BF2 or BPh2 fragment. The prepared iminoenolates were characterized by means of multinuclear magnetic resonance in solution, single-crystal X-ray diffraction and UV/Vis spectroscopy. A preliminary luminescence study of the iminoenolates as well as their parent enamines was done. The compounds exhibited fluorescence in a solid state as well as in a frozen 2-methyltetrahydrofuran at 77 K. Exploratory tests showed promising AIE/AIEE properties of the tested compounds. On the other hand, no fluorescence in a solution state (with one exception) was observed.

Graphical abstractBoron β-iminoenolates having coumarin-6-yl moiety on the nitrogen atom and BF2 or BPh2 fragment fluoresce both in solid state and in frozen 2-methyltetrahydrofuran at 77 K. No fluorescence was observed in solution. The fluorescence starts to appear in aggregation state after admixing their THF solutions with water.Figure optionsDownload full-size imageDownload as PowerPoint slide