Synthesis, photophysical and electrochemical properties of aza-boron-diquinomethene complexes

A series of aza-boron-diquinomethene (aza-BODIQU) complexes with different aryl-substituents (B1-B6) were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. All complexes exhibit strong ¹π-π* absorption bands and intense fluorescent emission bands in the visible spectral region at room temperature. The fluorescence spectra in solution show the mirror image features of the S₀→S₁ absorption bands, which can be assigned to the ¹π-π*/¹ICT (intramolecular charge transfer) emitting states. Except for B6, all complexes exhibit high photoluminescence quantum yields (Φ_PL = 0.47-0.93). The spectroscopic studies and theoretical calculations indicate that the photophysical properties of these aza-BODIQUs can be tuned by the appended aryl-substituents, which would be useful for rational design of boron-fluorine complexes with high emission quantum yield for organic light-emitting applications.