Coumarin-Based Boron Complexes with Aggregation-Induced Emission

Two coumarin-based boron complexes (HBN and MBN) with aggregation-induced emission were designed and synthesized. The photophysical properties of the complexes were investigated in different solvents and in the solid state. Results showed that the inhibited C=N isomerization by N,O-chelated BF₂ caused the significant enhancement of fluorescence in THF. In particular, the complexes displayed red-shifted emissions (>60 nm) in mixed solvents of CH₃CN and water because of the aggregation-induced charge-transfer enhancement. In the solid state, the bright red emission appeared at 650 nm (620 nm), with a Stokes shift of 170 nm. Cell-imaging experiments indicated that the complexes have good membrane permeability and can be used as lysosome trackers.