Rigid π-Extended Boron Difluoride Complex with Mega-Stokes Shift for Bioimaging.

The rational design of a rigid π-extended ligand, suitable for the formation of four-coordinate boron complexes, has led to the synthesis of the fused hexacyclic structure of carbazolo[2,1-]phenanthridine. The photophysical characterization of the novel fluorophore revealed a significant Stokes shift whose intramolecular charge transfer origin has been corroborated by computational calculations. The usefulness of the reported -difluoroboryl complex as fluorescent probe with large Stokes shift has been demonstrated for cancer cells imaging.