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

Abstract

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-c]­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 N,N-difluoroboryl complex as fluorescent probe with large Stokes shift has been demonstrated for cancer cells imaging.

Synthesis and Characterization of Boron Difluoride Complexes Bearing π-Expanded Pyridine Ligands as Organic Fluorochromes

“…While the dipyrromethene, the ligand of BODIPY, has a highly symmetric structure derived from dipyrrole, the design of the novel ligands based on the desymmetrization with the expansion of the π-conjugated system could be a powerful approach to achieve unique optical properties. In recent years, various groups have reported the enlarging the Stokes shift of boron complexes by using nonsymmetric ligands such as anilido-imine and pyridine, benzo-fused dipyrromethene, and carbazole­[2,1- c ]­phenanthridine . Moreover, applying ligands with intramolecular charge transfer (ICT) character was often useful for the bathochromic shift of emission bands .…”

Going beyond the borders: pyrrolo[3,2-b]pyrroles with deep red emission

“…The lengths of the newly formed B-C bonds are 1.6 Å, which is a slightly shorter value than those reported for related compounds and suggests a stronger bond, 35,55 while the lengths of the B-N bonds are 1.63 Å, which is similar to the B-N bond length found in analogous compounds 55 and BODIPY-type molecules. 56 Van der Waals interactions govern the crystal packing, with the main structural motif being the interaction of bent C8 aliphatic chain with two phenyl substituents attached to the boron atom adjacent to the same molecule and then with the octylphenyl substituent attached to the nitrogen atom of the neighboring molecule. No obvious -stacking interactions are observed, probably due to the orientation of phenyl substituents on the boron atom that prevents these heteroacenes with extended  systems from approaching each other.…”

2‐(Quinol‐8‐yl)pyrrole‐Boron Difluoride Complexes, Simple and Tractable Structures Exhibiting Red Emission

“…The strategy based on the desymmetrization with expansion of the π‐conjugated system of ligands is a powerful approach to achieve large Stokes shift‐values [13] . In particular, several N , N ‐ligands consisting of donor and acceptor sides have been studied toward red emission properties ascribed from the intramolecular charge transfer (ICT) character [13b,c,e,14] . In 2005, Wang et al.…”