An Unconventional Mechanistic Insight on Aggregation Induced Emission in Novel Boron Dipyrromethenes and Their Rational Biological Realizations

Quinolone
and quinoline based boron dipyrromethenes (BODIPYs) viz.
BQN1 and BQN2 obtained by relative stabilization of keto and enol
forms of N-methylated quinolones via minute substitutional
variations (−H/–OCH3) have been reported.
The relative disparity in degree of aromaticity arising from quinolone/quinoline
strongly affects the free rotation of these molecules. The photophysical
and structural characteristics of these compounds revealed an exceptional
dissonance between restriction of intramolecular rotation (RIR) and
aggregation induced emission (AIE) signifying competitive steric hindrance
and conjugation. Despite being an AIE inactive dye, BQN1 experiences
maximum RIR and excels as a viscosity sensitive hindered molecular
rotor, while an effective J-aggregation irrevocably established AIE
in BQN2. This is the first report dealing with utilization of AIE
active BODIPY (BQN2) in fabrication of AIEgen loaded bovine serum
albumin (BSA) nanoparticles with live cell imaging in human breast
cancer cell line MDA-MB-231. Binding mode of human serum albumin (HSA)
to BQN2 has also been determined by molecular docking studies. In
addition, viscochromism of BQN1 has been visualized through apoptotic
marking in the MDA-MB-231 cell line.