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.