Insight into the enhanced performance of the 1-phenylethyl segment in an aza-BODIPY system

Non-aryl substituted aza-BODIPYs exhibit extraordinary optical properties. 1-Phenylethyl-substituted aza-BODIPY PE-BDP was herein successfully prepared. Based on X-ray crystallographic analysis, 1-phenylethyl segments at 1,7-sites in PE-BDP as a stable mesomer were observed for the first time, and the plane of the phenyl group in the 1-phenylethyl segment is orthogonal to the core of PE-BDP. This orthogonal structure enhanced the spin-orbit charge transfer intersystem crossing (SOCT-ISC), and PE-BDP could induce type-I ROS generation. By the cyclic voltammetry test of PE-BDP, the reduction-oxidation processes remained electrochemically reversible. Under alkaline conditions, the new dianion species generated from PE-BDP can be monitored by spectroscopic redshift, and theoretical calculations also supported this result. Self-assembled PE-BDP nanoparticles under irradiation exhibited a good tumor-inhibition capability by inhibiting proliferation and migration, and promoting the apoptosis of glioma cells by type-I ROS and photothermal effects.