Fusion of Aromatic Ring to Azoarenes: One-Pot Access to 5,6-Phenanthroliniums for Mitochondria-Targeted Far-Red/NIR Fluorescent Probes

Disclosed herein is a highly efficient strategy to fuse an aromatic ring to azoarenes for one-pot access to 5,6-phenanthrolinium skeletons via tandem ortho-C–H arylation and aryl quaternization. This protocol enables ortho-hindered azobenzenes to solely form 5-aryl-5,6-phenanthroliniums and ortho-unhindered azobenzenes to exclusively generate 5,7-diaryl-5,6-phenanthroliniums. The diarylated products (5k–5r) exhibit far-red to NIR emissions (678–742 nm) with large Stokes shifts, can specifically light up mitochondria in living cells, and, moreover, possess excellent photostability and low cytotoxicity.