Near‐Infrared Sensitized Photoinduced Atom‐Transfer Radical Polymerization (ATRP) with a Copper(II) Catalyst Concentration in the ppm Range

/tris(2-pyridylmethyl)amine (TPMA) as the catalyst, a polymethine as the photosensitizer, and α-bromophenylacetate as the alkyl halide initiator. Among the polymethines investigated with cationic, zwitterionic, or anionic structures, only the zwitterionic 2 exhibited sensitization activity under NIR light at room temperature resulting in the formation of polymers with controlled molecular weight characteristics and functionalities. The barbital group placed at the meso-position of 2 caused the activity in this photo-ATRP framework. The chain-end fidelity of the polymers was confirmed by chain extension and block copolymerization experiments. The polymerization system exhibits high photostability under NIR light exposure and irradiation dependency as demonstrated by light on/off experiments.