Specific Active Sites of Organo-Photocatalysts for Photo-Atom Transfer Radical Polymerization: A Combined Experimental and Theoretical Study of N-Unsubstituted Diketopyrrolopyrrole

Organocatalyzed atom transfer radical polymerization (O-ATRP) with light, acting as photoredox catalysis, is growing to be one of the emerging fields of photocatalysis and chemical transformations due to the mild, environment-friendly, and light-control manners. To screen much more effective metal-free photocatalysts and the exact functions of different fragments in organic molecular photocatalysts, this report selected N-unsubstituted diketopyrrolopyrrole (DPP) analogues and figured out the structure- properties relationship and the catalytic mechanism. The results revealed the key role of the N-unsubstituted DPP core in the charge transfer, singlet/triplet formation, and intermediate formation. Furthermore, the DPP core acted as the function of reductive reaction initiators with reductive potentials, while the adjacent groups tuned oxidative potentials and stability of the radical cations and simultaneously controlled the oxidative quenching deactivation process through the bromide (-Br) intermediates of doublet complexes. The systematic inspection of the atomic active sites of photoredox catalysts has so far not been taken into consideration regarding both the experimental and theoretical examination. The findings about these novel DPP photoredox catalysts will aid in the rational search for much more effective organo-photoredox metal-free compounds for use in controlled radical polymerization and other organic transformations.

Automated summary

Organocatalyzed atom transfer radical polymerization (O-ATRP) with light as photoredox catalysis is an emerging field of photocatalysis and chemical transformations. This study investigated the key role of N-unsubstituted diketopyrrolopyrrole (DPP) analogues in charge transfer, singlet/triplet formation, and intermediate formation, providing insights into the structure-properties relationship and catalytic mechanism. The findings contribute to the rational search for metal-free photocatalysts for controlled radical polymerization and other organic transformations.