Open-air green-light-driven ATRP enabled by dual photoredox/copper catalysis

Grzegorz Szczepaniak; Jaepil Jeong; Kriti Kapil; Sajjad Dadashi-Silab; Saigopalakrishna S Yerneni; Paulina Ratajczyk; Sushil Lathwal; Dirk J Schild; Subha R Das; Krzysztof Matyjaszewski

doi:10.1039/d2sc04210j

Open-air green-light-driven ATRP enabled by dual photoredox/copper catalysis

Chem Sci. 2022 Sep 20;13(39):11540-11550. doi: 10.1039/d2sc04210j. eCollection 2022 Oct 12.

Authors

Affiliations

¹ Department of Chemistry, Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA gszczepa@andrew.cmu.edu matyjaszewski@cmu.edu.
² Faculty of Chemistry, University of Warsaw Pasteura 1 02-093 Warsaw Poland.
³ Department of Biomedical Engineering, Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA.
⁴ Faculty of Chemistry, Adam Mickiewicz University, Uniwersytetu Poznańskiego 8 61-614 Poznań Poland.
⁵ Center for Nucleic Acids Science & Technology, Carnegie Mellon University Pittsburgh Pennsylvania 15213 USA.

Abstract

Photoinduced atom transfer radical polymerization (photo-ATRP) has risen to the forefront of modern polymer chemistry as a powerful tool giving access to well-defined materials with complex architecture. However, most photo-ATRP systems can only generate radicals under biocidal UV light and are oxygen-sensitive, hindering their practical use in the synthesis of polymer biohybrids. Herein, inspired by the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, we demonstrate a dual photoredox/copper catalysis that allows open-air ATRP under green light irradiation. Eosin Y was used as an organic photoredox catalyst (PC) in combination with a copper complex (X-Cu^II/L). The role of PC was to trigger and drive the polymerization, while X-Cu^II/L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X-Cu^II/L, generating Cu^I/L activator and PC˙⁺. The ATRP ligand (L) used in excess then reduced the PC˙⁺, closing the photocatalytic cycle. The continuous reduction of X-Cu^II/L back to Cu^I/L by excited PC provided high oxygen tolerance. As a result, a well-controlled and rapid ATRP could proceed even in an open vessel despite continuous oxygen diffusion. This method allowed the synthesis of polymers with narrow molecular weight distributions and controlled molecular weights using Cu catalyst and PC at ppm levels in both aqueous and organic media. A detailed comparison of photo-ATRP with PET-RAFT polymerization revealed the superiority of dual photoredox/copper catalysis under biologically relevant conditions. The kinetic studies and fluorescence measurements indicated that in the absence of the X-Cu^II/L complex, green light irradiation caused faster photobleaching of eosin Y, leading to inhibition of PET-RAFT polymerization. Importantly, PET-RAFT polymerizations showed significantly higher dispersity values (1.14 ≤ Đ ≤ 4.01) in contrast to photo-ATRP (1.15 ≤ Đ ≤ 1.22) under identical conditions.