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

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–CuII/L). The role of PC was to trigger and drive the polymerization, while X–CuII/L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X–CuII/L, generating CuI/L activator and PC˙+. The ATRP ligand (L) used in excess then reduced the PC˙+, closing the photocatalytic cycle. The continuous reduction of X–CuII/L back to CuI/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–CuII/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.


Instrumentation
Nuclear Magnetic Resonance (NMR) 1 H NMR spectra were recorded on Bruker Avance III 500 MHz spectrometers with D2O or DMSO-d6 used as the solvent.

Size Exclusion Chromatography (SEC)
SEC measurements of p(OEOMA500) were performed using PSS columns (Styrogel 10 5 , 10 3 , 10 2 Å) with DMF as an eluent at 50 °C and the flow rate of 1 mL/min. Linear poly(methyl methacrylate) standards were used for calibration. SEC measurements of poly(methyl acrylate) were conducted using PSS columns (Styrogel 10 2 , 10 3 , 10 4 , 10 5 Å) with THF as an eluent at 35 °C and the flow rate of 1 mL/min. Linear poly(methyl methacrylate) standards were used for calibration.

Supplementary Information
Size Exclusion Chromatography with Multi-Angle Light Scattering (SEC-MALS) SEC-MALS measurements of polymers and bioconjugates were performed using Agilent SEC system (Agilent, 1260 Infinity II with UV detector) coupled with MALS, DLS, Viscometer and RI detectors (Wyatt Technology, USA). Measurements were performed using Waters Ultrahydrogel Linear column with 1X DPBS as an eluent at rt and the flow rate of 0.5 mL/min.

Fluorescence Quenching Experiments
Emission measurements were performed in a four-window 1x1 cm path length quartz microcuvette (ThorLabs) using a Edinburgh Instruments FS5 spectrophotometer.

DNA Synthesis
The model DNA initiator (T10-iBBr) was synthesized following the previously reported protocol in the MerMade 4 oligonucleotide synthesizer (Bioautomation). 1

Oxygen measurements
Oxygen measurements were performed using FireStingGO2 pocket oxygen meter and a solvent-resistant oxygen probe purchased from PyroScience.

Polymerizations
Polymerizations were carried out in open-to-air vials under green LEDs purchased from aspectLED (520 nm, 9.0 mW/cm 2 ). The LED strips were mounted inside a glass container (diameter = 9 cm, height = 7 cm). Polymerizations in the presence of cells were carried out in a 96-well plate using the Lumidox 96-Well Green LED Array (520 nm, 20.0 mW/cm 2 ).

Procedures
General Procedure for EY/Cu-catalyzed ATRP of OEOMA500 Prior to polymerization, stock solutions of HOBiB (15.8 mg in 1.0 mL DMSO), CuBr2 (33.5 mg in 20.0 mL DMSO), TPMA (13.1 mg in 1.0 mL DMSO) and EYH2 (9.7 mg in 10 mL DMSO) were prepared ( Figure S1A). The ATRP cocktail was then prepared as follows. In a 5 mL volumetric flask, 750 mg of OEOMA500 was weighed ( Figure S1B). CuBr2 stock (200 µL), TPMA stock (100 µL), HOBiB stock (100 µL), EYH2 stock (50 µL), DMSO (50 µL) and 10X PBS solution (500 µL) were then added ( Figure S1C). Finally, water was added to the mark on the volumetric flask, and the reaction mixture was stirred on a vortex ( Figure S1D (Table S1) The ATRP cocktail (5 mL) with a target DP = 1000 was prepared according     The assumption that the hydrodynamic volumes of two polymers eluting at the same chromatographic retention time are assumed to be identical and thus leads to equation 4.

Equation 4
Rearranging equation 4 gives the molecular weight M2 of the analyte. Supplementary Information 18 Rewriting Equation (4) serves to establish a linear relationship between the logarithm of the molecular weight of one polymer (a standard) and that of another polymer, which after plotting gives a slope and intercept that can be converted to the MH parameters.
The molecular weight of p(OEOMA500) was determined by multi angle light scattering (MALS). The PMMA molecular weights and p(OEOMA500) molecular weights used for the determination of the MH parameters are listed in Table S2 and plotted in Figure S5. Using equation 5, these MH parameters give good estimates of the p(OEOMA500) molecular weight (Table S2).