Literature Seminar – Organocatalyzed atom transfer radical polymerization (O-ATRP) is a reversible deactivation radical polymerization method that employs organic photoredox catalysts (PCs) and visible light to produce well-defined polymers. The use of organic PCs allows for polymerizations to occur under mild and energy-efficient conditions without use of rare-earth metals. Understanding the correlation between excited-state photophysical properties and PC performance in O-ATRP is critical to designing effective catalysts, which leads to improved polymerization outcomes. In this presentation, a recent publication by the Orr-Ewing group that investigates excited-state photophysical properties of dihydrophenazine and phenoxazine PCs is discussed.1 This work challenges traditional hypotheses that long excited-state lifetimes and charge transfer states, which are thought to promote intersystem crossing, are critical parameters for superior PC performance. This research is then placed in context relative to other recent publications in the field2, 3 as well as unpublished work, in which time-resolved spectroscopy has been used to characterize various organic PCs employed in O-ATRP.
REFERENCES
1) Bhattacherjee, A.; Sneha, M.; Lewis-Borrell, L.; Amoruso, G.; Oliver, T. A. A.; Tyler, J.; Clark, I. P.; Orr-Ewing, A. J. Singlet and triplet contributions to the excited-state activities of dihydrophenazine, phenoxazine, and phenothiazine organocatalysts used in atom transfer radical polymerization. J. Am. Chem. Soc. 2021, 143 (9), 3613-3627.
2) Lattke, Y. M.; Corbin, D. A.; Sartor, S. M.; McCarthy, B. G.; Miyake, G. M.; Damrauer, N. H. Interrogation of O-ATRP activation conducted by singlet and triplet excited states of phenoxazine photocatalysts. J. Phys. Chem. A 2021, 125 (15), 3109-3121.
3) Sneha, M.; Bhattacherjee, A.; Lewis-Borrell, L.; Clark, I. P.; Orr-Ewing, A. J. Structure-dependent electron transfer rates for dihydrophenazine, phenoxazine, and phenothiazine photoredox catalysts employed in atom transfer radical polymerization. J. Phys. Chem. B 2021, 125 (28), 7840-7854.