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New Approaches to Raising Redox Shuttle Oxidation Potentials

Tuesday, 30 May 2017: 10:40
Grand Salon D - Section 24 (Hilton New Orleans Riverside)
A. P. Kaur, S. A. Odom, S. Modekrutti, C. F. Elliott, C. Risko, S. R. Parkin, and M. D. Casselman (University of Kentucky)
The redox potentials of pi-conjugated organic molecules and polymers are essential factors that determine in part their performance in energy collection and storage applications. In these systems, the control of redox potentials usually involves substitution with electron-donating and/or electron-withdrawing groups, making use of the well-known Hammett constants as predictors of the extent of the change of redox potentials. An additional, less utilized route exploits strain-induced disruptions of π-conjugated frameworks by either (1) introducing bulky substituents to manipulate the dihedral torsions among the π-conjugated moieties or (2) to instill curvature into pi-conjugated networks. In each of these strained examples, the π-conjugated networks are strained in both the ground (neutral) and ionized (oxidized or reduced) electronic states. Taking these studies as inspiration, we sought to develop molecular design principles that impart strain in π-conjugated molecules in only one electronic state, enabling a new method to synthetically control redox potentials. This presentation will include on our approaches to raising oxidation potentials, including calculations, synthesis, electrochemical analysis, and – in some cases – cycling in overcharging lithium-ion batteries. A key highlight is the use of electron-donating alkyl groups to raise oxidation potentials – the opposite effect to what Hammett constants predict.