Many of the electrochemical energy-storage systems under consideration for large-scale power storage and allocation rely on stable electroactive materials to shuttle and/or store charge. Here we seek to design a new class of organic compounds, based on the electroactive molecule phenothiazine, for use as (a) redox-shuttle additives to mitigate excess charge in overcharging lithium-ion batteries, and (b) catholyte materials for use in redox flow batteries. This presentation will include the results of density functional theory calculations that are used to model the physicochemical effects of substituent identity and placement on phenothiazine by introducing electron-donating and/or -withdrawing substituents at strategic positions around the heterocyclic core. Substituent crowding is shown to effect changes in oxidation potential at odds with those anticipated from Hammett constants, as well as changes in energetically optimal conformations, consistent with more-restricted relaxation pathways afforded by the additional steric strain. A subset of the compounds under consideration were subsequently selected for synthesis and electrochemical analysis. The results of this testing suggest that, unlike prior methods of increasing oxidation potentials using electron-withdrawing groups, strategic placement of substituents can be exploited to raise oxidation potentials without raising reduction potentials, thereby preventing access to reduction decomposition pathways. The results of this analysis reveal strategies for designing and tuning the properties of new electroactive compounds for energy-storage applications and beyond.