Beyond the Hammett Effect: Using Strain to Alter the Landscape of Electrochemical Potentials. Issue 16 (21st June 2017)

• Record Type: Journal Article
• Authors: Casselman, Matthew D.; Elliott, Corrine F.; Modekrutti, Subrahmanyam; Zhang, Peter L.; Parkin, Sean R.; Risko, Chad; Odom, Susan A.
• Is Part Of: Chemphyschem. Volume 18:Issue 16(2017)
• Page Start: 2142
• Page End: 2146
• Publication Date: 2017-06-21
• Subjects: conjugation -- electronic structure -- redox chemistry -- strained molecules -- substituent effects; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201700607
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: The substitution of sterically bulky groups at precise locations along the periphery of fused‐ring aromatic systems is demonstrated to increase electrochemical oxidation potentials by preventing relaxation events in the oxidized state. Phenothiazines, which undergo significant geometric relaxation upon oxidation, are used as fused‐ring models to showcase that electron‐donating methyl groups, which would generally be expected to lower oxidation potential, can lead to increased oxidation potentials when used as the steric drivers. Reduction events remain inaccessible through this molecular design route, a critical characteristic for electrochemical systems where high oxidation potentials are required and in which reductive decomposition must be prevented, as in high‐voltage lithium‐ion batteries. This study reveals a new avenue to alter the redox characteristics of fused‐ring systems that find wide use as electroactive elements across a number of developing technologies. Abstract : Through the strategic placement of otherwise electron‐donating methyl groups at the positions ortho to nitrogen, planarization of the phenothiazine radical cation is prevented, thus raising the oxidation potential of this compound (blue) compared to its para ‐substituted isomer (green) and parent compound (black).