N-Heterocyclic Carbene-Carbodiimide (NHC-CDI) Adducts as a Platform for Highly Modular Redox-Active Organic Materials

Redox-active organic materials (ROMs) can provide more cost-effective and tunable alternatives to conventional metal-based energy storage systems. N-Heterocyclic carbene-carbodiimide (NHC-CDI) adducts provide a promising platform for these applications due to their modularity and zwitterionic nature. Of previously reported NHC-CDIs, only one has shown the necessary redox character for ROMs, but the CDI’s pyrene substituents limited its solubility, tunability, and synthetic accessibility. Herein, we report a simpler NHC-CDI framework for ROMs based on substituted diphenyl CDIs containing one dimethylamino group and one tunable handle. We synthesized six systematically varied adducts that undergo two sequential, reversible oxidations with half-wave potentials (E1/2,1 = −0.528 to −0.205 V; E1/2,2 = −0.005 to 0.115 V) correlating strongly to the electronics of the CDI (i.e., Hammett σp parameters). The most electrochemically-stable NHC-CDI had a theoretical capacity of 95 mAh g−1 and showed minimal changes in current density after ten cycles. Typically, achieving reversible two electron oxidations requires highly decorated p-type ROMs with extended π-conjugation; excitingly, the NHC-CDIs in this work can access this desired behavior via a “super radical stabilizer” instead of extended conjugation. The facile synthetic tunability and high solubility make this platform promising for the study and development of future ROMs.