Organic Four‐Electron Redox Systems Based on Bipyridine and Phenanthroline Carbene Architectures

Abstract

Novel organic redox systems that display multistage redox behaviour are highly sought‐after for a series of applications such as organic batteries or electrochromic materials. Here we describe a simple strategy to transfer well‐known two‐electron redox active bipyridine and phenanthroline architectures into novel strongly reducing four‐electron redox systems featuring fully reversible redox events with up to five stable oxidation states. We give spectroscopic and structural insight into the changes involved in the redox‐events and present characterization data on all isolated oxidation states. The redox‐systems feature strong UV/Vis/NIR polyelectrochromic properties such as distinct strong NIR absorptions in the mixed valence states. Two‐electron charge–discharge cycling studies indicate high electrochemical stability at strongly negative potentials, rendering the new redox architectures promising lead structures for multi‐electron anolyte materials.

Geometrical and Electronic Structure of Cation Radical Species of Tetraarylanthraquinodimethane: An Intermediate for Unique Electrochromic Behavior

“…Organic redox systems undergo reversible electron transfer when the resulting charged species are stable enough [1–5] . Charge delocalization and/or formation of additional aromatic ring upon electron transfer are often adopted strategies to stabilize the organic ions [6–15] . Quinodimethanes are the cross‐conjugated π‐systems, [16,17] which are suitable scaffolds to design the reversible redox systems, especially because of the formation of planar π‐skeleton with an additional aromatic ring in the corresponding ion radicals and doubly‐charged ions [18–20] …”

“…[1][2][3][4][5] Charge delocalization and/or formation of additional aromatic ring upon electron transfer are often adopted strategies to stabilize the organic ions. [6][7][8][9][10][11][12][13][14][15] Quinodimethanes are the crossconjugated π-systems, [16,17] which are suitable scaffolds to design the reversible redox systems, especially because of the formation of planar π-skeleton with an additional aromatic ring in the corresponding ion radicals and doubly-charged ions. [18][19][20] Based on the general consideration shown above, the pentacenequinodimethane-type dication (I 2 + ) has a quite peculiar structure, in which the two positive charges are located on the one side of the molecular skeleton (Scheme 1a).…”

Persistent Radicals Derived from N-Heterocyclic Carbenes for Material Applications

“…The remarkable stability of organic and organometallic radicals derived from NHCs has attracted recent attention as energy storage materials in various battery systems (Figure ). ,,, Radicals stabilized by NHCs are suitable in battery electrolytes due to their high redox reversibility. In this section, we demonstrate the potential of new organic and organometallic radicals stabilized by NHCs in battery anolytes.…”

A bis-NHC–CAAC dimer derived dicationic diradical

“…Electronically related to TTF, in recent years several carbene-based electron-rich alkenes have been synthesized, 10–14 such as the NHC-CAAC dimer V 11 (Scheme 1). These compounds exhibit two reversible one-electron redox processes and all three oxidation states can be isolated: neutral, radical cation, and dication, similar to I and II .…”