We report a structure-property study on phosphoryl-bridged viologen analogues with a remarkably low reduction threshold. Utilizing different benzyl groups for N-quaternization, we were able to confirm the p-benzyl substituent effect on the electronic tunability of the system while maintaining the characteristic chromic response of viologens with two fully reversible one-electron reductions. Due to the considerably increased electron-acceptor properties of the phosphoryl-bridged bipyridine precursor, N-benzylation was found to be very challenging and required the development of new synthetic strategies toward the target viologen species. This study also introduces a new and convenient way for the anion exchange of viologen systems by utilizing methyl triflate. Finally, the practical utility of the new species was verified in simplified proof-of-concept electrochromic devices.

Phosphorus-based materials have received widespread attention in recent years, in particular as possible candidates for practical application in organic electronics. The geometry and electronic nature of phosphorus make it a favorable heteroatom for property tuning in order to obtain better performing organic electronics. This Focus Review discusses recent structural modifications and syntheses of phosphorus-based materials, illustrates property tuning at the same time, and highlights specific examples for device applications.

A simple and representative procedure for the synthesis of N,N'-diarylated phosphaviologens directly from both electron-rich and electron-poor diaryliodonium salts and 2,7-diazadibenzophosphole oxide is reported. The latter are electron-deficient congeners of the widely utilized N,N'-disubstituted 4,4'-bipyridinium cations, also known as viologens, that proved to be inaccessible by the classical two-step route. The single-step preparation method for phosphaviologens described herein could be extended to genuine viologens but reached its limit when sterically demanding diaryliodonium salts were used. The studied phosphaviologens feature a significantly lowered reduction threshold as compared to all other (phospha)viologens known to date due to the combination of an extended π-system with an electron deficient phosphole core. In addition, a considerably smaller HOMO-LUMO gap was observed due to efficient π-delocalization across the phosphaviologen core, as well as the N-aryl substituents, which was corroborated by quantum chemical calculations. Detailed characterizations of the singly reduced radical species by EPR spectroscopy and DFT calculations verified delocalization of the radical over the extended π-system. Finally, to gain deeper insight into the suitability of the new compounds as electroactive and electrochromic materials, multicolored proof-of-concept electrochomic devices were manufactured.

of p-type or electron-donating materials, which have been well researched and include, but are not limited to, polyacetylenes, organosulfur compounds, paraquinones, tetracyanoquinodimethane, and polypyrrole composites. [ 6 ] While anode (n-type or electron-accepting) materials are far more rare in the fi eld of organic batteries, one particular class of compounds have appeared as potential candidates to develop fully organic and fl exible, lightweight batteries: compounds based on quaternized pyridine moieties, such as viologens (quaternized 4,4′-bipyridiniums). [ 7 ] Viologens are known to exhibit rapid and reversible electron transfers giving them great potential for use in a variety of applications such as, redox mediators, electrochromic devices, and now as electrode materials for organic batteries. Palmore and co-workers have recently reported a polymer anode material with pendant viologens, utilizing the fi rst reduction state of the viologen moieties for charge storage. [ 8 ] In 2011, our research group introduced a new class of viologen, the phosphaviologen, which is a phosphoryl-bridged 4,4′-bipyridine derivative with exceptionally strong electronaccepting properties. [ 9 ] Since the initial synthesis of the phosphaviologen scaffold, we have explored a variety of functionalizations at the nitrogen centers, including both benzyl [ 10 ] and aryl [ 11 ] substituents, to tune both the electronics and chromics of this species. With their enhanced electron-accepting properties (reduction thresholds 500 mV less than methylviologen for both reduction steps), we have chosen to investigate their properties as battery electrode materials.In this paper, we now report our initial contribution to the fi eld by applying our recently developed phosphaviologens P-MV and P-BnV ( Figure 1 ) as electrode materials in a hybrid organic/Li-ion battery setting. These initial studies focus on using the previously synthesized materials to test their viability as electrode materials in proof-of-concept devices via half-cell measurements versus Li-metal. While we do not provide large leaps in terms of overall capacity, our phosphaviologens (PV) utilize both redox steps in the charging/discharging cycles, allowing us to double the electron capacity per molecule compared to that of conventional viologens used as electrode materials. In an attempt to improve performance and stability, we have developed new synthetic methods to access phosphaviologen dimers, along with polymeric species that can be solution-processed as electrode materials in proof-of-concept Lithium-ion batteries are one of the most common forms of energy storage devices used in society today. Due to the inherent limitations of conventional Li-ion batteries, organic materials have surfaced as potentially suitable electrode alternatives with improved performance and sustainability. Viologens and phosphaviologens in particular, are strong electron-accepting materials with excellent kinetic properties, making them suitable candidates for battery applications. In this p...

Conjugated materials have attracted much attention toward applications in organic electronics in recent years. These organic species offer many advantages as potential replacement for conventional materials (i.e., silicon and metals) in terms of cheap fabrication and environmentally benign devices. While p-type (electron-donating or hole-conducting) materials have been extensively reviewed and researched, their counterpart n-type (electron-accepting or electron-conducting) materials have seen much less popularity despite the greater need for improvement. In addition to developing efficient charge transport materials, it is equally important to provide a means of charge storage, where energy can be used on an on-demand basis. This perspective is focused on discussing a selection of representative n-type materials and the efforts toward improving their charge-transport efficiencies. Additionally, this perspective will also highlight recent organic materials for battery components and the efforts that have been made to improve their environmental appeal.