Understanding and Exploiting Redox in Conjugated Polymers: From Improved Polymer Conductivity, to Photoinduced Charge Transfer, to Next Generation Polymer Binders for Lithium Ion Batteries

Semiconducting polymer have the potential to be use in an exciting array of devices, but their intrinsic conductivity is

low due to their large band gaps. Chemically doping conjugated polymers is an effective way to increase conductivity

and involves introducing treating the polymer with a strong electron acceptor or donor that can undergo charge

transfer (i.e. redox) with the polymer. The charge transfer reaction creates delocalized electrical carriers on the

polymer chain (usually positive polarons a.k.a. holes) while the dopant molecules remain in the film and serves as a

counterion. Unfortunately, strong electrostatic attraction between counter-ions and most dopants will localize the

polarons and reduce their mobility. Here, we first explore a new family dopants based on substituted icosahedral

dodecaborane (DDB) clusters that provide a unique combination of high oxidizing potential and large size. By tuning

the cluster redox potential, we can understand the role of energetics in polymer conductivity, and the large size helps

reduce electrostatic interactions, resulting in polymer films with highly delocalized polarons and thus high

conductivity. A combination of molecular substituent tuning, electronic spectroscopy, and X-ray scattering are used

to under chemical-structure-function relationships. We next consider applications for doped conjugated polymers, in

this case focusing on electrochemically doped polymers and their application as binders in lithium ion batteries.

Battery binders are usually chosen only for chemical inertness, but the use of conjugated polymer binder can

increase overall conductivity and thus rate capabilities. By tuning the polymer redox to match the electrode material,

highly conductive doped binders can be produced, and by tuning the side chains, ionic conductivity can be mixed with

electronic conductivity, both of which are needed for fast battery operation. Finally, we end by examining self-

assembling amphiphilic conjugated polymers, and consider both photo-doping and chemical doping of these unique

water soluble polymers.