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

Seminar series
Organic Colloquium
Thu, Oct 21 4:00pm
Speaker Prof. Sarah Tolbert
Department of Chemistry & Biochemistry

Semiconducting polymer have the potential to be use in an exciting array of devices, but their intrinsic conductivity islow due to their large band gaps. Chemically doping conjugated polymers is an effective way to increase conductivityand involves introducing treating the polymer with a strong electron acceptor or donor that can undergo chargetransfer (i.e. redox) with the polymer. The charge transfer reaction creates delocalized electrical carriers on thepolymer chain (usually positive polarons a.k.a. holes) while the dopant molecules remain in the film and serves as acounterion. Unfortunately, strong electrostatic attraction between counter-ions and most dopants will localize thepolarons and reduce their mobility. Here, we first explore a new family dopants based on substituted icosahedraldodecaborane (DDB) clusters that provide a unique combination of high oxidizing potential and large size. By tuningthe cluster redox potential, we can understand the role of energetics in polymer conductivity, and the large size helpsreduce electrostatic interactions, resulting in polymer films with highly delocalized polarons and thus highconductivity. A combination of molecular substituent tuning, electronic spectroscopy, and X-ray scattering are usedto under chemical-structure-function relationships. We next consider applications for doped conjugated polymers, inthis 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 canincrease 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 withelectronic 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 uniquewater soluble polymers.