Functionalization Of Poly(3-hexylthiophene-2,5-diyl) For Nanoelectromechanical Devices

Innovative nanoelectromechanical (NEM) switches are being developed to reduce device actuation voltages as well as to avoid adhesion, which results in device failures. Minimizing leakage currents and increasing device longevity are additional goals of this technology. Unlike traditional electromechanical switches, which rely on direct contact of the electrodes, these switches contain a nanometer-scale organic thin film between two electrodes. The current is modulated by compressing the film, which decreases the gap to a dimension where tunneling between the two electrodes occurs. Conversely, the switch is turned off by the restoring force of the organic layer that returns the gap to its original distance. We term this squeezable switch a “squitch”. The properties of the squitch are highly dependent on the organic material sandwiched between the electrodes. Modified poly(3-hexylthiophene-2,5-diyl) (P3HT) was explored for the design of this organic layer due to its conductive properties and previous use in devices. A simple, two-step, post-polymerization procedure developed in the Swager group was used for the modification of P3HT. This procedure involves bromination of P3HT with N-bromosuccinimide followed by lithium-halogen exchange and quenching of the anion with an electrophile. Through this work we found that anhydrides were the electrophile of choice to yield ketone-modified P3HT. Several functional groups, including long, branched, and unsaturated alkyl chains, trimethylsilyl, and triisopropylsilyl groups were installed on P3HT by varying the anhydride structure. Additionally, a para-substituent study of synthesized benzoyl-modified P3HT was conducted to gain insight into how the ketone modification alters the properties of the polymer.