(Invited) Degradable Conjugated Polymer with Exceptional Selectivity for Large Diameter Semiconducting Carbon Nanotubes

Separation of electronically pure, narrow dispersed, pristine semiconducting single walled carbon nanotubes (S-CNT) from a heterogeneous as-synthesized mixture is essential for various semiconducting technologies and biomedical applications. While conjugated polymers are essential for this sorting step, it is highly desirable to remove any organic residues from the resulting devices. We report here the design and synthesis of a mild acid degradable π-conjugated polyimine polymer (PFO-N-BPy) that is structurally analogous to the commonly used and commercially available poly[(9,9-dioctylfluorenyl-2,7-diyl)- alt -co-(6,6’-(2,2’-bipyridine))] (PFO-BPy). An acid cleavable imine link (-HC=N-) was introduced in the PFO-N-BPy backbone to impart degradability, which is absent in PFO-BPy. PFO-N-BPy was synthesized via a metal catalyst free Aza-Wittig reaction in high yields. PFO-N-BPy with a degree of polymerization of just ~10 showed excellent (> 99% electronic purity) selectivity for both large diameter (1.3-1.7 nm) arc-discharge S-CNTs and smaller diameter (0.8-1.2 nm) HiPCO S-CNTs. Overall, selectivity for semiconducting species is similar to that of PFO-BPy but with an advantage of complete depolymerization under mild acidic conditions into recyclable monomers. We further show by UV-Vis, X-ray photoelectron spectroscopy (XPS), and SEM that the PFO-N-BPy wrapped S-CNTs can be aligned into a monolayer array on gate dielectrics using a floating evaporative self-assembly process from which the polymer can be completely removed. Short channel FETs were fabricated from the polymer-stripped aligned S-CNT arrays which further confirmed the semiconducting purity on the order of 99.9% or higher. We will present the recent optimized FET device results using this removable polymer.