Nitration of a poly(fluorene- co -phenylene) backbone influences its selectivity for semiconducting versus metallic single-walled carbon nanotubes, and the regiochemistry of the nitro group has a significant impact.
The incorporation of single walled carbon nanotubes (SWNTs) into electronic devices requires electronically pure samples of either semiconducting or metallic SWNTs. Selective extraction of SWNTs by wrapping with electron-rich conjugated polymers has proven an effective method for producing samples enriched in semiconducting SWNTs. However, large-scale purification of metallic SWNTs with conjugated polymers has proven elusive. Here, we report SWNT dispersions prepared with three structurally similar poly(fluorene- co -phenylene) derivatives that possess varying degrees of nitration on the fluorene monomers. Differentiation of semiconducting and metallic SWNT populations was carried out by a combination of UV-Vis-NIR absorption, Raman, and fluorescence spectroscopy. We found that copolymers with meta -substituted nitro groups (with respect to the phenylene component) exhibit minimal inductive effects on the overall polymer backbone. When the nitro groups are ortho -substituted, a significant inductive effect occurs on the polymer backbone, resulting in a polymer that is more selective toward metallic SWNTs. The assessment of the inductive effects on the copolymer species was confirmed using Density Functional Theory (DFT) calculations. These results provide new insight into polymer design features, leading to the eventual goal of a conjugated polymer capable of selectively dispersing metallic SWNTs.