Supramolecular interactions of fluorene-based copolymers containing 3,4-propylenedioxythiophene and phenazine units with SWNTs

Abstract

Selective interactions between conjugated polymers and single-walled carbon nanotubes (SWNTs) are promising for purifying and isolating electronically enriched nanotube structures. However, the structure–property relationships that dictate the interaction selectivity are still poorly understood. Here, two different fluorene-based conjugated copolymers, poly[(9,9′-dioctylfluorene)-alt-(3,3-didodecyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)] (PFO-ProDOT), and poly[(9,9′-dioctylfluorene)-alt-(2,3-didodecyloxyphenazine)] (PFO-DPZ), were synthesized by the palladium-catalyzed Suzuki cross-coupling polymerization. These polymers differ in their structure and electronic properties, with PFO-ProDOT being relatively electron rich, and PFO-DPZ being relatively electron poor. Both polymers were able to form stable supramolecular complexes with SWNTs in common organic solvents, such as tetrahydrofuran (THF), toluene, and xylene. These complexes were characterized by UV-Vis-NIR absorption, Raman, and fluorescence spectroscopy, as well as by thermogravimetric analysis. Analysis of UV-Vis-NIR absorption and Raman data indicates that PFO-ProDOT is more selective for semiconducting SWNTs, while PFO-DPZ exhibits some preference for metallic SWNTs. Thus, a combination of conjugated polymer structure and electronics impacts selectivity for the different types of SWNTs present in commercial samples.