Impact of Conjugated Polymer Characteristics on the Enrichment of Single-Chirality Single-Walled Carbon Nanotubes

Polymer characteristics influence the chiral selectiv-ity and yield in the enrichment of (7,6) from Signis SG76 in toluene by various fluorene homopolymers and copolymers. Fluorene homopolymers such as poly(9,9-di-n-dodecylfluorene) (PFDD) and copolymers with anthracene such as poly[(9,9-dihexylfluorenyl-2,7-diyl)-co-(9,10-anthracene)] (PFH-A) result in high (7,6) selectivities of up to 67 and 72%, respectively. The selectivity is calculated by optical absorption using a known extinction coefficient and also evaluated by Raman scattering and photoluminescence excitation. In contrast, poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(9,10-anthracene)] (PFO=A), with a double-bond spacer, results in (9,5) dominant extractions with the purity of (9,5) up to 80% after ultracentrifugation, which is believed to be the first report on the successful enrichment of (9,5) by conjugated polymers. The chiral selectivity is also greatly impacted by the length of alkyl side chain of fluorene homopolymers: hexyl group has low selectivity, while octyl, dodecyl, and tetradecyl (PFTD) groups show high selectivity toward (7,6), and the octadecyl group is prone to include bigger tubes. Interestingly, a chiral selection transition from (7,6) to (8,6) occurred using PFTD after a few enrichment cycles. The chiral purity of (8,6) was greatly improved from 50 to 86% after slow filtration. Polymer molecular weight (MW, here PFDD) also plays a role in the selectivity and yield. Low MW leads to a low yield, and high MW leads to a low selectivity, with the optimal range (Mn) being ca. 20-35 kDa when the polydisperse index is ca. 2-3. Molecular dynamics simulation confirms that different lengths of side chain of polyfluorene have different wrapping stabilities toward specific chirality, where PFTD shows greater stability toward (8,6) than (7,6).