Effect of Polyelectrolytes on the Photoluminescence of Single-Walled Carbon Nanotubes-Experimental and Simulation Studies.

Hybrid nanoscale materials exhibit unique properties that are suitable for advanced technologies. To achieve a tunable material-property relationship, it is crucial to understand how these molecules assemble to form hybrid structures and the impact on an individual material's characteristics from such molecular assemblies. A hybrid material that comprises an optically active semiconducting single-walled carbon nanotube (SWCNT) and a polyelectrolyte could bring new opportunities for optoelectronic and nanophotonic materials. Here, we used a combined approach that included experimental observation and molecular dynamics (MD) simulations to investigate molecular assembly of an SWCNT-polyelectrolyte hybrid and the influence of the polymer on the nanotube's optical behavior. We report that sodium poly(styrenesulfonate) (PSS), an aromatic anionic polyelectrolyte, dispersed SWCNTs in water, but with exceptionally weak photoluminescence. MD simulations showed that PSS wrapped around the SWCNT via π-π interactions between the graphitic side walls on the SWCNT and aromatic substituents on PSS. Notably, the anionic group, which is directly attached to the aromatic ring on the polymer, is remarkably close to the nanotube surface. Accumulation of excessive negative charges could influence the exciton behavior on the nanotube and affect its photoluminescence. To gain further insight, we introduced a polycationic polyelectrolyte into the PSS-SWCNT complex to neutralize the charge and reduce net surface charge density on the SWCNT. Results showed a decrease in overall negative charge, evidenced from zeta potential measurements, and a subtle increase in the photoluminescence intensity upon cationic polyelectrolyte addition. Snapshots from MD simulation showed that the cationic polyelectrolyte decreased negative charges around the SWCNT in the PSS-SWCNT system. These results show that polyelectrolytes can influence the photoluminescence from SWCNTs through charge interaction. Understanding such polyelectrolyte-nanotube interactions could be essential in developing carbon-nanotube-based optical probes, sensors, and optoelectronic devices.