(Invited) Excited-State Dynamical Studies of Positively and Negatively Charged Excitons in Polymer-Wrapped Single-Walled Carbon Nanotube Superstructures

Wednesday, 31 May 2017: 09:20
Churchill B1 (Hilton New Orleans Riverside)
Y. Bai, J. H. Olivier, G. Bullard, and M. J. Therien (Dept. of Chemistry, Duke University)
Conjugated, highly charged aryleneethynylene polymers exfoliate, individualize, and disperse single-walled carbon nanotubes (SWNTs) via a single-chain helical wrapping mechanism. These semiconducting polymer-SWNT superstructures are robust in a wide range of aqueous and organic solvents, maintaining a fixed polymer helical pitch length on the SWNT surface; importantly, this single chain polymer wrapping of the SWNT surface solubilizes the nanotube at a minimal polymer:SWNT molar ratio, and provides a facile means to organize functional organic moieties at predefined intervals along the SWNT surface. We have investigated the transient absorptive and dynamical properties of positively and negatively charged excitons (i.e., hole- and electron-trions) in these semiconducting polymer-wrapped SWNT superstructures. This work exploits redox titration experiments that fix SWNT electron or hole polaron concentrations, and ultrafast pump-probe transient spectroscopic measurements that determine trion transient absorptive signatures and dynamics as functions of absolute electron- or hole-doping levels. Global analysis of these data over the entire vis-NIR spectral domain, where these systems display characteristic transient absorptive spectral signatures, provide fundamental new understanding of trion formation and decay mechanisms in semiconducting SWNTs essential for developing electro-optic and photonic materials.

Figure. (A) Structural schematic of a chiral aryleneethynylene polymer-wrapped SWNT. (B) Molecular structure of the binaphthalene-based conjugated, polyanionic semiconducting polymer, S-PBN(b)-Ph5. (C) Schematic illustration highlighting semiconducting SWNT hole polaron, exciton, positively charged exciton (hole-trion) states.