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FIP Seminar: Opto-electronic and Excited-State Dynamical Properties of Polymer-Wrapped Single-Walled Carbon Nanotube Superstructures

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Wednesday, November 08, 2023
12:00 pm - 1:00 pm
Dr. Michael J. Therien, William R. Kenan, Jr. Distinguished Professor of Chemistry, Duke University

Charged, chiral anionic semiconducting polymers helically wrap single-walled carbon nanontubes (SWNTs) at periodic and constant morphology (Figure 1a-b). These polymers can be to modulate SWNT electronic properties, provide expansive solubility, or organize functional organic moieties at predefined intervals along the SWNT surface. Such helically wrapped polymer-SWNT superstructures, for example, feature perylene diimide (PDI) electron acceptor unit positioned at 3 nm intervals along the nanotube surface, thus controlling rigorously SWNT-electron acceptor stoichiometry and organization. Potentiometric studies determine driving forces for photoinduced charge separation (CS) and thermal charge recombination (CR) reactions, as well as spectroscopic signatures of SWNT hole polaron and PDI radical anion states. Femtosecond pump-probe transient absorption spectroscopic experiments detail driving force- and solvent-dependent photoinduced CS and thermal CR dynamics, and provide insights into the factors that govern photoinduced charge transfer reactions at soft matter-hard matter interfaces defined by polymers and SWNTs (Figure 1c). Related systems in which a rigid polymer wraps a metallic nanotube surface modifies the energy-momentum (E-k) dispersion (band structure) of the tube, driving a metallic-to-semiconductor phase transition. This strategy contrasts approaches that regulate electronic structural properties of bulk-phase materials which rely on altering the nature of covalent bonding. Electronic spectral, chiro-optic, potentiometric, electronic device, and work function data corroborate that the magnitude of band gap opening depends on the nature of the polymer electronic structure. Polymer dewrapping reverses the conducting-to-semiconducting phase transition, restoring the native metallic carbon nanotube electronic structure. Because the energy separation between carbon nanotube valence and conduction bands depends on the polymer electronic structure, this approach provides a new approach to realize novel low band gap one-dimensional materials by design.

Contact: August Burns