Charge Transfer from Photoexcited Semiconducting Single-Walled Carbon Nanotubes to Wide-Bandgap Wrapping Polymer

Abstract

As narrow optical bandgap materials, semiconducting single-walled carbon nanotubes (SWCNTs) are rarely regarded as charge donors in photoinduced charge-transfer (PCT) reactions. However, the unique band structure and unusual exciton dynamics of SWCNTs add more possibilities to the classical PCT mechanism. In this work, we demonstrate PCT from photoexcited semiconducting (6,5) SWCNTs to a wide-bandgap wrapping poly-[(9,9-dioctylfluorenyl-2,7-diyl)- alt -(6,6′)-(2,2′-bipyridine)] (PFO–BPy) via femtosecond transient absorption spectroscopy. By monitoring the spectral dynamics of the SWCNT polaron, we show that charge transfer from photoexcited SWCNTs to PFO–BPy can be driven not only by the energetically favorable E 33 transition but also by the energetically unfavorable E 22 excitation under high pump fluence. This unusual PCT from narrow-bandgap SWCNTs toward a wide-bandgap polymer originates from the up-converted high-energy excitonic state (E 33 or higher) that is promoted by the Auger recombination of excitons and charge carriers in SWCNTs. These insights provide new pathways for charge separation in SWCNT-based photodetectors and photovoltaic cells.

Evidence for a Polariton-Mediated Biexciton Transition in Single-Walled Carbon Nanotubes

“…For polymer-wrapped (6,5) SWCNTs in tetrahydrofuran, it was observed that the overall decay times were slightly elongated for excitation to higher excitonic levels such as the E 22 or E 33 . 47 The k 5 values should be essentially similar; however, the increased noise level at later times makes the fit less reliable, and the stated fit error likely underestimates the real uncertainty.…”

“…In case of UP excitation, the first two decays are about twice as fast as for E22 excitation. We attribute the slower decays for E22 excitation to the delay caused by the required internal relaxation to the E11 state (~ 100 fs) 47 and subsequent population of the UP by the dark polariton states. This evolution of the proposed UP to biexciton transition approximately follows the evolution of the LP feature (at 1.1 eV in Figure 3a and 3b).…”

“…[41][42][43][44] The large Coulomb interactions in one-dimensional nanotubes and the reduced dielectric screening enable many-body bound states such as trions or biexcitons. Trions are charged excitons that occur in doped nanotubes [45][46][47] but can also be created optically at high excitation intensities. 48 For (6,5) SWCNTs they show red-shifted (by 170-190 meV from the E11) absorption and emission.…”

Dendron–Polymer Hybrids as Tailorable Responsive Coronae of Single-Walled Carbon Nanotubes

“…Each corona phase can influence the fluorescence emission of the SWCNTs, due to its density and/or interactions with the SWCNT surface. Fluorescence emission of a certain chirality can be altered by the distinct dielectric environment that the corona phase induces around the SWCNTs or even charge transfer effects from the wrapping molecules to the SWCNT or vice versa. , Our PEG-dendrons are bound to the SWCNTs via end groups that differ in the type of their interaction with the graphene lattice. While π–π stacking of the SWCNT with the aromatic end groups is possible, hydrophobic interactions are expected in the case of the aliphatic end groups.…”

First-Principles Study on Tuning of Contact Electrification and Adhesion of Bio-inspired Adhesive Carbon-Based Materials via an External Electric Field

“…A carbon nanotube is a typical one-dimensional carbon material with excellent physical properties and has attracted tremendous attention in the past three decades since its discovery. − Carbon nanotube-based dry adhesive is one of the main routes for the fabrication of gecko-inspired artificial adhesives and has aroused research interests due to the material capability of achieving the real gecko structure. − The outstanding adhesion properties of carbon nanotubes (CNTs) are believed to originate from van der Waals (vdW) interactions at the micro- and nanoscale interface when contacting other surfaces . The vdW interaction mainly includes dipole–dipole, dipole–induced dipole, and dispersion interactions, which are essentially the electrostatic interactions between different charge centers. , Meanwhile, contact electrification will inevitably happen when two surfaces contact with each other and triboelectric charges are induced by electron transfer, ion transfer, or material transfer. − Contact electrification leads to the formation of a net positive charge on one surface and a net negative charge on the other.…”