Brightening of Long, Polymer-Wrapped Carbon Nanotubes By Large Scale sp³ Functionalization

Networks of long, polymer-sorted semiconducting single-walled carbon nanotubes (SWNTs) show excellent transport of both electrons and holes and are thus perfectly suited for electrically-driven light emission in the near-infrared (NIR) [1,2]. So far, their application in near-infrared light-emitting devices has been hampered by their low photoluminescence quantum yield (PLQY) and strong self-absorption owing to their small Stokes shift. In recent years, the controlled introduction of a low density of sp3 defects as exciton trapping sites was shown to lead to red-shifted emission with longer exciton lifetimes and improved PLQYs. However, due to the polarity of the employed diazonium salt reagent, this approach was limited to aqueous dispersions of SWNTs with often short tube lengths and the undesired presence of stabilizers. Here, we present a novel route to sp3 functionalization with diazonium salts in organic, non-halogenated solvents, thereby making it compatible with polymer-wrapped long SWNTs produced by shear force mixing. As a result of the low density of exciton quenching sites on shear mixed SWNTs [3], the excitons are efficiently channeled to the emissive defect sites, leading to absolute PLQYs of 4 % for functionalized (6,5) SWNT dispersions in toluene. This new method paves the way toward the large scale production of high-quality sp3 functionalized SWNTs and hence also thin films for optoelectronic devices with narrowband near-infrared emission. [1] Rother et al., ACS Appl. Mater. Interfaces 2016, 8, 5571-5579. [2] Brohmann et al., J. Phys. Chem. C 2018, 122, 19886-19896. [3] Graf et al., Carbon 2016, 105, 593-599. Figure 1