Ultrafast Charge Transfer and Relaxation Dynamics in Polymer-Encapsulating Single-Walled Carbon Nanotubes: Polythiophene and Coronene Polymer

Abstract

We investigate the photophysical properties of polymer-encapsulating single-walled carbon nanotubes (SWNTs) using absorption spectroscopy, photoconductivity spectroscopy, and femtosecond pump−probe spectroscopy. In a polythiophene (PT)-encapsulating SWNT film, one or two PT layers are encapsulated within SWNTs, depending on the tube diameter. For single encapsulated PT layers, the photoconductivity action spectrum shows a large photocurrent signal corresponding to absorption bands associated with PT exciton and continuum states, indicating charge transfer between the PT and the small-diameter SWNT. Pump−probe measurements show that electron transfer to the SWNT occurs in 0.53 ps and electrons then recombine with holes remaining in the PT in 11 ps. In a coronene-polymer-encapsulating SWNT film, weak absorption bands at 1.7 and 3.4 eV are observed in addition to the SWNT spectrum. Band calculations allow these to be assigned to optical transitions between the electronic states originating from the coronene polymer, hybridized with those of the SWNT. The pump−probe measurements reveal fast electron relaxation (0.38 ps) from the conduction band of the coronene polymer to the lowest conduction band originating from the SWNT and subsequent recombination (1.5 ps) of these electrons with holes in the top valence band originating from the coronene polymer.

Coronenes, Benzocoronenes and Beyond: Modern Aspects of Their Syntheses, Properties, and Applications

“…Yet, in some other cases, coronene was found to build ordered and disordered packings in the carbon nanotubes, [185–186] resulting in graphene nanoribbons, [187] inner tubes, peapods [188] and others, depending on the conditions used to incorporate coronene in nanotubes. The ultrafast charge transfer and relaxation dynamics of polythiophene and coronene polymer‐encapsulated nanotubes have been studied, [189] while coronene molecules in carbon nanotubes [190] also offer a high charge carrier mobility of 14.93 cm 2 V −1 s −1 . In other studies, coronene composites with carbon nanotubes showed a bright photoluminescence [191] …”

Hole Doping in Polythiophenes Encapsulated in Semiconducting and Metallic Single-Walled Carbon Nanotubes: Impact of the Electronic Structure

“…Thus, the molecules are closely attached to the surfaces of the SWNTs on either the inside or outside. As pointed out in ref , the van der Waals bonding between the SWNT and the wrapping molecule has a similar nature to that between the SWNT and the encapsulated molecule. Theoretical calculations showed that ionization potentials of PT molecules on the inside of SWNTs with diameters of 0.9–1.7 nm were about 0.1 eV larger than that of the isolated PT .…”

Atomic pseudopotentials for reproducing π‐orbital electron behavior in sp2 carbon atoms

“…In a recent work, Nakamura et al have studied the photoexcitation spectrum of a coronene polymer encapsulated in a carbon nanotube . In this work, they show that two absorption bands (at around 1.7 and 3.4 eV) are due to a charge transfer from the coronene polymer to the nanotube.…”