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

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.