Article Cite This: J. Phys. Chem. C XXXX, XXX, XXX−XXX
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Ultrafast Charge Transfer and Relaxation Dynamics in PolymerEncapsulating Single-Walled Carbon Nanotubes: Polythiophene and Coronene Polymer Arao Nakamura,*,† Ken-ichi Yamanaka,‡ Kenshi Miyaura,§ Hong En Lim,§ Kazunari Matsuda,∥ Boanerges Thendie,§ Yasumitsu Miyata,⊥ Taketo Kochi,# Susumu Okada,# and Hisanori Shinohara§ †
Toyota Physical and Chemical Research Institute, Nagakute 480-1192, Japan Toyota Central R&D Labs., Inc., Nagakute 480-1192, Japan § Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan ∥ Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan ⊥ Department of Physics, Tokyo Metropolitan University, Hachioji 192-0397, Tokyo, Japan # Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba 305-8571, Japan
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S Supporting Information *
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. SWNTs.3,4,7,14 Recently, we investigated the EET process in a paper-form sample of PFO-wrapped SWNTs and showed that ultrafast EET occurs in 0.38 ps, at a rate of ∼2.6 × 1012 s−1.14 The energy level alignment between poly(3-hexylthiophene) (P3HT) and SWNTs with large diameters is type I, whereas for small-diameter SWNTs (
