Extending π-electron systems are among the most important topics in physics, chemistry and materials science because they can result in functional materials with applications in electronics and optics. Conventional processes for π-electron extension, however, can generate products exhibiting chemical instability, poor solubility or disordered structures. Herein, we report a novel strategy for the synthesis of π-conjugated polymers within the interiors of carbon nanotubes (CNTs). In this process, thiophene-based oligomers are encapsulated within CNTs as precursors and are subsequently polymerized by thermal annealing. This polymerization increases the effective conjugation length of the thiophenes, as confirmed by transmission electron microscopy and absorption peak red shifts. This work also demonstrates that these polythiophenes can serve as effective markers for individual CNTs during Raman imaging with single-wavelength laser excitation due to their strong absorbance. In addition, stable carrier injection into the encapsulated polythiophenes is found to be possible via electrochemical doping. Such doping has the potential to produce π-electron-based one-dimensional conductive wires and highly stable electrochromic devices.

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.