Extended-conjugation π-electron systems in carbon nanotubes

Extending pi-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 pi-electron extension, however, can generate products exhibiting chemical instability, poor solubility or disordered structures. Herein, we report a novel strategy for the synthesis of pi-conjugated polymers within the interiors of carbon nanotubes (CNTs). In this process, thiophenebased 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 pi-electron-based one-dimensional conductive wires and highly stable electrochromic devices.