Abstract
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.
Highlights
Because they represent cylindrical nanospaces with high thermal and chemical stability, the interiors of carbon nanotubes (CNTs) have been considered as potentially useful platforms for the fabrication of one-dimensional (1D) nanomaterials by molecular coalescence
The π-conjugated polymers shown in Fig. 1 were synthesized by self-assembly in the interiors of CNTs via vapor-phase encapsulation of thiophene-based oligomers, including α-quaterthiophene (4 T) and α-sexithiophene (6 T), which were subsequently polymerized by thermal treatment
In comparison to an empty nanotube, a linear contrast is observed in the CNT interiors following the encapsulation process for tubes with diameters in the range of 1.0 to 1.7 nm
Summary
Encapsulation was performed by placing the CNTs inside an H-shaped Pyrex glass tube, followed by degassing via heating with a burner under vacuum for 5 to 10 min. Methanol was added to the dispersed DOC solution and the solution was subsequently dropped onto a copper grid coated with a thin carbon film. The substrate was dipped into an ionic liquid (N,N,N-trimethyl-N-propylammonium-bis(trifluoromethanesulfonyl) imide, TMPA-TFSI)
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