Noncovalent Functiconalization of SWNTs with Azobenzene-Containing Polymers: Solubility, Stability, and Enhancement of Photoresponsive Properties

Azobenzene-derived photoactive polymers (P1-P3) containing pyrene pendants were designed and synthesized (M-w similar to 30 000) for the noncovalent functionalization of single-walled carbon nanotubes (SWNTs). P1-P3 were found to be highly effective for the solubilization of SWNTs in common organic solvents, resulting in hybrid materials with enhanced thermal stability. The solubilization process was mostly driven by the pi-pi a stacking interactions of pyrene with SWNTs. It also brings the azobenzene chromophores to the vicinity of nanotube surface, thereby allowing the electronic interactions between them. In addition to that, stacking of the pyrene and subsequent wrapping of the polymer around CNT surface provides more volume for the photoisomerization of azobenzene. These effects eventually accelerate the kinetics of photoisomerization of azobenzene in the polymer-SWNT composite. The photoalignment property of the composite was also increased when compared to that of the parent polymer which was studied by means of photoinduced birefringence.