Pentiptycene Polymer/Single-Walled Carbon Nanotube Complexes: Applications in Benzene, Toluene, and o-Xylene Detection

We report the dispersion of single-walled carbon nanotubes (SWCNTs) using pentiptycene polymers and their use in chemiresistance-based and QCM-D sensors. Poly(p-phenylene ethynylene)s (PPEs) incorporating pentiptycene moieties present a concave surface that promotes pi-pi interactions and van der Waals interactions with SWCNTs. In contrast to more common polymer-dispersing mechanisms that involve the wrapping of polymers around the SWCNTs, we conclude that the H-shape of pentiptycene groups and the linear rigid-rod structure creates a slot for nanotube binding. UV-vis-NIR, Raman, and fluorescence spectra and TEM images of polymer/SWCNTs support this dispersion model, which shows size selectivity to SWCNTs with diameters of 0.8-0.9 nm. Steric bulk on the channels is problematic, and tert-butylated pentiptycenes do not form stable dispersions with SWCNTs. This result, along with the diameter preference, supports the model in which the SWCNTs are bound to the concave clefts of the pentiptycenes. The binding model suggests that the polymer/SWCNTs complex creates galleries, and we have demonstrated the binding of benzene, toluene, and o-xylene (BTX) vapors as the basis for a robust, sensitive, and selective sensing platform for BTX detection. The utility of our sensors is demonstrated by the detection of benzene at the OSHA short-term exposure limit of 5 ppm in air.