Threading the Needle: Fluorescent Poly-pseudo-rotaxanes for Size-Exclusion Sensing
Author(s)Evans, Rachel C.; Belger, Christian; Fox, Niamh Denise Willis; Fennell, John Francis; Swager, Timothy M
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Poly-pseudo-rotaxanes have been formed through the threading of cucurbit[n]urils (CB[n]) onto the cationic electron-poor poly(pyridyl vinylene), PPyV. The threading of CB[n] onto the PPyV backbone is confirmed by a broadening and upfield shift in the PPyV 1H NMR signals. Encapsulation of PPyV within the CB[n] macrocycles produces dramatic fluorescence enhancements with improved solubility. The threading ability of the CB[n] on the PPyV backbone is governed by the dimensions of the particular CB[n] portal, which grows with increasing number of methylene-bridged glycoluril repeat units. CB is too small to thread onto the PPyV backbone. The portal of CB requires extra time, suggesting high preorganization and/or macrocycle deformation are required to thread onto PPyV. Alternatively, the portal of CB appears to be large enough such that it does not have sufficiently large dipole–dipole interactions with the PPyV chain to promote a strong threading equilibrium. However, we find that the portal of CB is optimal for the threading of PPyV. The PPyV-CB[n] system was further exploited to demonstrate a dual-action sensor platform, combining the PL-responsive behavior demonstrated by PPyV toward electron-rich analytes with the size-exclusion properties imparted by volume of the respective CB[n] cavities. Thin films of PPyV-CB were found to display reversible photoluminescence quenching when exposed to vapors of the biologically relevant molecule indole, which is recovered under ambient conditions, suggesting prospects for new size-exclusion based selective sensory schemes for volatile electron-rich analytes.
DepartmentMassachusetts Institute of Technology. Institute for Soldier Nanotechnologies; Massachusetts Institute of Technology. Department of Chemistry
Chemistry of Materials
American Chemical Society (ACS)
Willis-Fox, Niamh et al. “Threading the Needle: Fluorescent Poly- Pseudo -Rotaxanes for Size-Exclusion Sensing.” Chemistry of Materials 28.8 (2016): 2685–2691.
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