Tuning Stopper Size in Multiresponsive [2]Rotaxanes for Fluoride Anion Selective Metastability.

[23]Crown-7-ether incorporated [2]rotaxanes, comprising an anthracene blocker and 4-isopropylphenyl/cyclohexyl end groups, exhibited varying degrees of metastability with a range of chemical (base, halide anions) and physical (solvent, heat) stimuli. Among halides, fluoride, chloride, and bromide anions affected the deslippage of 23-crown-7-ether in 4-isopropylphenyl stoppered [2]rotaxane. Surprisingly, only fluoride anions could selectively induce deslippage in cyclohexyl stoppered [2]rotaxane, whose fluorescence quenching provided an additional tool to selectively detect the fluoride anions down to 2.49 × 10-7 M.