Chiral Poly(ionic liquid) with Nonconjugated Backbone as a Fluorescent Enantioselective Sensor for Phenylalaninol and Tryptophan

Here, a novel fluorescent chiral poly(ionic liquid) (S)-PCIL-4 with nonconjugated backbone is designed and synthesized in the control of micelle through free-radical polymerization, whose fluorescence emission maximum is at λem,max = 430 nm. It is observed that polymers with spatially proximate units (phenyl group and pyridinium cation) have photoluminescence through spatial π–π and ion−π interaction. Then, (S)-PCIL-4 can be served as a fluorescent turn off/on sensor for chiral recognition of phenylalaninol and tryptophan in the presence of Cu(II). For example, when (S)-PCIL-4–Cu(II) is treated with (R/S)-phenylalaninol, it will exhibit different fluorescence responses. Values of the enantiomeric fluorescence difference ratio for phenylalaninol and tryptophan are 1.10 and 1.08, respectively. In brief, we believe that the approach opens up a possible pathway to prepare a variety of fluorescent polymers with nonconjugated backbone and proves to be desirable in further application.