Colorimetric Sensing of Chirality Based on Synergistic Effect of Multiple Chiral Amide Receptors Consecutively Organized along Poly(phenylacetylene) Backbone

Despite the increasing demand for simple, rapid, and convenient chirality-sensing methods, the development of reliable and practical colorimetric sensors for chirality assays remains challenging. In this study, we investigated the applicability of poly(phenylacetylene) with chiral amide receptors derived from l-phenylalanine (PPAPhe) to such chiral sensors. The various advantages of PPAPhe as a chiral sensor, including its immediate colorimetric response upon the addition of chiral amino acids and the large chirality-selective color difference between the d- and l-enantiomers, validate its potential as a colorimetric probe for both qualitative and quantitative analyses of chirality. To elucidate the excellent enantioselective color-differentiating ability of PPAPhe, its colorimetric response was compared with that of several model compounds: the monomer containing a single chiral receptor, statistical copolymers with almost randomly distributed chiral receptor units, and block copolymers bearing a segment composed of consecutive receptor units. A detailed examination revealed that a contiguous sequence of multiple chiral receptor units is indispensable for the chirality-selective colorimetric response of PPAPhe. In addition, the findings of this study further indicate the possibility that the organization of multiple receptor units along a polymer backbone could impart highly enhanced and improved chiral recognition ability, even though the receptor itself possesses insufficient and minute chiral recognition ability. As an example of further applications, PPAPhe was verified to be capable of colorimetric chiral sensing of chiral drugs.