A facile method for colorimetric determination of the enantiomeric purity of amino acids using poly(phenylacetylene) possessing (S)-mandelamide receptors

The development of reliable, practical colorimetric chirality sensors is essential for achieving simple, rapid, and accessible chirality analysis. Conjugated polymers are recognized as a leading platform for such chiral sensors, yet only a few examples demonstrate easily discernible color differences. To overcome this limitation, we investigated the potential of poly(phenylacetylene) bearing chiral (S)-mandelamide receptors (poly-1) as a colorimetric chirality sensor. Poly-1 exhibited an instantaneous colorimetric response dependent on the chirality of the added amino acid derivative, demonstrating its applicability to qualitative chirality analysis. The large chirality-dependent color difference, greater than 110 nm, is easily discernible even with the naked eye. This superior enantiospecific colorimetric response of poly-1 enabled visual estimation of the approximate optical purity of the analyzed guests, which could be precisely quantified using calibration curves. When compared with a previously reported polymer-based chiral sensor (poly-2), poly-1 provided important insights into the molecular design of poly(phenylacetylene)-based chiral sensors. Notably, poly-1's response was highly temperature-sensitive, with its enantioselective colorimetric response observed at 20 degrees C disappearing at 35 degrees C, possibly owing to the simplified design around its chiral amide receptor. The study provides valuable insights for designing future chiral sensors, potentially advancing sensing technologies in diverse fields.