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

Abstract

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 °C disappearing at 35 °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.