Water‐Soluble Poly(quinoxaline‐2,3‐diyl)s Bearing Amino Groups for Chiroptical Sensing of Organic Acids in Water

Achiral poly(quinoxaline-2,3-diyl)s bearing achiral amino side chains, i.e., aminoethoxymethyl (in P1) and aminopropoxymethyl (in P2), are synthesized for their use as chiroptical chemosensors for chiral organic acids in water. These polymers show induced circular dichroism (ICD) in accordance with the induction of asymmetric helical chirality in the aqueous solution of chiral organic acids, including carboxylic acids, hydroxy acids, camphorsulfonic acid, or nucleotides. A higher polymerization degree results in more effective induction of helical chirality due to the accumulation of a higher energy gap (ΔG) between the right- and left-handed helical conformation in one chain of the polymer. This property of helical polymers allows the sensing of chiral acids at low concentrations (down to 1 µm) or low enantiomeric excesses (down to 1% ee).