Light emissions of ratiometric aliphatic redox polymer from canonical, anion, and anion-aggregate: Reduction-associated naked eye detections of Hg(II), Fe(III), and Cu(II)

Herein, pH-responsive luminescent polymers (PRLPs) showing the multi-light emissions (MLEs) are strategically synthesized using different mole ratios of 2-methylidenebutanedioic acid and N,N-dimethylprop-2-enamide monomers. Of different PRLPs, the optimum attachment of nontraditional heteroatomic luminophores (NTHLs), i.e., –C(=O)N(CH3)2, –C(–O–)=N+(CH3)2, –C(=O)OH, and –C(=O)O–, in PRLP4 is explored through spectroscopic and thermal analyses, supported by the theoretical calculations. In solutions, the presence of different forms of PRLP4, i.e., PRLP4, PRLP4-canonical, and PRLP4-anion, along with their aggregates is supported by the spectroscopic analyses and theoretical calculations. In different forms of PRLP4, pH-dependent NTHLs; hydrogen bonding, dipolar, and supramolecular interactions; hydrophobic/hydrophilic balance; and through space conjugation facilitate aggregations, electronic transitions, and MLEs. The ratiometric pH sensing within pH = 6.5–8.5 and reduction-associated fluoro-colorimetric sensing performances of PRLP4 are explored through computational calculations; spectroscopic, microscopic, and thermal analyses; and electrochemical measurements. The fluoro-colorimetric sensing of Fe(III), Cu(II), and Hg(II) at pH = 6.5, 7.5, and 8.5 results in limits of detection of 1.226, 0.135, and 0.283 ppb, respectively.