Chromo-Fluorogenic Sensing of Fe(III), Cu(II), and Hg(II) Using a Redox-Mediated Macromolecular Ratiometric Sensor

The design and synthesis of pH-responsive nonconventional multi-light emitting macromolecules suitable toward high-performance pH-sensitive reduction-associated chromo-fluorogenic sensing are very challenging and not reported to date. Herein, pH- and excitation-dependent redox active multi-light emitting macromolecular ratiometric sensors ( MRS s) are synthesized through the polymerization of prop-2-enenitrile and N, N -dimethylamino acrolein in water medium. Of different MRS s, the optimum photophysical and reduction-associated chromo-fluorogenic sensing capabilities of MRS3 are explored through spectroscopic, thermal, photoluminescence, computational, microscopic, and electrochemical measurements alongside videographic representations of reduction associated rapid color changes from yellowish brown Fe(III) to pale green Fe(II), blue Cu(II) to green Cu(I) followed by brown Cu(0), and colorless Hg(II) to yellow Hg(I) at pH = 7.0, 8.0, and 9.0, respectively. The emissions of MRS3, MRS3 -canonical, and MRS3 -aggregate at 434, 465, and 572 nm, respectively, are facilitated by the −C(═O)N(CH 3 ) 2 /–C(−O – )= N + (CH 3 ) 2 and −C≡N heteroatomic luminophore-assisted inter- and intra-molecular nonconventional and conventional hydrogen bonds, n→ π * transitions, dipolar interactions, N -branching associated rigidity, and hydrophobic interaction. The alteration of −C(═O)N(CH 3 ) 2 to −C(−O – )═N + (CH 3 ) 2 and significant decrease in bond order of −C≡N are explored through spectroscopic, computational, and photophysical studies. MRS3, MRS3 -canonical, and ( MRS3 -canonical)-aggregate are utilized toward reduction-associated chromo-fluorogenic sensing of Fe(III), Cu(II), and Hg(II) with very low limits of detection of 0.486, 0.276, and 0.016 ppb at pH = 7.0, 8.0, and 9.0, respectively.