Nontraditional Redox Active Aliphatic Luminescent Polymer for Ratiometric pH Sensing and Sensing-Removal-Reduction of Cu(II): Strategic Optimization of Composition.

Here, redox active aliphatic luminescent polymers (ALPs) are synthesized via polymerization of N,N-dimethyl-2-propenamide (DMPA) and 2-methyl-2-propenoic acid (MPA). The structures and properties of the optimum ALP3, ALP3-aggregate and Cu(I)-ALP3, ratiometric pH sensing, redox activity, aggregation enhanced emission (AEE), Stokes shift, and oxygen-donor selective coordination-reduction of Cu(II) to Cu(I) are explored via spectroscopic, microscopic, density functional theory-reduced density gradient (DFT-RDG), fluorescence quenching, adsorption isotherm-thermodynamics, and electrochemical methods. The intense blue and green fluorescence of ALP3 emerges at pH = 7.0 and 9.0, respectively, due to alteration of fluorophores from -C(═O)N(CH 3 ) 2 / -C(═O)OH to -C(O - )═N + (CH 3 ) 2 / -C(═O)O - , inferred from binding energies at 401.32 eV (-C(O - )═N + (CH 3 ) 2 ) and 533.08 eV (-C(═O)O - ), significant red shifting in absorption and emission spectra, and peak at 2154 cm -1 . The n-π* communications in ALP3-aggregate, hydrogen bondings within 2.34-2.93 Å (intramolecular) in ALP3 and within 1.66-2.89 Å (intermolecular) in ALP3-aggregate, respectively, contribute significantly in fluorescence, confirmed from NMR titration, ratiometric pH sensing, AEE, excitation dependent emission, and Stokes shift and DFT-RDG analyses. For ALP3, Stokes shift, excellent limit of detection, adsorption capacity, and redox potentials are 13561 cm -1 /1.68 eV, 0.137 ppb, 122.93 mg g -1 , and 0.33/-1.04 V at pH 7.0, respectively.