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(CH3)2/ –C(═O)OH to –C(O−)═N+(CH3)2/ –C(═O)O−, inferred from binding energies at 401.32 eV (–C(O−)═N+(CH3)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.

The design and synthesis of pH-responsive nonconventional multi-light emitting macromolecules suitable toward high-performance pHsensitive 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 (MRSs) are synthesized through the polymerization of prop-2-enenitrile and N,Ndimethylamino acrolein in water medium. Of different MRSs, 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, MRS3canonical, 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.

Here, four nontraditional fluorescent polymers (NTFPs) of varying N,N-dimethyl-2-propenamide (DMPA) and butyl prop-2-enoate (BPE) mole ratios, i.e., 2:1 (NTFP1), 4:1 (NTFP2), 8:1 (NTFP3), and 16:1 (NTFP4), are prepared via random polymerization in water. The maximum fluorescence enhancement of NTFP3 makes it suitable for ratiometric pH sensing, Cu(II) sensing, and pH-dependent cell imaging of Madin-Darby canine kidney (MDCK) cells. The oxygen donor functionalities of NTFP3 involved in binding and sensing with Cu(II) ions are studied by absorption, emission, electron paramagnetic resonance, Fourier transform infrared (FTIR), and O1s/ Cu2p X-ray photoelectron spectroscopies (XPS). The spectral responses of the ratiometric pH sensor within 1.5−11.5 confirm 22 and 44 nm red shifts in absorption and ratiometric emission, respectively. The striking color changes from blue (436 nm) to green (480 nm) via an increase in pH are thought to be the stabilization of the charged canonical form of tertiary amide, i.e., −C(O − ) N + (CH 3 ) 2 , realized from the changes in the absorption/fluorescence spectra and XPS/FTIR analyses. The through-space n−π* interactions in the NTFP3 aggregate, N-branching-associated rigidity, and nonconventional intramolecular hydrogen bondings of adjacent NTFP3 moieties in the NTFP3 aggregate contribute to aggregation-enhanced emissions (AEEs). Here, structures of NTFP3, NTFP3 aggregate, and Cu(II)-NTFP3; absorption; n−π* interactions; hydrogen bondings; AEEs; and binding with Cu(II) are ascertained by density functional theory, time-dependent density functional theory, and reduced density gradient calculations. The excellent limits of detection and Stern−Volmer constants of NTFP3 are 2.24 nM/0.14234 ppb and 4.26 × 10 3 M −1 at pH = 6.5 and 0.95 nM/0.06037 ppb and 4.90 × 10 3 M −1 at pH = 8.0, respectively. Additionally, the Stokes shift and binding energy of NTFP3 are 13,636 cm −1 /1.69 eV and −4.64 eV, respectively. The pH-dependent MDCK cell imaging ability of noncytotoxic NTFP3 is supported via fluorescence imaging and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.