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

Abstract

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.

Excited-State Energy Transfer-Associated Dual Emission of Light-Emitting Polymers Containing Sulfonated Graphene Oxide for Sensing of pH, Co(II), and Bi(III)

“…17,19,36−38 Indeed, in aggregates of LEPs, n → π* interactions involving −C(� O)OCH 2 − and −C(�O)OH/−C(�O)O − functional groups were expected to be responsible for the emission phenomena. 17,19,37,38 Both conventional and nonconventional hydrogen bonds alongside dipolar interactions among −C(�O)OCH 2 −, −N(CH 3 ) 2 , and −C(�O)OH/−C(�O)O − should facilitate aggregation associated n → π* interactions. 17,19,36−39 In addition, the enrichment of oxygen atom donor pockets attached with −C(�O)OCH 2 − and −C(�O)OH/−C(� O)O − functionalities should result in the coordination of metal ions.…”

“…14,15 In nanoparticle incorporated hybrid polymeric materials, enrichment of heteroatomic subfluorophores, such as −C(�O)-OCH 2 −, −N(CH 3 ) 2 , −C(�O)OH/−C(�O)O − , and −SO 3 H/−SO 3 − , contributing high electron density, hydrogen bonding and dipolar interactions, π−π stacking, hydrophilic− hydrophobic balance, and branching associated rigidity is essential to promote aggregation-associated emissions. 13,16,17 Both n → π* and π → π* transitions in aggregate and encapsulation of aliphatic polymer in between the layers of GO may block π−π stacking in SGO, restrict rotation of fluorophores, and favor aggregation-enhanced dual-light emissions. 18 In this work, purely aliphatic light-emitting polymers (LEPs) have been strategically designed using dimethylaminoethyl methacrylate (DMAEMA) and maleic acid (MA) to synthesize electron-rich aliphatic polymeric sensors having −C(�O)-OCH 2 −, −N(CH 3 ) 2 , and −C(�O)OH/−C(�O)O − functionalities.…”

“…Therefore, proper monitoring of pH is important from the industrial, agricultural, environmental, and biological perspectives. 13,17 Among the pH-sensitive fluorescent sensors, ratiometric pH sensors are advantageous for precise pH monitoring because of the self-calibrating ability, sensitivity, and selectivity. 17 Here, the strategic design of dual-light emitting HLEPs with pH-sensitive heteroatomic subfluorophores, i.e., −N(CH 3 ) 2 , −C(�O)OH/ −C(�O)O − , and −SO 3 H/−SO 3 − , may provide high pH sensitivity.…”

“…The differences in the extent of n → π* and π → π* transitions, hydrogen bonding and dipole−dipole interactions, and HOMO−LUMO energy gap are expected to be associated with the protonation and deprotonation of HLEPs. 17,35 Such conversion may result in the different emission wavelengths with pH variation, broadening the opportunity of ratiometric dynamic pH sensing ability of HLEPs. 17 − fluorophores have been developed from the preoptimized composition of purely aliphatic LEPs for dual sensing of Co(II) and Bi(III) at different wavelengths.…”

“…17,35 Such conversion may result in the different emission wavelengths with pH variation, broadening the opportunity of ratiometric dynamic pH sensing ability of HLEPs. 17 − fluorophores have been developed from the preoptimized composition of purely aliphatic LEPs for dual sensing of Co(II) and Bi(III) at different wavelengths. The ESET and aggregation-assisted dual-light emissions, supramolecular interactions, oxygen-rich donor pockets, and pHsensitive functionalities are expected to result in dual metal ion and ratiometric dynamic sensing abilities of HLEPs.…”