Exploring Through-Space Charge Transfer-Mediated Optoelectrochemical Properties of Dual-State Luminescent Aliphatic Polymers and Optoelectronic Responses toward Metal Ions.

Herein, natural-synthetic hybrid dual-state luminescent conducting polymers (DLCPs/DLCP1-DLCP8) possessing significant optoelectrochemical properties are strategically developed by the polymerization of prop-2-enamide, cis-butenedioic acid, 2-acrylamido-2-methylpropane-1-sulfonic acid, and in situ-generated 2-(3-acrylamidopropanamido)-2-methylpropane-1-sulfonic acid alongside the grafting of gum tragacanth. The spectroscopic data of aliphatic DLCPs affirm DLCP7 as the most stable supramolecular assembly endowing optoelectronic properties. Computational calculations identified -C(═O)NH-, -C(═O)OH, -OH, and -SO3H as subluminophores. The absorption spectra, excitation wavelength-/solvent-polarity-/concentration-dependent luminescence, solid state luminescence, aggregation-induced enhanced luminescence, and time-correlated single photon count (TCSPC) studies confirm the occurrence of aggregation-mediated intramolecular through-space charge transfer (ITSCT) in the excited state of DLCP7. Mulliken charge, natural bond orbital, dipole moments, and electronic potential surface analyses confirm the charge donor-acceptor system in DLCP7. Furthermore, the selective optoelectronic response of DLCP7 toward Ca2+/Cu(II) at 438/574 nm is explored using ultraviolet-visible spectra, TCSPC analyses, a dynamic light scattering study, and computational investigations. The chelation-enhanced luminescence and ITSCT inhibition are responsible for turn-on and turn-off detections of Ca2+ and Cu(II), respectively. Cu(II) → Cu(I) reduction in a DLCP7 solution is inferred from electrochemical and spectroscopic analyses. The conductivities of 9.65 × 10-5 S cm-1 (solid state) and 44.35 × 10-5 S cm-1 (solution) in DLCP7 are validated by current-voltage and electrochemical impedance measurements. Again, strong electronic conductivities of 43.89 × 10-5 S cm-1 (solid state)/53.34 × 10-5 S cm-1 (solution) and 45.42 × 10-5 S cm-1 (solid state)/64.81 × 10-5 S cm-1 (solution) are observed in Ca2+-DLCP7 and Cu(II)-DLCP7, respectively.

Synthesis and optimization of chitosan-incorporated semisynthetic polymer/α-Fe2O3 nanoparticle hybrid polymer to explore optimal efficacy of fluorescence resonance energy transfer/charge transfer for Co(II) and Ni(II) sensing.

Initially, four synthetic fluorescent polymers (SFPs) are synthesized from α-methacrylic acid and methanolacrylamide monomers carrying -C(=O)OH and -C(=O)NH subfluorophores, respectively. Among SFPs, ∼1:1 incorporation of subfluorophores in the optimum SFP3 is explored by spectroscopic analyses. Subsequently, chitosan is incorporated in SFP3 to produce five semi-synthetic fluorescent polymers (SSFPs). The maximum incorporation of chitosan in SSFP4 is supported by different spectroscopies. In SSFP4, strong electrostatic interactions among polar functionalities of chitosan and synthetic polymer favor resonance-associated charge transfer (RCT) from SSFP4-(amide) to SSFP4-(canonical). Finally, three hybrid fluorescent polymers (HFPs) are fabricated encapsulating iron-oxide nanoparticle within SSFP4. The maximum proportion of hematite (α-Fe2O3) phase in HFPs is explored by spectroscopic, magnetometric, microscopic, and light scattering studies. HFP2 shows local/RCT/fluorescence resonance energy transfer (FRET) emission at 393/460/570 nm. In HFP2, FRET, RCT, and ratiometric pH-sensing within 3.0-6.5 phenomena are explored by solvent polarity effects, time-correlated single photon counting, quantum yield measurements, alongside I431/I460 vs pH plots. RCT and FRET emissions of HFP2 are utilized for selective sensing of Co(II)/Ni(II) with limits of detection of 4.990 ppb (460 nm)/4.353 ppb (570 nm) and 45.041 ppb (428 nm)/29.617 ppb (527 nm) in organic and aqueous solutions, respectively.

Synthesis of Intrinsically-Fluorescent Aliphatic Tautomeric Polymers for Proton-Conductivity, Dual-State Emission, and Sensing/Oxidation-Reduction of Metal Ions.

Herein, fluorescent conducting tautomeric polymers (FCTPs) are developed by polymerizing 2-methylprop-2-enoic acid (MPEA), methyl-2-methylpropenoate (MMP), N-(propan-2-yl)prop-2-enamide (PPE), and in situ-anchored 3-(N-(propan-2-yl)prop-2-enamido)-2-methylpropanoic acid (PPEMPA). Among as-synthesized FCTPs, the most promising characteristics in FCTP3 are confirmed by NMR and Fourier transform infrared (FTIR) spectroscopies, luminescence enhancements, and computational studies. In FCTP3, ─C(═O)NH─, -C(═O)N<, ─C(═O)OH, and ─C(═O)OCH3 subluminophores are identified by theoretical calculations and experimental analyses. These subluminophores facilitate redox characteristics, solid state emissions, aggregation-enhanced emissions (AEEs), excited-state intramolecular proton transfer (ESIPT), and conductivities in FCTP3. The ESIPT-associated dual emission/AEEs of FCTP3 are elucidated by time correlated single photon counting (TCSPC) investigation, solvent polarity effects, concentration-dependent emissions, dynamic light scattering (DLS) measurements, field emission scanning electron microscopy images, and computational calculations. The cyclic voltammetry measurements of FCTP3 indicate cumulative redox efficacy of ─C(═O)OH, ─C(═O)NH─/-C(═O)N<, ─C(─O─)═NH+─/─C(─O─)═N+, and ─C(═N)OH functionalities. In FCTP3, ESIPT-associated dual-emission enable in the selective detection of Cr(III)/Cu(II) at λem1/λem2 with the limit of detection of 0.0343/0.079 ppb. The preferential interaction of Cr(III)/Cu(II) with FCTP3 (amide)/FCTP3 (imidol) and oxidation/reduction of Cr(III)/Cu(II) to Cr(VI)/Cu(I) are further supported by NMR-titration; FTIR and X-ray photoelectron spectroscopy analyses; TCSPC/electrochemical/DLS measurement; alongside theoretical calculations. The proton conductivity of FCTP3 is explored by electrochemical impedance spectroscopy and I-V measurements.

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(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.