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

Abstract

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.