Excited-State Intramolecular Proton- and Inter-Polymer Charge-Transfer of Semiconducting Redox Polymers for Fe(III), Cd(II), and Hg(II) Sensing
Mousumi Deb, Shrestha Roy, Madhushree Mitra, Joy Sankar Deb Roy, Deepak Chowdhury, Narendra Nath Ghosh, Dilip K. Maiti, Mincheol Chang, Mostafizur Rahaman, Pijush Kanti Chattopadhyay, Nayan Ranjan Singha
Abstract
Herein, IPCT-ESIPT exhibiting nonconventional fluorescent semiconducting polymers ( FSP s) are synthesized using poly(vinyl alcohol) (PVA), 2-acrylamido-2-methylpropanesulfonic acid, N -hydroxymethyl acrylamide, and in situ-generated 2-(3-( N -(hydroxymethyl)acrylamido)propanamido)-2-methylpropane-1-sulfonic acid. The IPCT- and ESIPT-mediated triple-light emission at different excitation wavelengths (λ ex ); coexistence of FSP6 -amide, FSP6 -imidol, and FSP6 -amide canonical; and ICT-/PET-assisted sensing capabilities of FSP6 are explored via spectroscopic analyses, computational calculations, electrochemical measurements, and impedance analyses. The π – π * transitions, IPCT–ESIPT, N -branching- and −CH 3 group (side chain)-associated rigidity, alongside hydrophilic/hydrophobic balance are facilitated by −C(═O)NH/–C(═O)N, −C(═N)OH, −C(O – )N +, and −SO 3 H heteroatomic subluminophores. The enhancement in hydrogen bonds and stabilization of −C(O – )N + /–C(═N)OH in a polar-protic environment by the hydroxyl functionalities of semicrystalline PVA facilitate IPCT/ESIPT emission and electron/proton transport through the channels generated in the polymer matrix. The ICT-mediated reduction and oxidation of Fe(III) and Cd(II), respectively, and PET-mediated reduction of Hg(II) are explored via quenching/enhancement of photoluminescence in the presence of Fe(III) and Hg(II)/Cd(II), spectroscopic analyses, cyclic voltammetry, and impedance data. The detections of Fe(III), Cd(II), and Hg(II) by FSP6 -amide, FSP6 -amide canonical, and FSP6 -imidol, respectively, are confirmed by low limits of detection of 1.225 (λ ex1 ), 5.241 (λ ex2 ), and 2.249 (λ ex3 ) ppb. The ac impedance spectroscopy and I – V data of semiconducting FSP6 indicate proton/electron conductivity = 3.37 × 10 –5 /2.80 × 10 –5 S cm –1 (pH = 7.0/8.0).