Synthesis of Semisynthetic Dual-State Fluorescent Polymers and Roles of Starch/Pectin on AIET-Assisted Dual-Emission, Conductivity, and Metal-Ion Sensing

Abstract

The strategic and systematic synthesis of aggregation-induced energy transfer (AIET)-active dual-state emitting semisynthetic polymeric materials having promising conductivity and suitability in heavy and transition metal ion (HTMI) sensing is indeed a challenging task especially involving purely aliphatic moieties. In this work, initially, synthetic aliphatic macromolecular luminogens (AMLs) are synthesized and optimized through nuclear magnetic resonance (NMR)/Fourier transform infrared (FTIR) spectroscopy and thermogravimetric (TG) analyses based on the optimized incorporation of atypical heteroatomic fluorophores (AHFs), i.e., −CONH−, −CON<, and −COOH, of constituent isopropylacrylamide, methylpropanoic acid, methylidenebutanedioic acid comonomers, and in situ anchored tertiary amidic 3-(N-isopropylmethacrylamido)-2-methylpropanoic acid. The efficacy of supramolecular interaction-driven emission in optimized AML4 is further augmented by the encapsulation of starch and pectin in semisynthetic starch-grafted-AML (SAML) and pectin-grafted-AML (PAML) through the enrichment of AHFs. Among SAMLs/PAMLs, the optimization of AHFs and natural polymers (starch/pectin) through various spectroscopic techniques and I/I 0 measurements emerges excellent dual-state (solid and solution) emissions and conductivity in SAML3/PAML4. The AIET-assisted dual-light emissions are envisaged by absorption spectra, time-correlated single photon count (TCSPC) studies, and bandgap calculations of SAML3-/PAML4-aggregate and SAML3/PAML4. The AIETprompted emission in SAML3-/PAML4-aggregate is further attested through concentration-dependent emission and aggregationenhanced emission studies, solvent polarity effects, quantum yield calculations, and scanning electron microscopy photomicrographs. The grafting-associated conductivity increment in SAML3/PAML4 is substantiated by I−V and impedance spectroscopy. The dualemission phenomena in SAML3/PAML4 enable rapid, selective, and sensitive detections (in ppb levels) of Cu(II)/Cr(III) and Hg(II)/Fe(III) at different wavelengths by SAML3/SAML3-aggregate and PAML4/PAML4-aggregate, respectively. The strong coordination of the HTMIs with AHFs of SAML3/PAML4 and SAML3-/PAML4-aggregate are confirmed by absorption, emission, NMR, FTIR, and X-ray photoelectron spectroscopies; TG analyses; dynamic light scattering measurements; and TCSPC studies.