Synthesis of Metal-Containing Poly(thiophene methines) via Solid- and Melt-State Polymerization and Their Related Applications as Highly Sensitive Ni²⁺ Chemosensors

Abstract

Metal-containing polymers have attracted continuous interest, for they combine the features of a metal complex and a polymer. Here, a series of thiophene methine based phenanthroline ligands (L1−L4) and their metal (Zn(II) and Cd(II)) complexes were prepared as monomers. Accordingly, metal-containing poly(thiophene methines) were prepared from these metal complexes via solid-and melt-state polymerization (S(M)SP). The polymerization process was preliminarily investigated by a crystal structure study, NMR analysis, and absorbance spectra. Furthermore, the metal-free polymer (PL4) prepared directly from the ligand via MSP was tested as a metal ion chemosensor, which showed good selectivity and excellent sensitivity toward Ni 2+ with a detection limit of 4.1 × 10 −9 M.

Synthesis of Conjugated Main-Chain Ferrocene-Containing Polymers through Melt-State Polymerization

“…After reaction at 110 °C for 48 h, unreacted monomer was first removed by hexane and the final product was extracted by Soxhlet extraction with dichloromethane as solvent. The polymerization temperatures of both Fc-containing polymers are lower than those of our previously reported thiophene-methine based metallopolymers but higher than those other metal-free polymers with a thiophene-methine structure …”

“…The possible polymerization pathway of FcT was proposed from the monomer’s crystal structure. As shown in the crystal packing map (Figure c), the shortest intermolecular Hal–Hal (Br1–Br2) distance is 4.412 Å and the shortest C1–C10 distance is 5.314 Å, which are longer than those of our previously reported metal complexes (4.044 Å for Hal–Hal distance and 4.935 Å for C1–C10 distance). However, there is an infinite ···C1–C10–C1–C10··· chain in FcT , which means FcT has an far shorter effective Hal–Hal distance of 4.412 Å (6.602 and 6.827 Å in the reported metal complexes), resulting in a lower onset temperature.…”

“…92% and 95% of Fe remain in PFcT8 and PFcTP8 , respectively. In our recent work toward preparing metallopolymers with pendant coordination fragments by S­(M)­SP, 50–70% of the metal was expelled due to the high reaction temperature . Fortunately, the remaining metal contents of these Fc-containing polymers are higher than those of the previously reported metallopolymers due to the high stability of Fc and low polymerization temperature.…”

“…TPX and TP8X were prepared by our previously reported method . To a mixture of aldehyde (10 mmol) and 2-bromothiophene (40 mmol) dissolved in glacial acetic acid (40 mL) was added a solution of BF 3 (46.7 wt % in Et 2 O, 5 mL).…”

“…However, in terms of structure, this method may lead to an irregular structure and poor experimental reproducibility. On the basis of the above research as well as our recent proposal of preparing a metallopolymer by solid-/melt-state polymerization (S­(M)­SP), we assume that S­(M)­SP would be a good choice to prepare a conjugated Fc-containing polymer. Because its only requirement is treating the monomers at an appropriate temperature to promote the reaction, S­(M)­SP is a solvent-free, catalyst-free, and easy to implement method to prepare polymers.…”