Ferrocenyl-Containing Fe(II)-Bipyridinedicarboxamide Polysiloxane Complexes With Multiredox Activity

Abstract

Ferrocenyl-containing Fe(II)-bipyridinedicarboxamide polysiloxane complexes with two redox metal centers were obtained by anionic ring-opening polymerization, polycondensation, and complexation reactions utilizing various Fe^II:Bipy molar ratios of 1:(3–12). The polymer ligand was characterized by liquid-state NMR, FTIR, and gel permeation chromatography (M _n  = 8800). The structure of the polymer-metal complexes (PMCs), that is, the presence of ferrocenyl groups and [Fe^II(Bipy)₃] coordination cross-links with Fe^II–N_Bipy bond formation, was confirmed by solid-state NMR, FTIR, UV–vis, and EDX. The PMCs exhibit multiredox activity showing three redox waves at E _1/2  ≈ −1.3, 0.2, and 1.0 V related to Fc/Fc⁺ couple, [Fe(Bipy)₂]⁺/[Fe^II(Bipy)₃]²⁺, and [Fe(Bipy)₃]²⁺/[Fe(Bipy)₃]³⁺ transformations. The PMCs possess electrochromic properties resulting from the reduction–oxidation of ferrocenyl (Fc/Fc⁺) and [Fe^II(Bipy)₃] fragments and leading to changes in intensity of bands at 628, 542, and 380 nm in the UV–vis spectra (coloring efficiency reaches 13.4 cm²·C⁻¹). The PMCs are flexible, stretchable, and mechanically strong silicone materials with elongation at break, tensile strength, and Young's modulus reaching 110%, 3.5 MPa, and 21.8 MPa, respectively, with self-healing ability at 100°C. The described properties expand applications of PMCs as multiredox materials in polymer engineering for fabrication of (opto)electronic devices and protective coatings with a long service life compared to previously reported multiredox polymers.