On-substrate postsynthetic metal ion exchange as a tool for tuning electrochromic properties of materials

The hydrazone-based ligand containing polymerizable styrene groups has been designed and prepared. The radical polymerization reaction carried out on ITO substrate leaded to formation of cross-linked thin film of poly-L, which has been converted into polymeric complexes with iron(II) and copper(II) metal ions using dip-coating method. The uniform distribution of metal ions in the obtained thin films has been confirmed by the energy-dispersive X-ray spectroscopy (EDS) and their electrochromic properties were investigated. The metal-ion exchange reaction was monitored in solution by NMR titration and on-substrate by EDS analysis. It was found that Cu(II) ions can be exchanged on-substrate with Fe(II) ions leading to the change of electrochromic properties of materials. Polymeric complexes have been characterized in terms of their electrochromic properties such as long term stability, switching times and coloration efficiencies. It was found that polymers poly-Fe-L obtained by dip-coating method and metal ion exchange exhibit similar electrochromic properties what prove that the transmetalation reaction can be powerful tool for changing observed colors of the films and tuning the electrochromic properties of materials.