Yellow-to-brown and yellow-to-green electrochromic devices based on complexes of transition metal ions with triphenylamine-based ligand

Transmissive-to-colored electrochromism has been obtained by combination of MLCT band from transition metal complex with the electrochromic properties of ligand molecule. The color transitions were from yellow to dark brown for Fe(II) complex, yellow to orange to bluish-green for Co(II) complex and yellow to green for Zn(II) complex. By using metal ion-ligand coordination approach, self-assembly of hydrazone-based ligand containing triphenylamine group with appropriate metal salts (FeCl2, Co(ClO4)2 and Zn(BF4)2) produced novel complexes of general formula [ML2]X2. The isolated complexes were characterized by spectroscopic methods, and Co(II) complex also by X-ray diffraction analysis. The thin films of complexes have been obtained by spray-coating method and they were used in the construction of electrochromic devices, which showed good electrochromic stability, high color contrast of 47.5% for Fe(II), 37.2% for Co(II) and 33.7% for Zn(II) complexes and fast coloring and bleaching times.