Hybrid Electrochromic Multilayer Films Based on Fe(II)-Metalloviologens and TiO2 Nanoparticles

Metallosupramolecular coordination polyelectrolyte, Fe(II)-metalloviologen(FEN), was prepared by the reaction of Fe(II) with a novel bisterpyridine ligand. As active components, FENs could be assembled into electrochromic multilayer films with negative charged polystyrene sulfate(PSS) by the sequential deposition layer-by-layer technique. Numerous analytical instruments, such as UV-Vis spectroscopy, atomic force microscopy(AFM), tunneling electron microscopy(TEM), zeta-potential measurement and electrochemical measurement have been utilized to characterize their morphology, optical and electrochromic properties. It has been observed that as-prepared films exhibited multi-colour changes by triggering with different potentials. However, the low optical contrast of multilayer films would limit their further applications. In order to overcome this problem, semiconductor TiO₂ nanoparticles(TiO₂) were incorporated into FEN multilayers by layer-by-layer approach. By carefully optimizing the film structure, as-resulted hybrid films containing FEN, TiO₂ and PSS exhibited high optical contrast, suitable response time and long-term stability. Such hybrid films should be promising candidates to meet the requirements for deve- loping flexible displays and electrochromic devices.