Organic/inorganic electrochromic nanocomposites with various interfacial interactions: A review

Electrochromic properties of organic or inorganic materials can be improved through preparing organic/inorganic electrochromic nanocomposites. In electrochromic nanocomposites, the interfacial interactions between the organic and inorganic phases play three important roles in preparation and application of the nanocomposites. Firstly, the interfacial interactions result in stable molecular structures. Secondly, they also improve the electron conduction and ion transport process in the nanocomposites. Thirdly, they enhance the electrochemical and electrochromic properties of the nanocomposites. In this paper, we review the common interfacial interactions including covalent bond, coordination bond, electrostatic interaction, hydrogen bond and pi-pi stacking interaction between the organic and inorganic phases in the electrochromic nanocomposites. The preparation method, the relationship between the structure and properties, and the mechanism of modulation of electrochromic effect in the nanocomposites with various interfacial interactions are surveyed. The strong interfacial interaction, e.g., covalent bond, is helpful for obtaining electrochromic nanocomposites with high electron conduction and high structural strength. However it is very complicated to construct covalent bond between the organic and inorganic phases. Another strong interfacial interaction, the coordination bond is mainly confined to preparation of electrochromic complex of metal ion and pyridine derivative. While, the weak interfacial interactions, e.g., electrostatic interaction, hydrogen bond and pi-pi stacking interaction, exist widely between the organic and inorganic phases in the electrochromic nanocomposites. Relative to single strong interaction, the multiple weak interactions may be a development direction for achieving high performance electrochromic effect in the organic/inorganic nanocomposites, owing to their integrated effect and various adjusting mechanisms of electrochromic properties. (C) 2017 Elsevier B.V. All rights reserved.