Tailor-made anodically coloring organic-inorganic hybrid electrochromic materials derived from phenothiazine cores

Abstract

Electrochromic materials (ECMs) are crucial for the advancement of electrochromic devices (ECDs). While cathodically coloring ECMs have been extensively studied, their anodically coloring counterparts have received less attention. In this study, we present a novel organic molecule based on inexpensive phenothiazine derivatives, which exhibit promising anodically coloring electrochromic properties. These properties are characterized through combined theoretical calculations and experiments. By introducing two methoxy substituents, the reactive 3,7-positions of the phenothiazine core are protected, enhancing electrochemical stability and introducing new optical properties. Additionally, the molecule is further functionalized with a phosphonic acid anchoring group to create an organic-inorganic hybrid electrochromic film. The resulting film undergoes two successive one-electron redox reactions, transitioning from transparent to greenish-blue and then to blue, with moderate optical contrasts. Notably, the film displays a rapid response time of less than 1 second and an impressive coloration efficiency of approximately 470 cm2/C for the first redox reaction. Furthermore, the film demonstrates exceptional long-term stability, with over 2,000 cycles of reversibility, surpassing any previous findings. These results emphasize the significance of tailor-made design principles for anodically coloring ECMs, which are crucial for the advancement of ECDs and optoelectronic applications..