Dynamic optical and thermal modulation of electrochromic smart windows and sunglasses based on benzothiadiazole-extended viologen derivatives

Smart windows can regulate indoor lighting and heat intensity by isolating external light and heat, thereby achieving the goal of saving building energy consumption. However, traditional smart windows require additional power consumption to adjust color changes and thus regulate transmittance, and can only achieve relatively single control of light intensity and heat. Developing smart windows with dynamic photothermal modulation remains challenging. This paper reports two novel benzothiadiazole extended viologen derivatives DBTBB and DBTBH. The carboxymethylcellulose sodium hydrogel-state electrochromic devices based on DBTBB and DBTBH showed good electrochromic performance including a low operating voltage, a rapid response time, a high optical contrast, excellent cycling stability, and a large coloration efficiency. A dynamic photothermal modulation electrochromic smart window self-powered by a small commercial solar panel was constructed using the electrochromic hydrogel based on DBTBB, which could sense the changes in external irradiating light intensity and dynamically adjust the indoor light and heat without additional consumption of electricity, and the adjusting capability increased with the increase of irradiating light intensity. In addition, the application in smart color changing sunglasses self-powered by a solar panel was also investigated, the electrochromic sunglasses showed dynamic transmittance modulation in response to irradiating light intensities with good cycling stability, a gradual change in purple color from light to dark was observed as the irradiating light intensity increased from 105  →  225→415  →  650→920 lux. Moreover, both text and a colored logo were clearly displayed under different irradiating light intensities. This provides new methods for electrochromic applications in commercial settings and improving human quality of life, thereby creating new possibilities in the increasingly intelligent world.