Multifunctional anthraquinone-full-substituted linear polyphosphazene for fluorescence sensing, electrochromic, and energy storage applications

In this study, a fully substituted functional polyphosphazene (PPZ) was successfully synthesized by grafting 2-hydroxyanthraquinone (2-HAQ) onto a linear PPZ backbone. The as-synthesized polymer integrates the electroactive and fluorescent properties of anthraquinone (AQ) units with the flexible inorganic–organic hybrid structure of PPZ, making it a promising multifunctional polymer in TNP detection, electrochromism and energy storage applications. Electrochromic (EC) measurements demonstrate that the polymer film exhibits reversible EC redox behavior in 0.5 M LiClO₄/THF electrolyte with a transparent to yellow-black color transition. Compared with small-molecule 2-HAQ, the polymer shows superior film-forming capability and enhanced film stability, and the assembled sandwich-type EC device retains reversible color-switching performance during cycling. Furthermore, the synthesized polymer possessed remarkable fluorescence behavior, and the practical application in 2,4,6-trinitrophenol (TNP) detection was realized, which exhibited a low detection limit (L_OD) of 75 nM. When used as a polymer cathode for aqueous zinc-ion batteries (ZIBs), the polymer significantly improved battery performance, featuring high specific capacity and ultra-stable long-term cycling behavior. Overall, these findings clearly demonstrate the versatility and great application potential of PPZ-HAQ, and also open up new possibilities for the further application of multifunctional PPZ systems.