Alternating isomerization of pseudo-rhodamine and its ultrafast electrochromic video display

As an eye-friendly display technology, electrochromic displays still face challenges in playing videos due to their slow response speed. Here, we designed and developed pseudo-rhodamine electrochromic molecules through a "tandem all-in-one" synthetic strategy that covalently integrates three distinct functional units within a single molecule. This molecular architecture simultaneously achieves exceptionally high heterogeneous electron transfer rate constant and ultrahigh molar absorption coefficient. We verified the underlying electrochromic mechanism involving a two-electron redox process of pyridinecarboxylic acid derivative units coupled with reversible pseudo-rhodamine spirocyclization. By implementing this tandem all-in-one molecular engineering strategy, different functional subunits within the electrochromic molecule are mutually bonded to interact through alternating reaction sequences, enabling near-synchronous operation of individual units. The resulting electrochromic display demonstrates ultrafast response speeds (35 milliseconds for bleaching and 65 milliseconds for coloration), capable of smooth video playback and rapid switching between digital states. The design principle showcases a prospective design pathway for the development of ultrafast electrochromic video displays.