Electrochromic 2,5-Dihydroxyterephthalic Acid Linker in Metal−Organic Frameworks

Metal–organic frameworks (MOFs) are diverse in color owing to a large variety of molecular structures. Herein, electrochromism of M-MOF-74 (M = Mg, Mn, Co or Zn) is reported, which is a honeycomb nano-framework in which hexagonally packed 1D arrays of metal cations are coordinated with 2,5-dihydroxyterephthalic (dhtp) acid linker. Raman spectroscopy upon electrochemical doping combined with density functional theory calculations reveals redox reactions of the linker while the metal cations stay divalent as probed by X-ray photoemission spectroscopy (XPS). Excellent adhesion of the MOFs to glass allows the synthesis of quality thin films to be implemented into electrochromic devices that exhibit promising color contrast and durability.