Efficiently regulating the electrochromic behavior of naphthalene-diimide-based zirconium-organic frameworks through linker installation

Redox-active metal-organic frameworks (MOFs) have already demonstrated their unique advantages in the field of electrochromism over the past decade. However, controlling and modulating the electrochromic behaviors in specific MOFs remains a significant challenge, as most of the cases reported so far are achieved by designing and constructing new MOFs. Herein, we design a redox-active Zr-MOF with coordination unsaturated pockets, termed NKM-908, based on a naphthalene diimide containing tetratopic carboxylate ligand. The fabricated NKM-908 thin film exhibits a reversible electrochromic behavior, showing a color change from basically colorless to light yellow and then to green. Remarkably, two forms of distinct and precise modulations to the electrochromic performance of NKM-908 are achieved through installations of linear auxiliary bitopic carboxylate linkers (TPDC-X) into the coordination unsaturated pockets, i.e. deepening the color and deriving new colors/shifting modes. This work is a successful attempt in tailoring the color change of electrochromic MOFs as required without synthesizing them from scratch. Considering the high efficiency and conveniency of this post-synthetic modification, such strategy opens up a versatile route in designing electrochromic materials, as well as facilely extending their potential towards practical applications.