Construction of Dimension-Dependent Naphthalenediimide-Based MOF Materials with Free Hydroxyl Active Sites: Stimulation Responses of Ionochromism, Electrochromism, and Visual Artificial Film Labeled on Cations

Smart metal-organic framework (MOF) chromic materials that respond to chemical or electrical stimuli are highly desirable for daily life and optoelectronic applications. Three novel MOFs: [Mn(H₂NDISA)(DMF)₂] (1), [Zn(H₂NDISA)(DMF)₂] (2), and [Cd(H₂NDISA)(DMF)₂] (3) are first synthesized and characterized, based on a H₄NDISA ligand (H₄NDISA (N,N'-bis(3-carboxy-4-hydroxyphenyl)-1,4,5,8-naphthalenetetradicarboximide)) with free hydroxyl active sites. Structural analysis reveals that complexes 1-3 display a 3D supramolecular network, a 2D layered structure, and a 1D chain structure, respectively, because of different intermolecular interactions, affording them with dimension-dependent multistimulus-responsive chromism behaviors. Alkali metal ion-induced chromism is related to topological structures of the complexes, as well as the type and concentration of ions. Regarding alkaline earth metal ions, complexes 1-3 change from yellow to red in Be²⁺. As for fourth-period transition-metal ions, complexes 1-3 display deep red and brown colors in Fe³⁺ and Cu²⁺, respectively, rendering these complexes as selective and sensitive visual ion detectors when fabricated as portable polyvinylidene difluoride-polyethylene glycol@1-3 films (PVDF-PEG@1-3 films). Furthermore, complexes 1-3 exhibit electrochromic switching properties, and chromic voltages are related to dimension of MOFs, which may provide proof-of-concept for low-energy electrochromic applications. This study might enrich the potential application of naphthalenediimide-based MOF materials in cation detection and optoelectronic devices.