Multiple stimulus responsive of a novel naphthalenediimide-based 2D alkaline-earth metal MOF material: Hydrochromism, amine-/acid-induced chromism and ionochromism as well as visual artificial film application

Metal–organic frameworks (MOFs) with naphthalene-1,4,5,8-tetracarboxylic dianhydride (H4NDISA) chromophoric unit provide an intriguing platform for the design of multiple stimulus responsive materials. Herein, the first NDISA-based 2D MOF [Ca(H2NDISA)(DMF)3]∙H2O (Ca-NDISA) constructed from alkaline-earth metal ion was successfully synthesized. The structural analysis shown that a binuclear secondary building unit (SBU) [Ca2(COO)2(DMF)6] is extended to generate a 2D planar network structure with abundant open-activity sites, endowing Ca-NDISA with multiple stimulus responsive chromic behaviors. Ca-NDISA could undergo a color change from yellow to red in hydrochromism, rendering it with the applications in detecting the water content of organic solvents, as a humidity sensor when fabricating a PMMA@Ca-NDISA film, and a potential hydrochromic imaging material. In amine-/acid-induced chromism, Ca-NDISA respectively changed its color to red and brown when exposed to strong acid and some small size ammonia/organic amines vapors environment, which makes the PMMA@Ca-NDISA film as a visual and portable recognition detector for acids and amines. In ionochromism, Ca-NDISA is suitable for the naked-eye discrimination and detection of I− with obvious color change to black brown. Our work not only provide a facile way to obtain NDISA-based 2D MOF with multi-stimulus responsive chromic properties, but also present some convenient chromism devices, which will enrich the family of multifunctional chromic materials for practical applications.