X-ray and UV Dual Photochromism, Thermochromism, Electrochromism, and Amine-Selective Chemochromism in an Anderson-like Zn Cluster-Based 7-Fold Interpenetrated Framework.

Smart materials are highly desirable over the recent decade due to the growing demand of complicated nature. Stable stimuli-responsive smart materials exhibit widespread potential for applications in smart windows, sensors, separators, chemical valves, and release platforms but are rare. Despite being good candidates, viologen-based multifunctional smart materials are still a challenging task for chemists. To obtain such materials, the judicious strategy is to introduce polynuclear metal-carboxylate clusters as electron donors into a stable framework to increase chromic sensitivity. Toward this endeavor, we have synthesized a novel viologen-based polymer with a unique Anderson-like metal-carboxylate cluster, [Zn(bpybc)(o-BDC)]·2NO·6HO (bpybc = 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium, o-BDC = -benzenedicarboylic acid) (), which is a particular 7-fold interpenetrated framework with a 3D network in which bpybc ligand as the linker and ZnOC as the second building unit (Zn SBU) were used as 6-connected nodes. More importantly, it shows excellent chromic behavior in response to multiple external stimuli especially soft X-ray and UV dual light, temperature, electricity, and organic amines, which stand out in the viologen-based polymers. Interestingly, the coloration process of from "core" to "edge" is observed upon heating at the appropriate temperature, which has not yet been found in other reported thermochromic materials. Of particular interest for is the couple of quaternary stimuli-sensitive abilities because it simultaneously meets the following conditions: (i) the capability of withstanding high light, higher temperature, extreme pH, and other harsh conditions; and (ii) the high sensitivity to external stimuli keeping away from photodegradation, thermal relaxation, side reactions, and so on. To be noted, has high thermal stability and chemical stability, which are excellent advantages as smart materials. To further develop possible practical utilization, has been doped into the polymer matrixes to construct a hybrid film, which not only keeps the response to external stimuli but also significantly improves the repeatability of the photochromic process, indicating that a new smart device with multi-stimuli-responsive functions will emerge successively in the future.