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Recently, stimuli-responsive materials have attracted great attention, while most of them respond to single or two stimuli. Thus, it is essential to design multifunctional stimuli-responsive materials and develop their applications. The strategy that constructing high-dimensional coordination polymers facilitates the application scope of a viologen-based photochromic system is put forward and confirmed for the first time. Herein, a novel multistimuli-responsive viologen-based Zn-MOF with a two-dimensional framework has been successfully designed and synthesized. Complex 1 exhibits chromic behavior under a variety of external stimuli such as 365 nm UV, X-rays, heat, electricity, and ethylamine. More interestingly, the crystal state of complex 1 displays dual fluorescence and room-temperature phosphorescence (RTP) emission and emits a yellow afterglow when turning off the UV lamp. In addition, Eu­(III)-functionalized hybrids, Eu 3+ @Zn-MOF, were prepared by coordinated postsynthetic modification based on viologen complexes for the first time. The sample of Eu 3+ @Zn-MOF inherits the photochromic characteristics of the viologen complexes and gives the distinctive fluorescence of the europium ions. Based on the multicolor switching of 1 and Eu 3+ @Zn-MOF, their possible practical utilization was successfully developed in the fields of inkless, erasable print media, electrochromic information tag printing, information encryption, and anticounterfeiting.

Here, we report the in situ electrochemical conversion of NiCr2O4 on Ni foam prepared using a hydrothermal strategy to give ultra-thin wrinkled NiOOH-NiCr2O4 amorphous-crystalline nanosheets on Ni foam (NiOOH-NiCr2O4/NF) via anode oxidation in 1.0 M KOH. Owing to the coordination of NiCr2O4 and NiOOH, NiOOH-NiCr2O4/NF shows superior catalytic activity toward the oxygen evolution reaction (OER) with the demand of overpotential as low as 271 mV to drive a geometrical current density of 20 mA cm-2 under alkaline conditions. Notably, it also displays strong long-term electrochemical durability for at least 30 h.

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