Multistimuli-Responsive Materials Based on Zn(II)-Viologen Coordination Polymers and Their Applications in Inkless Print and Anticounterfeiting.

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.