Photochromic Metal-Organic Frameworks Based on Host-Guest Strategy and Different Viologen Derivatives for Organic Amines Sensing and Information Anticounterfeiting.

The encapsulation of viologen derivatives in metal-organic frameworks (MOFs) to construct host-guest materials has been widely discussed owing to their distinctive spatial arrangement and physical/chemical properties. Herein, three new photochromic MOFs (NWM-1-3) have been successfully synthesized by 1,1,2,2-Tetra(4-carboxylphenyl)ethylene (HTCPE) ligand as well as three different viologen derivatives based on host-guest strategy. Remarkably, NWM-1-3 exhibit a notable reversible photochromism change from yellow to green under 365 nm UV irradiation. The distance between the electron-deficient N atom in the viologens and the electron-rich carboxylate oxygens satisfies the electron transfer (ET) pathway, and thus ET occurs upon irradiation, producing intermolecular viologen radicals. NWM-1 is able to produce colored responses to different volatile amines by ET and can be recognizable to the naked eye. Differential pulse voltammetry (DPV) analysis and comparative experiments have demonstrated that the host-guest strategy significantly enhances the electron-accepting ability of viologens, thereby achieving superior amine sensing performance. NWM-2 and 3 have been realized in various applications, such as security code, fingerprint, and QR codes for anticounterfeiting. This work provides new host-guest strategy for designing highly sensitive photochromic materials and color-tunable luminescent materials, advancing the development of assembled photochromic materials closer to commercialization.