A viologen-derived host-guest MOF material: Photochromism, photoswitchable luminescence, and inkless and erasable printing

The encapsulation of photoactive guests into a metal-organic framework is advantageous in endowing extra functionalities such as photochromism and photoswitchable luminescence. In this paper, a host-guest MOF material, [Zn-3(IPA)(4) MV] (1) (H(2)IPA = isophthalic acid, MV center dot 2NO(3) = 1,1'-dimethyl-(4,4'-bipyridine)-1,1'-diium dinitrate) has been constructed by encapsulating simplest methyl viologen guest into the anionic MOF framework. This material exhibits reversible naked-eye detectable photochromic properties varying from colorless to blue upon UV-Vis light irradiation. The MV2+ and the short O center dot center dot center dot N distance between the oxygen atom and pyridine ring of MV2+ play a crucial role in the photochromism of this compound. This host-guest MOF compound shows photoswitchable luminescent properties in the solid state. More interestingly, this host-guest MOF material can be deposited on filter paper and can be employed as inkless print material by controlling the UV-Vis light irradiation with the stencil.