Encapsulating viologen derivatives in anionic MOFs: Photochromism and photocontrolled luminescence.

The tunable luminescent materials based on photochromic reactions have received considerable interest due to its potential applications in switches and optical memory devices. However, constructing such materials with ideal properties remains a challenge. In this context, two rare viologen-based host guest materials, 2[MV]·[Zn 6 (PMA) 4 (H 2 O) 4 ] (1), 2[PBM]·[Zn 2 (PMA) 2 (H 2 O) 6 ] (2), (MV·2NO 3 ​= ​1,1'-dimethyl-(4,4'-bipyridine)-1,1'-diium dinitrate; PBM·2NO 3 ​= ​4,4'-(1,4-phenylene)bis(1-methylpyridin-1-ium) dinitrate; H 2 PMA ​= ​pyromellitic acid), have been prepared by encapsulating viologen derivatives into the anionic metal-organic frameworks produced from pyromellitic acid ligands and zinc cations. Due to the presence of photoactive guest MV2+/PBM2+ and the short O⋯N+ distances between the oxygen atom of carboxylate groups and pyridine ring of guest, both complexes display fast-responsive reversible naked photochromism from colorless to blue or yellow upon UV–Vis irradiation At the same time, these host-guest materials exhibit good fluorescence emission behavior and their fluorescence can be reversible modulation under light irradiation. These are rare examples of fluorescence switching materials based on host-guest system that involve the electron-transfer photochromic process. Two novel MOF-based host-guest compounds were prepared by incorporating the photoactive viologen derivatives into the anionic framework, which exhibit photochromism upon UV–Vis light irradiation and photocontrolled luminescence. [Display omitted] ● Two host-guest complexes are prepared by incorporating the viologen derivatives into the anionic MOFs. ● Complexes 1 and 2 exhibit fast-responsive photochromism upon UV–Vis light irradiation. ● Complexes 1 and 2 show good luminescent emission and reversible luminescence switching. [ABSTRACT FROM AUTHOR]