Introducing a photo-switchable azo-functionality inside Cr-MIL-101-NH2 by covalent post-synthetic modification.

For the first time an azo functionality was covalently introduced into a MOF by post-synthetic modification. The reaction of Cr-MIL-101-NH(2) with p-phenylazobenzoylchloride (1) and 4-(phenylazo)phenylisocyanate (2) as the reactants led to the compounds Cr-MIL-101_amide and Cr-MIL-101_urea, with the azo groups protruding into the mesoporous cages. XRPD and N(2) sorption measurements confirm the intactness of the framework and the successful covalent modification was proven by IR- and NMR-spectroscopy.

The first porous MOF with photoswitchable linker molecules.

We synthesized a porous twofold interpenetrated MOF [Zn(2)(NDC)(2)(1)] (coined CAU-5) using 3-azo-phenyl-4,4'-bipyridine (1), 2,6-naphthalenedicarboxylic acid, and Zn(NO(3))(2)·6H(2)O. The azo-functionality protrudes into the pores, and can be switched, by irradiation with UV light (365 nm), from the thermodynamically stable trans-isomer to the cis-isomer. Back-switching was achieved thermally and with an irradiation wavelength of λ(max) = 440 nm.