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.