Photoresponsive materials enable dynamic remote control
of their
fundamental properties. The incorporation of photochromic molecules
in nanoporous metal–organic frameworks (MOFs) provides a unique
opportunity to tailor the material properties, including the interaction
between the MOF host and guest molecules in the pores. Here, a MOF
film of type HKUST-1 with embedded hexaarylbiimidazole (HABI),
undergoing reversible light-induced reactions between the stable dimer
state and the metastable radical state, is presented. The switching
between the dimer and radical form is shown by infrared, UV–vis,
and electron paramagnetic resonance (EPR) spectroscopy. By transient
uptake experiments with ethanol and methanol as probe molecules, we
show that the dimer-radical switching impacts the host–guest
interaction and, in particular, modifies the uptake amount and diffusion
coefficient of the guest molecules. For ethanol, the diffusion slows
down by 75%. This research presents the first MOF material with photoswitchable
(meta)stable dimer and radical molecules, and it contributes to the
advancement of photoresponsive nanoporous materials.