Metal‐Organic Frameworks as Hosts for Fluorinated Azobenzenes: A Path towards Quantitative Photoswitching with Visible Light

Fifteen new photochromic hybrid materials were synthesized by gas phase loading of fluorinated azobenzenes, namely ortho ‐tetrafluoroazobenzene ( tF ‐AZB), 4 H ,4 H ′‐octafluoroazobenzene ( oF ‐AZB), and perfluoroazobenzene ( pF ‐AZB), into the pores of the well‐known metal‐organic frameworks MOF‐5, MIL‐53(Al), MIL‐53(Ga), MIL‐68(Ga), and MIL‐68(In). Their composition was analysed by elemental (CHNS) and DSC/TGA. For pF ‐AZB 0.34 @MIL‐53(Al), a structural model based on high‐resolution synchrotron powder diffraction data was developed and the host‐guest and guest‐guest interactions were elucidated from this model. These interactions of O−H⋅⋅⋅F and π⋅⋅⋅π type were confirmed by significant shifts of the O−H frequencies in loaded and unloaded MOFs of the MIL‐53 and MIL‐68 series. Most remarkably, all of the synthesized F ‐AZB@MOF systems can be switched with visible light, and some of them show almost quantitative (>95 %) photo‐isomerization between its E and Z forms with no significant fatigue after repeated switching cycles.