Unraveling the timescale of the structural photo-response within oriented Metal-Organic Framework films

In nature, many processes are governed by photo-triggered communication that becomes initiated by a photo-active molecule and is responded by a structurally responsive matrix acting as the host structure. However, in synthetic photo-responsive materials, the design of such guest-host systems and, thus, the possibility to induce a remotely and spatially controlled photo-response remains a significant barrier. This attempt becomes even more challenging for solid systems which, consequently, limits the number of synthetic photo-switchable systems in solid-state. Yet, it is the much desired wireless and non-invasive mode of solid photo-switching systems which are much needed for the development of various promising applications especially in the medical and pharmaceutical sector. This work demonstrates a solid-state model film
system based on an azobenzene-infiltrated metal organic framework structure, DMOF-1, which upon irradiation by light undergoes a structural change. The foundation of this thesis is the fabrication of a system that provides a structurally flexible environment within the zinc-based framework which reacts to the isomerization of the azobenzene molecule within its pores. For this, in a first step, by means of a reproducible fabrication technique, the growth and orientation of the DMOF-1 film system was studied by x-ray diffraction (XRD) and grazing incidence wide-angle x-ray scattering (GIWAXS) measurements. By spectroscopic and gravimetric techniques, the azobenzene infiltration within the DMOF-1 pores of the film structure was confirmed. The main findings of the thesis involve the structural dynamics of the crystalline DMOF-1 film system prompted by the azobenzene isomerization process, which so far have not
been assessed in the field of photo-switchable MOF (film) systems. For the first time, an experimental approach is presented to investigate such systems using a laser supported GIWAXS set-up for the elucidation of the changes in the crystalline MOF structure, together with spectroscopic measurements to combine the knowledge of the dynamic processes on a molecular level. The findings reported in this thesis provide further insight how to tune the photo-triggered processes in crystalline MOF films systems. The results reported herein will aid in a deeper understanding of the complex dynamics in crystalline photo-active systems, which are vital for the development of novel light-controlled devices that may eventually be powered simply by sunlight.