Revealing the photo-triggered structural dynamics of photo-responsive MOFs grown on oriented ceramic thin films

Description

At present, most developments based on microelectronics, sensing and optical devices rely on the technology of thin-film fabrication. Recently, numerous functional Metal-Organic Frameworks (MOFs) thin films have been exploited and applied in these fields. This is mainly due to the versatile chemical nature of MOFs that allows to modulate their physical properties as well. These include selective engineering of the MOF porosity, but also to implement susceptibilities to external stimuli such as light to realize a photo-responsive system. One of the most straightforward strategies to modulate the MOF structure by light is to infiltrate MOF pores with photo-responsive chromophores of suitable size (e.g. azobenzene).
Herein, we pursue oriented ceramic thin films based on copper hydroxide nanobelts converted to Cu2bdc2, [1] which serves as the supporting MOF for the subsequently grown flexible zinc-based DMOF-1.[2] The infiltration of DMOF-1 by azobenzene was confirmed by ATR and Raman spectroscopy. Our research aims to elucidate the photo-triggered structural dynamics in this class of materials induced by the reversible photo-isomerization of azobenzene between its trans (ground state) and cis structure (excited state). Hence, the photo-response of the infiltrated azobenzene inside the MOF pores forces the flexible framework structure to adapt to the trans/cis isomerization of the chromophore. At the picosecond-pump probe station at the Austrian SAXS beamline at Elettra synchrotron radiation source we successfully pumped the infiltrated thin films by UV light (342 nm) and induced the forward switching of the flexible crystalline thin film, whilst the recovery of the system was achieved by illumination with blue light. The thereby provoked structural transitions of the crystalline film induced by the photo-switchable chromophore were pursued by time-resolved Grazing-Incidence Small Angle X-Ray Scattering (GISAXS) measurements. Thus, we demonstrate the very first photo-switch in oriented MOF thin films accompanied by structural changes of the host system. Further, pursuing our concept proposed herein allows us to reversibly switch the MOF system in centimeter-scale on-demand, which makes the system highly attractive for the development of smart materials in e.g. optoelectronic applications. These results will allow us to gain further knowledge on the underlying structural transitions with the ultimate goal to understand and characterize the photo-induced dynamics in crystalline solids.

[1] (a) Falcaro, P.; Okada, K.; Hara, T.; Ikigaki, K.; Tokudome, Y.; Thornton, A. W.; Hill, A. J.; Williams, T.; Doonan, C.; Takahashi, M.; Falcaro, P. Nature materials 2017, 16, 342.
[2] Yanai, N.; Uemura, T.; Inoue, M.; Matsuda, R.; Fukushima, T.; Tsujimoto, M.; Isoda, S.; Kitagawa, S.; J. Am. Chem. Soc. 2012, 134 (10), 4501–4504.

Period	26 May 2021
Event title	2nd International Conference on Light and Light-based Technologies: ICLLT 2021
Event type	Conference
Location	Online/Gazi, TurkeyShow on map
Degree of Recognition	International