Structure-Function Correlation in Switchable DTE@MOF Hybrids: Tracking Local Dynamics and Fatigue Pathways.

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Understanding photoswitchable molecules in porous materials is crucial for advanced optical applications.
• The high mobility of guest molecules within metal-organic frameworks (MOFs) complicates the study of their optical properties and photochromic behavior.
• Dye-MOF interactions significantly influence photochromic response and fatigue resistance.

Purpose of the Study:

• To investigate the light-induced isomerization of a dithienylethene chromophore within the UiO-67 metal-organic framework.
• To elucidate the impact of structural rearrangements and host-guest interactions on photochromic properties and fatigue resistance.
• To provide an atomic-level understanding of the stabilization of different chromophore conformers within the MOF.

Main Methods:

• Solid-state Nuclear Magnetic Resonance (ssNMR) spectroscopy to characterize guest molecule embedment and physical state.
• X-ray diffraction experiments to analyze structural changes in the MOF and guest molecule.
• Diffuse reflectance spectroscopy to monitor photochromic response and fatigue.
• Molecular Dynamics (MD) simulations at the semiempirical quantum chemical level to understand host-guest interactions.

Main Results:

• Solid-state NMR and X-ray diffraction confirmed the embedment and physical state of the photoswitchable dye within UiO-67.
• Diffuse reflectance spectroscopy indicated slight fatigue due to nanoconfinement effects within the MOF pores.
• The open, photoinactive form of the chromophore preferentially occupies MOF side pores, leading to photoswitching fatigue.
• MD simulations revealed specific host-guest interactions and the stabilization of the compact photoinactive conformer.

Conclusions:

• The study provides a comprehensive understanding of photoswitchable molecule behavior within MOFs, combining experimental and computational approaches.
• Nanoconfinement effects and specific pore occupation by different chromophore forms are key factors affecting photochromic performance and fatigue in MOFs.
• This research offers insights into designing robust photoresponsive materials based on MOF-dye systems.