P4: Exposing Luminescent Transition Metal Complexes to Isotropic and Anisotropic Strain by Encapsulation in Stimuli-Responsive MOF Matrices

• Applicant: Professor Dr. Sebastian Henke
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation ; Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 535200000

The project investigates the response of luminescent transition metal complexes (LTMCs) to mechanical strain when encapsulated in stimuli-responsive metal-organic framework (MOF) matrices. It aims to clarify how isotropic (uniform) and anisotropic (directional) strain affects the photophysical properties of LTMCs with Cr(III), Cu(I), and Pd(II)/Pt(II) centres, such as emission wavelength, quantum efficiency, and lifetimes. LTMCs, which are sensitive to environmental factors, show altered luminescence under external pressures – a feature that could enable the design of materials for pressure-sensitive, photonic, or sensing applications. While isotropic strain effects on LTMCs have been explored using diamond anvil cells, anisotropic strain, common in processing techniques like grinding and pressing, is more difficult to recreate and analyse in laboratory setups. MOFs, known for their tunable structures and mechanical diversity, provide a unique platform to study LTMCs under these conditions. These porous, crystalline materials allow for the selection of specific frameworks that exhibit distinct reactions to applied hydrostatic pressure. Cubic MOFs typically compress isotropically, while tetragonal or orthorhombic MOFs often display anisotropic deformation. By embedding LTMCs in MOFs with varying symmetries, this project offers a modular way to explore how LTMC photophysical behaviour changes in response to both types of strain. Embedding LTMCs in tailored MOF matrices not only allows controlled application of mechanical strain but also captures luminescent behaviors challenging to observe in pure LTMCs in solid or solution states. Selected LTMCs will be embedded in MOFs matched by pore size through either crystallization around the LTMCs or post-synthetic encapsulation. The derived LTMC@MOF composites are subsequently examined with high-pressure X-ray diffraction and luminescence spectroscopy to assess structural responses to pressure, including changes in pore size, geometry, and strain distribution on the LTMCs, as well as to understand how the pressure-dependent confinement within the MOFs influences LTMC luminescence. This includes observing shifts in emission wavelength, quantum efficiency, and lifetimes, with a particular focus on chiral LTMCs where dissymmetry may offer additional insight into strain effects. Structural data from X-ray diffraction, combined with luminescence results, will help correlate MOF structural changes with LTMC photophysical properties. Expanding the understanding of how mechanical forces affect LTMC behavior in confined environments, this project aims to inform the design of advanced materials with applications in pressure-sensitive or photonic technologies.

• DFG Programme: Research Units
• Subproject of: FOR 5781: Stimulus-responsive luminescent coordination compounds - STIL-COCOs