Immobilization of redox-driven spin state switches

• Applicants: Professorin Dr. Vera Krewald; Professor Dr. Biprajit Sarkar; Professor Dr. Joris van Slageren
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation ; Physical Chemistry of Solids and Surfaces, Material Characterisation ; Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560717977

Developing and controlling spin state switches from the molecular level is a fundamental challenge with direct importance for emerging fields such as molecular spintronics. Central questions concern the development of suitable molecular complexes with reliable trigger and read-out options and their immobilisation on surfaces as a first step towards device fabrication. Thorough insights from high-level spectroscopic and theoretical investigations are essential to understand the electronic structures in the different switch positions as well as the switching and read-out processes. This project focuses on redox switches with optical readout, specifically homo- and hetero-dinuclear iron and cobalt complexes with redox-active imino-quinonoid bridges, as well as their immobilisation. Upon redox triggering, the unpaired electrons on the metal ions and the bridge will be strongly antiferromagnetically coupled, leading to a large spin state change. Additionally, these complexes are expected to display spin crossover, electron transfer induced spin state switching, and mixed-valency coupled with spin-state changes. Optical readout will be facilitated by incorporating pyrene groups at the bridging unit in conjunction with magnetic circular dichroism measurements. Click chemistry will be used for surface immobilization of the complexes modified with appropriate anchoring groups. All systems will be thoroughly characterised using spectroscopy (UV-vis, NIR, IR, rR, EPR, MCD, Mössbauer), electrochemistry and spectroelectrochemistry. Quantum chemical studies will focus on electronic structure characterisation and analysis by quantification of Marcus–Hush theory for mixed-valent systems with an existing ab initio approach, which will be expanded to three-center systems. Mutually beneficial collaborations with synthesis, spectroscopy and theory groups will be established for further characterisaton of the systems. We expect that our project will deliver fundamental insights and first steps towards applications for using redox processes as simple and benign switches to drive large spin state changes in surface-immobilised molecular complexes with optical read-out.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2491: Interactive Spin-State Switching