Magnetic response of porphyrin-based hierarchical molecular superstructures

We propose a novel approach for the bottom-up nanofabrication of complex molecular superstructures, characterized by regular arrays of magnetically active molecules. The system is formed by alternating layers of metal tetraphenyl porphyrins (MTPP) and ditopic ligand molecules (DPNDI), achieved through the consecutive sublimation of the molecules from crucibles in a vacuum environment. Molecular ordering is ensured by initiating the process with a regular 2D MTPP wetting layer and leveraging the high directionality of coordination bonds between the porphyrin metal ion and the ligand anchoring groups. The magnetic response is provided by the localized magnetic moments of the porphyrin metal ions.
We have already demonstrated the feasibility of this approach using oxygen-passivated iron as a substrate, where (i) a complex molecular superstructure consisting of 2D+n layers, with n=3, was successfully fabricated, and (ii) a strong magnetic interaction between the substrate and a CoTPP wetting layer was observed, even at room temperature. However, (i) the modifications in the electronic and magnetic configuration of CoTPP molecules upon coordination with ligands, and (ii) the magnetic interaction with the substrate when these molecules are embedded within the superstructure, remain to be addressed—particularly when the CoTPP layer is not in direct contact with the substrate.
These challenges require the sensitivity and resolution provided by a synchrotron source, coupled with advanced instrumentation for magnetic studies of ultra-thin molecular layers, such as the one available at the BOREAS beamline.