Spin Interactions in Supramolecular Assemblies of Porphyrin Oligomer Radical Anions

Diradicals have potential applications in spintronics, molecular electronics, and dynamic nuclear polarization due to their unique electronic structure. Supramolecular diradicals are particularly attractive, as changes in conformation can be used to switch the spin state. In this work, we explore a class of supramolecular diradicals formed by the self-assembly of charged zinc porphyrin oligomers with bidentate ligands such as 1,4-diazabicyclo[2.2.2]octane (DABCO) and 4,4'-bipyridyl. Field-dependent nutation experiments on the anions of porphyrin ladder complexes show nutation frequencies corresponding to doublet and triplet species, which can both be attributed to the same spin system using simulations based on the time evolution of the density matrix. Density functional theory was used to calculate dipolar coupling tensors and provided insights into the electronic structure of these double-stranded assemblies.