One of the goals of ARO-MAT is to synthesize edge-fused porphyrin nanobelts, which are expected to exhibit strong global ring currents. This objective has not yet been achieved, but substantial progress led to three publications: “Bending a photonic wire into a ring” (Nat. Chem. 2022, 14, 1436–1442), “Covalent template-directed synthesis of a spoked 18-porphyrin nanoring” (Angew. Chem. Int. Ed. 2023, 62, e202302114) and “b,b-Directly linked porphyrin rings: Synthesis, photophysical properties and fullerene binding” (J. Am. Chem. Soc. 2023, doi: 10.1021/jacs.3c03549). Work is in progress towards using related structures to access porphyrin nanobelts.
Another goal of ARO-MAT is to investigate porphyrin nanoribbons with multiple paramagnetic metal centers, as an approach to spintronic materials. Substantial progress has been made in this area. We investigated poly-lanthanide nanoribbons and this work was published in “Singly and triply linked magnetic porphyrin lanthanide arrays” (J. Am. Chem. Soc. 2022, 144, 8693–8706). Low temperature SQUID magnetometry measurements reveal intramolecular antiferromagnetic exchange coupling between GdIII centers and the phase memory times are long enough to test quantum computational schemes using microwave pulses.
During the second reporting period (01/04/2022 to 30/09/2023), we made substantial advances in understanding the electronic and magnetic properties of porphyrin-based nanoribbons (Work Packages 1 and 5), leading to several high-profile publications. This includes investigation of anthracene-porphyrin nanoribbons (Angew. Chem. Int. Ed. 2023, 62, e202307035), demonstrating phase-coherent charge transport through a porphyrin nanoribbon-graphene junctions (J. Am. Chem. Soc. 2023, 145, 15265–15274) and exploring the enhanced coherence generated by coupling spins through a delocalized π-system in vanadyl porphyrin oligomers (Chem 2023, DOI: 10.1016/j.chempr.2023.09.013). We also demonstrated key steps towards the synthesis of edge-fused porphyrin nanobelts. We also devised a synthetic route to porphyrin nanorings with para-phenylene bridges (Org. Lett. 2023, 25, 378–383). Our theoretical work on understanding aromaticity in large π-conjugated macrocycles generated two publications (Angew. Chem. Int. Ed. 2022, 61, e202201231 and Chem. Sci. 2023, 14, 1762–1768), and has contributed towards a change in the way the community thinks about molecular nanostructures. We are also comparing the electronic structure of large porphyrin-based nanorings with smaller analogous rings constructed purely from carbon atoms, i.e. cyclo[N]carbons. As part of this work, we reported the first structural characterisation of a doubly anti-aromatic cyclocarbon, C16 (Nature 2023, DOI: 10.1038/s41586-023-06566-8) and we published a strategy for creating cyclocarbons that are stabilised by catenane formation (Nat. Chem. 2023, DOI: 10.1038/s41557-023-01374-z). Another strand of this work has been the investigation of polaron delocalisation on linear and cyclic molecular wires using EPR spectroscopy. We made substantial progress in this area during this reporting period and several publications on these results are in preparation.
