Only during the last decade, first mechanosensitive molecular junctions were investigated and communicated with the scientific society. Destructive quantum interference (QI) was observed by mechanical manipulation of two π-systems on top of each other from simple bi-molecular systems, such as oligo phenylene ethynylenes (OPE`s), over paracyclophane- (PCP) and ferrocene containing single-molecule junctions. Porphyrins, with an aromatic π-system of the size of one nm, are prominent building blocks for molecular electronics. To further study the structure-property relationship of two π-systems under mechanical manipulation, we therefore designed a cyclophane comprising two cofacial porphyrins. The molecule is decorated with one gold-anchoring group per porphyrin sub-unit, pointing into the opposite directions of the macrocycle. Planar xanthene units bridge the macrocycle in the lateral positions of the porphyrins with respect to the anchoring groups. This design ensures rigidity of the macrocyclic structure, acetylenes between the bridge and the porphyrins allow for rotation over the C-C triple bond and thus, mechanical manipulation into the direction of the electrodes. Over a 15 steps synthesis with a fourfold <i>Sonogashira</i> macrocyclization as key step, we isolated and characterized this unique porphyrin-cyclophane with a face-to-face distance of 3.24 Å in the solid-state structure, thus 0.16 Å smaller the van-der-Waals distance. The design, synthesis and well-behaved transport of suitably stable single-molecule junctions (a prerequisite for mechanosensitivity studies) will be presented.

Cofacial porphyrin cyclophanes for mechanosensitive single-molecule junctions

ACS Spring Meeting 2021

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