The lifetime of a charge separated state is enhanced by the effects of solvent polarity and the coordination controlled shuttling of a dumbbell in a porphyrin/fullerene rotaxane.

Single-molecule junctions (SMJs) have been fabricated using layers generated by diazonium electroreduction. This process immobilizes the molecule and creates a direct C-Au covalent bond between the molecule and the electrode. As a result, rigid oligomers of variable length, mainly perpendicular to the surface, are formed. The oligomers are based on porphyrin derivatives in their free base or cobalt complex forms. The conductance of the grafted oligomers has been studied by means of the scanning-tunneling-microscopy break-junction (STM-bj) technique and G(t) measurements, and the lifetime of the single-molecule junctions has been investigated. The conductance histograms indicate that charge transport in the porphyrins is relatively efficient and influenced by the presence of the cobalt center. With both systems, random telegraph G(t) signals are easily recorded showing SMJ on off states. The SMJs then stabilize and exhibit a surprisingly long lifetime around 10 s, and attenuation plots, obtained by both G(t) and STM-bj conductance measurements, give identical attenuation values. This work shows that highly stable SMJs can be prepared using diazonium grafting approach.

Associations of hydrophobic cavities with porphyrin derivatives used to mimic haemoprotein structures are featured in this article and may inspire innovative research in the field of cucurbiturils.