2D bimolecular self-assembled porphyrin-fullerene nanostructures

Abstract

The formation of self-assembled monolayers of porphyrin molecules and their usefulness as surface supported templates for hosting fullerene molecules has been investigated by means of a room temperature Scanning Tunneling Microscope (STM). In particular, examples of unprecedented addressable supramolecular architectures composed of fullerenes and porphyrins were obtained. Furthermore, the first 2-dimemensional porphyrin based supramolecular host network with porous structure has been self-assembled on a solid surface. This network features a specific chemical sensitivity for different fullerene guest molecules. Various porphyrin derivatives were deposited onto diverse metal substrates. While some combinations did not result in ordered monolayers, many others revealed to form self-assembled structures. Two varieties of porphyrin molecules were examined. On the one hand, single porphyrin cores featuring different functional side-groups were investigated. On the other hand, unique triply-fused diporphyrin cores, also featuring relevant functional groups, have been researched. In addition to several close-packed monolayers, a nanoporous assembly of porphyrin molecules was discovered. This porous network features cavities with a pore-size approximately identical to the size of C60 fullerenes and a pore-pore distance of 3.3 nm. Fullerene molecules were adsorbed onto preformed porphyrin assemblies. Several of these monolayers exhibit interesting fullerene hosting capabilities. The fullerenes have been found to form lines, pairs or adsorb into the pores depending on the underlying porphyrin structure. In particular, the adsorption and dynamics of C60 and C70 fullerenes hosted in the self-assembled nanoporous network on the Ag(111) surface have been studied. Time-resolved STM studies of these supramolecular systems have revealed host-guest interactions resulting in a distinctly dissimilar mobility of the two fullerenes within the porous porphyrin network. Long-range coverage-dependent interactions have been discovered to influence the hopping rates of the adsorbed fullerene guests. These are likely mediated by a complex mechanism involving both the Ag substrate and the flexible porphyrin host network. At increased fullerene coverage this unprecedented interplay results in the formation of large fullerene chains and islands. By applying a lattice gas model with nearest-neighbor interactions and by evaluating the fullerene pair distribution functions the respective coveragedependent guest-guest interaction energies have been estimated.