Nanomolecular Arrays of Porphyrins and Fullereno-Porphyrins

Molecule-based nano-objects with the capacity to perform the functions of optoelectronic components are of considerable current interest. Suitably structured compounds have been used as models for photoreaction centers or as molecular electronic components that may be assembled into prototypical memory and logic architectures. Thermal stability and reversible behavior in (photonic or electric) "read-write" cycles are required for such use. The ubiquitous porphyrins and the recently discovered fullerenes are robust compounds (in a chemical sense) with extended conjugated pi-systems, which appear to have the basic build-up, as required in this respect. In this project we present the design of novel nanometer-sized fullereno-porphyrin arrays and propose a general strategy for their efficient synthesis. The proposal is based an the use of a specifically tetrafunctionalized porphyrin as "synthon" (i.e. a core molecular unit with proper reactivity) for the purpose of building-up with the help of [4+2]-cycloadditions regularly structured, nanometer-sized oligo-porphyrinoid arrays, suitable for their subsequent modification in covalent multi-fullerenoadducts. At first, the synthesic strategy thus involves the preparation of suitable porphyrinoid building blocks with the effective complementaty reactivities (of "dienophiles" and of conjugated "dienes") as required for the [4+2]-cycloaddition. The covalent assembly of a variety of specific well structured, one- and two-dimensional multiporphyrin arrays, to be arranged in electronically conjugated (linear) "ladders", in "stars" and in "super-rings" thus will be examined. These covalent multi-porphyrin assemblies are robust scaffolds, to be used subsequently for the covalent attachment of a regular and record number of C60- fullerene units and resulting in nanometer-sized fullereno-porphyrin arrays. The fullereno-porphyrin arrays, obtained in this way, are predicted to be nanometer-sized molecular objects with an unparalleled capacity for the reversible uptake of electrons, i.e. to be reversibly functioning reservoirs of a large number of electrons. They are likely to also have the capacity for absorption of long wave-length light. Structural, spectroscopic, electroanalytical and photophysical investigations are thus planned to study the expected unusual structural and electronic properties of these compounds, which will render themselves particularly suitable for the electrochemical detection of single molecules. Due to their (in part predictable) remarkable properties an a molecular level, the nanometer-sized fullereno-porphyrin arrays will be of particular interest as a new and practical entry to the field of nanomolecular optoelectronic components.