Multiporphyrin Arrays Assembled Through Hydrogen Bonding

Although relatively weak in isolation, composite H-bonds can be used as an advantage for the assembly of relatively robust and well-defined arrays of molecular components. Porphyrins, with their inherent symmetry, synthetic accessibility and functionality offer ideal base units for the assembly of multicomponent systems by the reversible yet strong intermolecular forces of H-bonding. The geometric precision and strong directionality of H-bonds between relatively rigid donor and acceptor groups can be incorporated into the architecture of porphyrin supramolecular arrays to produce some remarkably complex high-definition assemblies through simple mixing of the component parts. Nevertheless, the very reversibility which allows for ease of construction becomes problematic in ensuring integrity of structure in solution; temperature, solvent and concentration become increasingly important. Measurement techniques are limited to those which can discriminate between the various possible combinations of the component parts to produce discrete oligomeric or polymeric entities. In many cases the measured properties of the assemblies underlying the reason for their construction in the first place also corroborate their structural integrity. Although H-bonding has been used to construct heterotopic porphyrinic arrays comprising porphyrins integrated with other molecular entities, this review is constrained to those systems which principally result in multiporphyrin arrays, although often templated by non-porphyrinic component parts.