Hierarchical self-organization of perylene bisimide-melamine assemblies tofluorescent mesoscopic superstructures

A series of three perylene tetracarboxylic acid bisimide dyes 3a-c bearing phenoxy substituents at the four bay positions of the perylene core were sy nthesized and their complexation behavior to complementary ditopic dialkyl melamines 8a-c was investigated. Binding constants and Gibbs binding energi es for the hydrogen bonds between the imide and the complementary melamine moiety have been determined in several solvents by NMR and UV/Vis titration experiments with monotopic model compounds 5 and 9. The effects of the sol vent polarity and specific solvent-solute interactions on the degree of pol ymerization of (3.8)(n), are discussed, and a general formula to estimate t he chain length of [AA - BB](n) nylon-type supramolecular polymers is deriv ed. In addition to the formation of a hydrogen-bonded supramolecular chain, pi-pi interactions were observed for perylene bisimide - melamine assembli es 3b.8b and 3b.8c in aliphatic solvents. The orthogonal nature of hydrogen bonding and pi-pi interactions leads to three-dimensional growth yielding large-sized aggregates already in dilute solution. On suitable substrates, densely intertwined networks of nano- to mesoscopic strands are formed whic h have been investigated by electron microscopy, confocal fluorescence micr oscopy and optical polarization microscopy. The high fluorescence and excel lent photostability of these superstructures is promising for future studie s on energy migration and artificial light harvesting at the nano- and meso scopic length scale.