New Generation of Hybrid Materials Based on Hierarchical Assembly of Porphyrin on Supramolecular Scaffolds or Nanostructures

Porphyrins multifunctional properties make these macrocycles intringuing building blocks to build up complex supramolecular assemblies via covalent or non-covalent approaches, either in solution or on inorganic surfaces. In the perspective of development of hybrids organic-inorganic materials, mastering of non-covalent strategies to transfer water soluble porphyrin based assemblies on nanostructured surfaces paves the way to a cost effective and environmentally friendly research that combine the unique properties of nanomaterials with the synthetic versatility of organic chemistry. Noteworthy, the control of spontaneous self-assembly is not trivial, as it is a hierarchically driven process that can proceed through thermodynamic or kinetic pathways. However, in water, complex porphyrin based supramolecular assemblies having a pre-determined and controlled  stechiometry, chirality and composition have been successfully synthetized. Transfer of these assemblies (i.e. chiral porphyrin chiral aggregates, porphyrin-calixarenes, porphyrin-DNA) on inorganic surfaces opens the way to development of new generation of chiral surfaces and sensors, where porphyrins played an important role as spectroscopic probes, capable to overcome sensitivity limitations. Chirality induction and memory is, accordingly, another important requirement that need to be kept during this migration from solution to the solid state. The robustness of non-covalent approaches to achieve a straightforward, controllable and environmentally friendly functionalization of inorganic nanostructures strongly hinges on the competition between retention at the solid state rather than in solution and depends on several factors. Among them, polyelectrolytes secondary structure strongly influences the outcome of spontaneous deposition of porphyrin assemblies on solid surfaces often overriding the mere system electrostatics.