Solvophobic versus Electrostatic Interactions Drive Spontaneous Adsorption of Porphyrins onto Inorganic Surfaces: A Full Noncovalent Approach

The successful transferring of a porphyrin complex assembly from a solution to a solid surface is important for an economical development of functional materials, biomaterials, and sensing devices. The understanding of the mechanisms and factors that drive spontaneous and stable deposition, in water, of porphyrins (and their complex species) onto inorganic surfaces paves the way for a straightforward and environmentally friendly noncovalent functionalization of solid surfaces. Here, we show that surface charge considerations need to be carefully considered if water-soluble porphyrin derivatives have to be successfully immobilized onto zinc oxide (ZnO) layers deposited on glass. In particular, it will be demonstrated that the electrostatics of the glass support has a central role in driving the layering of charged (anionic and cationic) porphyrin derivatives. Finally, our results underline the robustness and versatility of the noncovalently driven deposition-in terms of both reproducibility and stability of the porphyrin assemblies-and shed light on the crucial role played by dispersion interactions, which (in our experimental conditions) prevent the more specific covalent interactions.