Uniaxially-oriented epitaxial nanowires of H2TPP

The growth of porphyrinic nanostructures of well-defined shapes and sizes has received much interest due to their attractive photophysical, photochemical, and electronic properties. The self-assembly of porphyrin nanostructures in organic solvents and in the solid state is well known, but always relies on the establishment of relatively strong interactions such as hydrogen bonding, metal coordination, and ionic bonding. When only π−π interactions are active, the formation of unwanted irregular aggregates usually occurs. Here, we develop an epitaxial strategy for growing uniaxially-oriented and crystalline nanowires of free-base tetraphenyl porphyrin (H2TPP). The process is based on the growth of the organic adsorbate on a water-soluble single crystalline substrate, properly designed for inducing the anisotropic diffusion of ad-molecules. The so-obtained nanowires are characterized by optical absorption spectroscopy, scanning probe microscopy and transmission electron microscopy, giving a thorough landscape of morphological and structural properties of the assembly. Thanks to the solubility of the substrate, wet-transfer techniques can be applied and the nanowires placed on any other solid substrate maintaining their uniaxial order. Otherwise, they can be dispersed in other liquids in view of more complex processing of the active nanostructures.