Solvent-Dependent Self-Assemblies and Pyridine Modulation of a Porphyrin Molecule at Liquid/Solid Interfaces

On the highly oriented pyrolytic graphite (HOPG) surface, a new porphyrin molecule MT-4 containing a porphine core with six alkyl chains and two carboxyl groups has been explored using scanning tunneling microscopy (STM) technology. Solvent and pyridine regulation have been proved to be two effective ways to control and tune the supramolecular structure of MT-4 at interfaces. Different high-resolution STM (HR-STM) images with highly ordered and closely packed arrangements were gained at the corresponding liquid-solid interface, including phenyl octane (PO), 1-heptanoic acid (HA), and 1-hexanol. Except for the solvent effect, introducing pyridine derivatives such as 4,4'-vinylenedipyridine (DPE) and 4,4'-((1E,1'E)-(2,5-bis(octyloxy)-1,4-phenylene) bis(ethene-2,1-diyl)) dipyridine (PEBP-C8) is also effective to modulate the self-assembly of MT-4. With careful analysis of the STM pictures and the density functional theory (DFT) computational exploration, we figured out the molecular model, interaction energies, and self-assembly mechanism of each system at the interface. This work provides a simple and effective approach for quickly building diverse nanoarchitectures by utilizing different noncovalent interactions. Meanwhile, it would give a perspective to regulate and control self-assembly arrays for devising novel molecular-based materials through more optimal strategies.