Study of the Edge-on Self-Assembly of Axially Substituted Silicon(IV) Phthalocyanine Derivatives in a Template on the HOPG Surface

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.

On-Surface Synthesis of Nonmetal Porphyrins

We report the on-surface synthesis of a nonmetal porphyrin, namely, silicon tetraphenylporphyrin (Si-TPP), by the deposition of atomic silicon onto a free-base TPP layer on a Ag(100) surface under ultrahigh vacuum (UHV) conditions. Scanning tunneling microscopy provides insights into the self-assembly of the TPP molecules before and after Si insertion. Silicon coordinates with all four nitrogen atoms of the TPP macrocycle and interacts with a silver atom of the substrate as confirmed by scanning tunneling spectroscopy, X-ray photoelectron spectroscopy, and complementary density functional theory calculations. The Si-TPP complex presents a saddle-shaped conformation that is stable under STM manipulation. Our study shows how protocols established for the on-surface metalation of tetrapyrroles can be adopted to achieve nonmetal porphyrins. Complementary experiments yielding Si-TPP and Ge-TPP on Ag(111) highlight the applicability to different main group elements and supports. The success of our nonmetal porphyrin synthesis procedure is further corroborated by a temperature-programmed desorption experiment, revealing the desorption of Ge-TPP. This extension of interfacial complex formation beyond metal elements opens promising prospects for new tetrapyrrole architectures with distinct properties and functionalities.

Assemblies of porphyrin and phthalocyanine derivatives studied by STM

Porphyrins and phthalocyanines are currently a prevalent topic with great potential due to their abundant photonic/electronic properties. The study of porphyrin or phthalocyanine supramolecular architectures on solid surfaces is laying the foundation for the further development of molecular electronics or other structures in applications. Above all, the invention of scanning tunneling microscopy (STM) has opened a new path to explore these concepts on surfaces. Self-assemblies on solid surfaces can be probed with STM at submolecular resolutions to disclose the conformations and arrangements of molecules on an individual molecule basis. In this paper, the progress of STM research on porphyrin and phthalocyanine derivatives over past ten years is reviewed. We introduce the self-assembled structures of different porphyrins or phthalocyanines. Throughout the review, the structures, thermodynamics, and dynamics have been emphasized, which are essential current and future research themes.