Alkynyl Linkers as a Design Tool to Gain Control over the Self-Assembly of Meso-Substituted Porphyrins on HOPG

Abstract

Self-assembled monolayers (SAMs) fall generally into two broad categories: those that are covalently bound either to the surface or to each other and those that rely on weaker forces such as hydrogen bonding or van der Waals forces. The engineering of the structure of SAMs formed from weaker forces is an exciting and complex field that often utilizes long alkane substituents bound to core moieties. The core provides the unique optical, electronic, or catalytic property desired, while the interdigitation of the alkane chains provides the means for creating well-regulated patterns of cores on the substrate. This design technique sometimes fails because some of the alkane substituents remain extended into solution rather than become interdigitated on the substrate. One contributor to this is steric hindrance between elements of the core and of the alkane chain. It is shown that the use of an alkyne linker between the core and the alkane chain can, in the case of meso-substituted porphyrins, significantly reduce this steric barrier and allow more stable and predictable surface structures to form. In particular, 5,15-bis­(1-octynyl)­porphyrin and 5,15-bis­(1-tetradecynyl)­porphyrin are shown to form significantly more stable SAMs than their alkane-linked counterparts. Scanning tunneling microscopy is used to provide detailed surface structures. Temperature and solution concentration dependence of the surface coverage is also reported. Density functional theory (DFT) is used to determine the energetic effects associated with alkane substitution at both the meso and β positions and the beneficial energetic effects of the alkyne linker.

On-Surface Self-Assembled Structural Transformation Induced by Schiff Base Reaction and Hydrogen bonds

“…11−13 The structural self-assemblies of a great many functional organic molecules were researched with scanning tunneling microscopy (STM), 14−16 which is a powerful characterization technique with ultrahigh spatial resolution for investigating the molecular self-assemblies at monatomic level in the past few years. 17,18 The controlled modulations of the self-assemblies with other organic molecules, 19,20 and the host−guest molecular architectures with controlled cavities, 21−23 have also been widely studied, especially the networks developed by the hydrogen bonds. 9,24 It is necessary to note the balance is not immutable, and a series of elements will influence the self-assembled nanostructures, for instance, molecular concentration, light irradiation, temperature, solvent polarity, and so on.…”

“…Bottom-up supramolecular self-assembly is regarded as an effective way to construct two-dimensional (2D) nanostructures with controlled properties on the interface and has been extensively applied in catalysis, molecular photonics, sensors, and other fields. − In most cases, the on-surface large-scale architectures are formed via noncovalent molecular forces, for instance, hydrogen bond (H-bond), van der Waals forces, halogen bonds, metal ligand interaction, and so forth. − Integrated with the forces among adsorbent molecules and substrate, molecules could reach the dynamic balance and construct the stable self-assembled molecular arrangements. − The structural self-assemblies of a great many functional organic molecules were researched with scanning tunneling microscopy (STM), − which is a powerful characterization technique with ultrahigh spatial resolution for investigating the molecular self-assemblies at monatomic level in the past few years. , The controlled modulations of the self-assemblies with other organic molecules, , and the host–guest molecular architectures with controlled cavities, − have also been widely studied, especially the networks developed by the hydrogen bonds. , …”

STM Investigation of the Y[C6S-Pc]2 and Y[C4O-Pc]2Complex at the Solution–Solid Interface: Substrate Effects, Submolecular Resolution, and Vacancies

“…For this to occur, the alkane chains of the O–C4 groups must extend up into solution rather than lying flat upon the surface as they do in the open structure. The phenomena of short (≲C12) alkane prosthetic groups failing to adsorb on HOPG are well documented …”

“…The phenomena of short (≲C12) alkane prosthetic groups failing to adsorb on HOPG are well documented. 49 Remarkably, under similar concentration to those used for adsorption on HOPG, the Y[C 6 S-Pc] 2 complex on Au(111) formed three types of molecular arrangements, as shown in Figure 2c,d The cross-like molecule resembles a metallophthalocyanine with peripheral sulfurs, which is the top half of the Y[C 6 S-Pc] 2 complex. High-resolution STM images reveal flat adsorption of the DD complex on both HOPG and Au(111) surfaces, that is, with the ligand planes parallel to the substrate surface (Figure 4), similar to monomeric alkylated phthalocyanines.…”

Regulation of the Assembled Structure of a Flexible Porphyrin Derivative Containing Tetra Isophthalic Acids by Coronene or Different Pyridines

“…Porphyrins and their derivatives have excellent photoelectric properties and have many applications in photocatalysis, sensors, and solar cells . Coronene (COR) is a small guest molecule commonly used in host–guest chemistry, which can form a π–π accumulation effect with the HOPG. , If there is a suitable space in two-dimensional porous nanonetwork, COR will enter the nanocavity and form coadsorption with the host molecule and then rearrange the structure to improve the stability of the coassembly system. − In recent years, research on pyridine regulation for the self-assembly of porphyrin derivatives containing benzoic acid substituents has attracted increasing interest, ,− but there are few reports on pyridine regulation of assembled structures of host molecules containing isophthalic acids due to strong intermolecular hydrogen bonds between host molecules. Li.…”