Spontaneous Assembly and Three‐Dimensional Stacking of Antiaromatic 5,15‐Dioxaporphyrin on HOPG

Abstract

Antiaromatic compounds have recently received considerable attention because of their novel properties such as narrow HOMO-LUMO gaps and facile formation of mutual stacking. Here, the spontaneous assembly of antiaromatic meso-2-thienyl-substituted 5,15-dioxaporphyrin (DOP-1) is scrutinized at the liquid-solid interface by scanning tunneling microscopy (STM). Polymorphism in monolayers characterized by the orthogonal and parallel assemblies is found at the low concentration of 0.05 mM. The parallel assembly is more stable and dominantly formed at higher concentrations. Aggregation was observed at concentrations > 0.2 mM, and the STM images of the aggregates implied the formation of stacked layers. The intrinsic electronic structures of the mutually stacked bilayer generated by applying an electric pulse to the monolayer were probed by scanning tunneling spectroscopy to reveal the narrowing of the HOMO-LUMO gap by about 20 % compared with the monolayer, thus suggesting significant molecular orbital interactions.

A Paradigm Shift from 2D to 3D: Surface Supramolecular Assemblies and Their Electronic Properties Explored by Scanning Tunneling Microscopy and Spectroscopy

“…Molecular manipulation of sandwich doubledecked complexes and construction of assemblies at the liquidsolid interface can also be achieved by STM analysis. [131,132] Small 2023, 19, 2300413 [126] Copyright 2022, Wiley-VCH. b) Reproduced with permission.…”

“…b-3) Small-scale STM images and energy-minimized clockwise structure of the bilayer arrangement of (L)-FAC18. a) Reproduced with permission [126]. Copyright 2022, Wiley-VCH.…”

Recent advances in the synthesis of diazaporphyrins and their chalcogen derivatives

“…In a recent study by Shimizu et al , the spontaneous assembly of 111 (Ar = 2-thienyl) was studied at the liquid–solid interface to elucidate its polymorphism in a monolayer and the facile formation of the stacked layer. 77…”

Frontier Orbital Views of Stacked Aromaticity

“…Theoretical studies have also shown that orbital switching occurs when the π-stacking distance of Ni(II) norcorrole face-to-face stacking is reduced to 3.0 Å . On the other hand, scanning tunneling spectroscopy shows that the HOMO–LUMO gap of the bilayers in antiaromatic meso -2-thioethyl-substituted 5,15-dioxaporphyrin is smaller than that of monolayers (Scheme b) . These results show different properties, although the antiaromatic molecules are stacked.…”

“…26 On the other hand, scanning tunneling spectroscopy shows that the HOMO−LUMO gap of the bilayers in antiaromatic meso-2-thioethyl-substituted 5,15-dioxaporphyrin is smaller than that of monolayers (Scheme 1b). 27 These By focusing on the π-stacking distance and the change in molecular orbitals, it might be possible to clarify whether stacking aromatization occurs or not. In this study, we investigated the changes in aromaticity and molecular orbitals for fully stacked dimer models with cyclobutadiene, which is the simplest antiaromatic molecule, and we adopted density functional theory (DFT) 28,29 calculations.…”