Coadsorption of Tb^III–Porphyrin Double-decker Single-molecule Magnets in a Porous Molecular Network: Toward Controlled Alignment of Single-molecule Magnets on a Carbon Surface

Abstract

A self-assembled monolayer of a mixture of radical 2,3,7,8,12,13,17,18-octaethylporphyrin 8,9 In studies of nanocarbon/SMM composites, spin valve effects are important, and the magnetic state of SMMs on nanocarbon materials can be detected by electrical signals. Here, we report the first successful detection of the magnetic states of SMMs on a 2D surface. Research into nanocarbon/SMM composites is of great interest for technological applications of SMMs, such as high-density data storage. In this context, controlling the two-dimensional (2D) supramolecular structure of SMMs on a surface is extremely important for these composite materials because differences in the 2D structures of SMMs are expected to affect the intermolecular magnetic dipole moment; however, there are few reports describing the 2D structures of SMMs at the molecular level.1012 Correct fabrication of 2D supramolecular complexes is a significant step toward the realization of SMM applications such as high-density molecular memory devices.Previously, we focused on porphyrinTb III double-decker (Por-DD) SMMs because of their high functional group tenability and unique proton-induced magnetic switching properties, and because the SMM properties of their anionic and radical forms are comparable to those of other reported SMMs.13,14 Moreover, we succeeded in constructing regular 1D and 2D supramolecular structures of Por-DD complexes on highly oriented pyrolytic graphite (HOPG) surfaces that have good magnetic switching properties. This was achieved by introducing alkyl groups to the porphyrin core to enhance the interaction between the molecule and the HOPG surface.14 Moreover, a scanning tunneling microscopy (STM) study of a 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP)Tb III double-decker (Tb III (OEP) 2 ) complex with three different electronic structures, i.e., protonated, anionic, and radical forms, revealed that these complexes form stable pseudohexagonal packed structures with similar lattice parameters. STM is one of the most powerful tools for the investigation of 2D molecular networks at the sub-molecular level, and many 2D supramolecular structures in different environments have been observed by STM. 1525 Herein, we demonstrate a new approach for further control over the 2D SMM structures on graphitic surfaces using Tb III (OEP) 2 radicals. The Tb III (OEP) 2 radical is planar and neutral; therefore, it does not have a counter ion, and this simplifies the STM measurements in comparison to those of the Tb III (OEP) 2 anion. Because the surface-confined pores in the 2D porous molecular network are known to immobilize other molecules as guests, 13,14,19,2326 the surface periodicity and density of the SMM molecule can be controlled by its coadsorption in a porous molecular network. For this purpose, we chose alkoxylated dehydrobenzo [12]annulene (DBA) derivatives 2629 because these are reported to form porous networks at liquid/solid interfaces via alkyl chain interdigitation (van der Waals interactions) with adjacent molecules. One of ...

Supramolecular structures of terbium(iii) porphyrin double-decker complexes on a single-walled carbon nanotube surface

“…51,52 Tb III -porphyrin double-decker complexes have an important feature: they are present in three forms, i.e., protonated, anionic, and radical forms (Schemes 1 and S1 †), and the electronic and magnetic properties of these forms can be switched as reversible interconversion between these forms is possible. 48,51 Although the supramolecular structures of lanthanidetetraazolic-based double-decker complexes on at nanocarbon surfaces, i.e., HOPG, have been extensively studied, 45,46,[53][54][55][56][57][58] the self-assembly of arrays on the curved carbon surfaces of SWNTs has not been reported yet, and it remains difficult to predict and understand the structures. However, some attempts have been made to reveal the chemistry needed to bridge the carbon nanotubes and double-decker domains.…”

Construction of a two-dimensional metal–organic framework with perpendicular magnetic anisotropy composed of single-molecule magnets

“…The selfassembly of molecules using weak intermolecular interactions enables the construction of well-ordered and clean molecular nanosheet. 22 Similarly, coadsorption of lanthanoid phthalocyaninato double-decker complexes (Tb 3+ , Dy 3+ and Ho 3+ complexes behave as SMM 3,23 ) and the supramolecular network 24 is an alternative method to construct SMM nanosheets. However, it is difficult to predict the resultant structures and achieve large surface coverage while controlling the number of layers.…”

Redox‐Driven Symmetry Change for Terbium(III) Bis(porphyrinato) Double‐Decker Complexes by the Azimuthal Rotation of the Porphyrin Macrocycles

“…[35,36] Recently,weh ave investigated the SMM behavioro ft erbium bis(porphyrinato) double-decker complexes and their self-assembly on surfaces, with the aim of achieving SMM-based molecular devices. [37][38][39][40] They exhibit unique reversible ON/OFF switching of the SMM behaviorb yp rotonation/deprotonation. [37,38] The protonated form does not exhibit SMM behavior at any temperature range, whereas both the anion and radical forms exhibit SMM behavior.A ttachment of ap roton to one of the eight nitrogen atoms of the ligand significantly decreases the symmetry of the coordination geometry aroundt he terbium ion, [37,41] which leads to the disappearance of SMM properties for the protonated form.…”

“…Recently, we have investigated the SMM behavior of terbium bis(porphyrinato) double‐decker complexes and their self‐assembly on surfaces, with the aim of achieving SMM‐based molecular devices . They exhibit unique reversible ON/OFF switching of the SMM behavior by protonation/deprotonation .…”