Switching of Single‐Molecule Magnetic Properties of Tb^III–Porphyrin Double‐Decker Complexes and Observation of Their Supramolecular Structures on a Carbon Surface

Abstract

Double-decker complexes based on single-molecule magnets (SMMs) are a class of highly promising molecules for applications in molecular spintronics, wherein control of both the ligand oxidative states and the 2D supramolecular structure on carbon materials is of great importance. This study focuses on the synthesis and study of 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP)-Tb(III) double-decker complexes with different electronic structures comprising protonated, anionic, and radical forms. Magnetic susceptibility measurements revealed that only the anionic and radical forms of the OEP-Tb(III) double-decker complexes exhibited SMM properties. The barrier heights for magnetic moment reversal were estimated to be 207 and 215 cm(-1) for the anionic and radical forms, respectively. Scanning tunneling microscopy (STM) investigations revealed that these OEP-Tb(III) complexes form well-ordered monolayers upon simple dropcasting from dilute dichloromethane solutions. All three complexes form an isomorphic pseudo-hexagonal 2D pattern, regardless of the differences in the electronic structures of their porphyrin-Tb cores. This finding is of interest for SMM technology as ultrathin films of these materials undergoing chemical transformations will not require any detrimental reorganization. Finally, we demonstrate self-assembly of the protonated 5,15-bisdodecylporphyrin (BDP)-Tb(III) double-decker complex as an example of successful supramolecular design to achieve controlled alignment of SMM-active sites.

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

“…27,28 From molecular modeling calculations, the pore size of a DBA-OC8 hexamer (edge to edge distance) is estimated to be 2.0 nm. This size matches the size of the Tb III (OEP) 2 radical, which, on HOPG, is estimated to be 1.5 nm; 14 consequently, we expect that the Tb III (OEP) 2 radical will fit into the pores of DBA-OC8 (Figure 1c). Based on these modeling results, we investigated bimolecular self-assemblies of a mixture of radical Tb III (OEP) 2 SMMs and DBA-OC8 at the 1-phenyloctane/HOPG interface by STM.…”

“…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.…”

“…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.…”

“…Tb III (OEP) 2 radicals and DBA-OC8 were synthesized by previously reported procedures. 14,30 Details of STM measurements are described in Supporting Information. First the solution of DBA-OC8 in 1-phenyloctane (20¯L, 3.7 © 10 ¹5 M) was drop-cast on HOPG (5 © 5 mm 2 ), and the 2D structures at the solid/liquid interface were observed by STM to ensure the formation of a porous network of DBA (Figure 2a).…”

Molecular lanthanide single-ion magnets: from bulk to submonolayers

“…Finally, it should be noted that related Ln doubledecker complexes were also obtained employing ligands other than Pc, namely tetraphenylporphyrin [106] and octaethylporphyrin [107].…”