Controlling Molecular Alignment on Highly Ordered Pyrolitic Graphite of Porphyrin-Tb(III) Double-Decker Single Molecular Magnets

Single molecular magnets (SMMs) that show slow magnetic relaxation properties at low temperatures have great potential for use as nanoscale memory devices or quantum computers. In our study, we focused on porphyrin-Tb(III) double-decker complexes and their magnetic properties.^1,2 Our goal was to control the molecular alignment of SMMs on highly ordered pyrolitic graphite (HOPG) by a self-assembling process. We synthesized protonated, anionic, and radical forms of octaethylporphyrin (OEP)-Tb(III) double-decker complexes and observed the molecular alignment of each molecule on HOPG using scanning tunneling microscopy (STM). The STM observations demonstrated that all OEP-Tb(III) double-decker complexes had similar pseudo-hexagonal packing structure stability on HOPG, regardless of differences in the electronic structure (Figure 1). In particular, the lattice parameters of protonated form 1 (a = 1.41 ± 0.03 nm, b = 1.46 ± 0.05 nm) showed almost the same values as anionic form 2 (a = 1.34 ± 0.01 nm, b = 1.42 ± 0.01 nm) and radical form 3 (a = 1.39 ± 0.04 nm, b= 1.45 ± 0.06 nm).

We also prepared and observed the molecular alignment of a protonated 5,15-bisdodecylporphyrin (BDP)-Tb(III) double-decker complex. This complex showed a lamellar packing structure on HOPG (Figure 2). Herein, we succeeded in isolating stable 2D supramolecular structures of all the OEP-Tb(III) double-decker complexes on HOPG. Control of molecular alignment was also realized by changing the substituents.

References:

 ¹⁾ A. Candini et al., Nano Lett. 2011, 11(7), 2634. 

 ²⁾ D. Tanaka, T. Inose, T. Ogawa et al., Chem. Commun. 2012, 48, 7796.