Chiral Dysprosium-[7]Helicene Macrocycles Showing Record Single-Molecule Magnet Properties in the Lanthanide-Helicene Family.

Chiral helicene-based metal complexes have emerged as an extremely promising class of multifunctional molecules for a wide range of applications. Despite significant progress in the synthesis of helicene-based transition-metal complexes in recent decades, lanthanide species lag far behind and their number is very limited. Compared to the widely studied optical activity and magneto-chiroptical effects, the single-molecule magnet (SMM) properties of lanthanide-helicene compounds, in particular their spin relaxation dynamics, are still largely underexplored. In this work, starting from the chiral Dy(III) hexaazamacrocycles, we prepared the first lanthanide-[7]helicene enantiomers using [7]helicene-2-hydroxy as an axial ligand. The introduction of [7]helicene not only endows the compounds of relatively large molar absorptivities but also land them extremely high thermal stability with decomposition temperature beyond 320 °C. Remarkably, in terms of the traditional metrics of SMMs, these molecules are the best lanthanide-helicene SMMs to date, showing an effective energy barrier (