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Single Molecule Magnets light-switching with photochromic ligands

Periodic Reporting for period 1 - PhotoSMM (Single Molecule Magnets light-switching with photochromic ligands)

Reporting period: 2016-09-01 to 2017-08-31

The integration of molecular-scale components in circuits may ultimately allow the replacement of silicon-based electronics by high speed systems
with low energy consumption. Because of the prominent use of magnetization-based information storage technologies in our daily life, Single-
Molecule-Magnets (SMM), which are able to interconvert between two states with opposite magnetization directions receive a great deal of
attention. The potential is huge for SMM systems that would demonstrate magnetic field- and light-driven changes in both their optical and
magnetic properties because they could reproduce on a single molecule the same type of magneto-optical (MO) effects which are used for some
current data storage technologies. Photo-SMM will demonstrate that a light input can induce a modification of the magnetic and optical properties
of monometallic or bimetallic SMM. This will be achieved thanks to the unprecedented association of anisotropic ions with photochromic ligands
designed to produce very different coordination environments in their two isomeric states, thus maximizing the impact of photo-isomerization on the
ligand field experienced by the 4f or 3d metal ions and on the resulting magnetic behavior.
During the one year outgoing phase at UC Berkeley, research work has been focused on the design and synthesis of new ligands adapted to the photoswitching of lanthanide-based systems.
We have successfully prepared a new linker and the corresponding bimetallic complex. The light-switching behavior of these systems reveal a complex interplay between different parameters, the stability of the photo-induced isomer being impacted by i) metal coordination, ii) solvent or solid matrix environment. This unexpected result prompted us to investigate more into detail these systems and theoretical calculations have been performed in collaboration with this aim. The magnetic investigation of the systems remains to be done.

In parallel, we have prepared new dysprosium complexes which support a terminal dysprosium-fluoride bond and demonstrated that such architectures are excellent in promoting strong axial magnetic anisotropy by combining luminescence, magnetism and ab initio calculations (in collaboration with Boris Le Guennic). A publication is ready to be submitted on this subject and the results have been communicated at the Europen Congress on Molecular Magnetism (Bucarest, August 2017). These new objects are well adapted to the implementation of light switching because they can be assembled by bridging ligands of different type. The next step in this project will then be to test the assembly with different types of photochromic linkers.
We have explored a new type of photochromic ligand based on a pyrazine core and expect to obtain photoswitchable bimetallic systems based on this architecture by the end of the project. The interplay between metal coordination and light switching behavior will be a special point of interest in addition to the obtention of SMM with photomagnetic behavior.

The discovery of lanthanide-fluoride bond as an ingredient of efficient SMM behavior will pave the way for different motivating studies including i) the study of similar complexes with 4f ions other than dysprosium, ii) the desing of supramolecular assemblies with photomagnetic behavior.
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