SMMs are molecules that show slow relaxation of the magnetisation, which can lead to the observation of magnetic hysteresis of molecular origin. SMMs may exhibit a memory effect at the molecular scale and thus present potential applications in high density data storage, spintronic and quantum computing. However the use of molecular magnets is currently locked by one key parameter: the temperatures at which the magnets operate are still far too low since the magnetic poles of the molecules cannot be trapped in one direction. To overcome these limitations, my project proposes to cancel the perturbations on the magnetic moment and the internal magnetic field by isotopic enrichment in free nuclear spin lanthanide and magnetic dilutions.
Lanthanides possess also specific luminescent properties with an emission ranging from the visible to the near infrared spectral range and also a μs-ms luminescence lifetime with large Stoke-shifts (difference between the excitation and emission wavelengths). These unique characteristics generate new applications in material science or bioimaging, in the conception of OLED, in time-resolved luminescent immunoassays, or mono- or biphotonic imaging microscopy. The fundamental point is that both lanthanide magnetism and luminescence have the same origin i.e. the energy splitting of the ground multiplet state. An actual challenge is to combine in the same molecule the SMM property to one or more subsequent physical properties in order to obtain a multifunctional SMM. In my project the lanthanide luminescence will be used as a spectroscopic tool to control and understand the magnetic properties.
The Spin Crossover (SCO) phenomenon occurs in some metal complexes of the first raw. The spin state changes in varying the temperature, the pressure, the magnetic field or in stimulating complexes with light irradiation. While the spin crossover phenomenon occurs at the molecular level, the thermally induced spin transition in the bulk can be accompanied by thermal hysteresis with long-range cooperative interactions between complexes. The change of spin state induced by light irradiation (LIESST: Light Induced Excited Spin State Trapping) is essentially from the Low Spin (LS) to a metastable High Spin (HS) state and is essentially detected at low temperature when one absorbed photon can convert the spin of one metal complex. In my project both thermal (SCO) and light induced (LIESST) magnetic bistabilities will be combined with the memory effect of the SMM behaviour.
Circularly polarized luminescence (CPL) measures the differential spontaneous emission of right-circularly vs. left-circularly polarized light by chiral molecular systems and can be viewed as the emission analogue of circular dichroism (CD). To date, CPL has been used mainly to investigate configurational and conformational changes in chemical and biological edifices because it combines the sensitivity of luminescence measurements and the specificity of the signal for the chiral environment.
MULTIPROSMM, MULtiple PROperties Single Molecule Magnets, aims to combine several physical properties to the single-molecule magnet behaviour to enhance and better understand the magnetic properties to step forward towards potential applications. My project allows the design of original molecular systems able to present magnetic bistabilities under several stimuli (temperature, magnetic field and light) on an unprecedented wide temperature range (very low temperature with Single Molecule Magnet (SMM), intermediate temperature with Light Induced Excited Spin State Trapping (LIESST) and high temperature with Spin Crossover (SCO)) using the luminescence and Circularly Polarised Luminescence (CPL) for the optimal understanding of the magnetic properties. Both isotopic enrichment and shaping will allow the enhancement of the magnetic properties and a step forward towards applications.
