Synthesis of spin crossover micro-and nano-particles and study of the effect of their sizes and morphologies on their bistability properties

Nowadays, the idea that molecule can be used as an active element in an electronic device stimulates scientific activity of chemistry and physics laboratories worldwide. The information storage capacity from technological demands is growing exponentially, which relies much on the development of nanosciences. The objective is to store data as quickly as possible in a device as small as possible. One of the most promising strategies is based on the concept of molecular bistability, the switching between two electronic states of a molecule in the same way that a binary switch. It is thus possible to pass in a reversible and detectable manner from one state (OFF = 0) to another state (ON = 1) under the influence of a controlled external stimulus. The spin transition (ST) phenomenon that switches the system between high spin (HS) and low spin (LS) states is a typical example of molecular bistability. The two states can be distinguished with different magnetic, optical and structural properties and can be induced by an external perturbation like the temperature, the light, the pressure, a magnetic field or the inclusion of a guest molecule. When the structural changes associated with the spin transition are transmitted in a cooperative manner across the network molecules, the transitions will occur with steepness and possibly accompanied by hysteresis loop (the first order transition). So, spin transition molecular materials should offer many opportunities in terms of applications in the field of electronics, information storage, digital display, photonics and photo-magnetism. Among the different families of compounds, coordination polymers arouse much interest due to their bistability near room temperature. The judicious choice of ligands and counter-anions make possible to modulate the final properties of these compounds and even in some cases to synergistically combine different physical properties. The work developed in this thesis attempt to address the different issues related to the challenge of coordination polymers based nanoscale materials with spin transition. The synthesis of inorganic bistable materials, their development in micro- and nanoparticles, thin layers, their organization and their physical properties are shown. The materials in the microscopic scale have mostly the same physical properties as those measured at the macroscopic scale. However, at the nanoscale, materials can exhibit physical properties that are far from those of bulk compounds. It is therefore imperative to understand more about the phenomena related to material size decrease to develop nanotechnology. The fundamental study of these nanomaterials is necessary and represents a major challenge today, which is of prime importance for the development of future applications. The development of nanoscale materials through the control of certain systematic models permits to improve our understanding of specific effects at the nanoscale. For example, in the case of spin crossover complex, the most important question is: how downsizing effect influences the transition temperature, the cooperativity and the width of hysteresis loop? In this context, this thesis is devoted to the design and the synthesis of various size spin crossover nano and micro-materials with different morphologies. To accomplish this, we developed the reverse-micelle technique and adopted innovative matrix-free synthetic approaches.