■ Metal-Organic Frameworks (MOFs) - Spin Crossover Complexes (SCO) hybrid architectures for sensing applications

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Description of the PhD project

Metal-Organic Frameworks (MOFs) are ideal materials for the modular design of complex assemblies, as they possess a long-range ordered hybrid structure associated with well-organized micro- or mesoporous channels and/or cages. Their chemical composition can be easily tuned, through direct or post-synthetic methods, as well as the presence of redox, photoactive or acid/base centers within the framework. This large chemical versatility combined with the huge structural diversity, offers a unique opportunity to generate a diversity of structures and compositions, making them of great interest for various applications such as gas storage, separation, catalysis, drug delivery, etc. Several MOFs can be used for the selective sensing of small molecules, mainly through the modulation of their emissive properties, but the limited stability of these systems prevents them for being used in real devices.
Taking into account the ability of porous MOFs to encapsulate various types of guest molecules, like metal-coordination complexes, into their porosity, this project aims at a novel route to develop sensing materials, i.e. the inclusion of spin crossover complexes (SCO) inside the pores of MOFs. Indeed, SCO complexes are capable of switching their spin states upon external stimuli such as temperature. This switching phenomenon is accompanied by change in many physical properties such as color, magnetic susceptibility, etc. making them promising candidates for technological applications such as molecular switches and sensors. The encapsulation of such complexes in the pores of MOFs remains almost unexplored to date while one can expect not only the SCO complexes properties to be exploited and even enhanced by confinement effects but also to be modulated through the selective sorption of guests in the MOFs, which would lead to enhanced sensing properties.
The MOF-SCO hybrid solids will be prepared by incorporating some designed SCO complexes in the pores of robust MOFs. Diamagnetic water stable MOFs with pores larger than 10 Å will be selected as host matrices. We will focus on diamagnetic large pores MOFs like MIL-100(Al) and new mesoporous Zr(IV) based MOFs currently under development in the group. Regarding to the spin crossover complexes, we will select systems exhibiting a good stability, a thermal switching in solution close to room temperature and easy ways of functionalization. These complexes will be functionalized to tune their supramolecular interaction (π-stacking, H-bond…) with the host framework in order to obtain hybrid solids presenting a thermal spin transition close to room temperature. The influence of guest molecules sorption on the spin state of the complexes will then be probed. In particular, we will focus our attention on volatile organic compounds (VOCs) such as aldehydes, carboxylic acids or aromatic hydrocarbons. The most sensitive solids will finally be shaped as thin films to go towards the design of sensing devices.

Keywords

Metal Organic Frameworks, synthesis, coordination complex, spin crossover, luminescence, sensing, volatile organic compounds, thin films

Research unit

FRE2000 Paris Porous Material Institute

Description of the research Unit/subunit

The project will be performed at the Institut des Matériaux Poreux de Paris, which is a joint CNRS-ENS-ESPCI laboratory created in September 2016 that possesses a strong expertise in the design, synthesis optimization (down to the nanoscale), and shaping of Metal Organic Frameworks (MOFs) for applications ranging from separation, catalysis, energy, sensing and health. State-of-the-art world-class scientific facilities are available in the group or at the ENS and ESPCI, ideally suited to the successful development of the project. Among them, the following are outlined laboratories for organic and inorganic synthesis including Teflon lined reactors for solvothermal synthesis, batch reflux scale-up reactors, X-ray powder diffractometers for routine characterization, high throughput and high resolution analysis, PDF and temperature dependent analysis, Nitrogen porosimeters and spectroscopic facilities (UV-Vis, fluorescence, FT-IR…). A fluorimeter equipped with a vapor adsorption chamber is expected to be acquired in a near future (ESPCI).

Name of the supervisor
Antoine Tissot (antoine.tissot (arobase) espci.fr)

Name of the co-supervisor
Christian Serre (christian.serre (arobase) espci.fr)

3i Aspects of the proposal

During the past decade, researchers from IMAP have produced series of functional MOFs or MOFs nanoparticles in a view of potential applications in various fields (adsorption, sensing, catalysis, health…), requiring a strong crossover of expertise (chemical engineers, materials scientists, biologists, pharmacists…). This project represents another fascinating opportunity to assess the potential of MOFs in the field of sensing. It will be at the interface between synthetic chemistry, as it will involve the synthesis of coordination complexes, MOFs and hybrid solid and solid-state physics, as an important part of the project will be devoted to the characterization of the switching properties of the designed solids by a combination of magnetic measurements (performed at LPEM, ESPCI), spectroscopies (UV-Vis, luminescence, EPR…) and advanced X-Ray diffraction experiments (high-resolution PXRD, synchrotron based SCXRD, PDF…). The combination of both synthesis and advanced characterization of the solids will be a keypoint for the project. Indeed, understanding how the structure of the solids affects their switching behavior and therefore, their sensing ability, will be necessary in order to design materials with “improved” properties. This strategy based on the interplay between physics and chemistry will definitely be an asset to design materials presenting sensing properties (sensitivity, selectivity…) beyond the state of the art, which may further be integrated into real sensing devices.
Dr. Serre and Dr. Tissot have developed during the past decade a very strong international network in the fields of MOFs and their applications and of switchable solids throughout Europe or Asia. One could therefore establish here collaboration with foreign research teams expert in the study of the switching mechanism of the solids developed in the project, for example with the Physical Chemistry Department of the University of Geneva (Switzerland), expert in photophysics and photocrystallography. A possibility would be to send the PhD candidate for a research journey in the team in order to finely characterize the best materials identified through this project. At longer term, this could set the basis of a new EU H2020 project.

Expected Profile of the candidate

Ideally, the candidate shall either possess a first experience both in the synthesis and characterization of materials (porous or dense) or in molecular coordination chemistry. A good sense of communication, a will to work in a multidisciplinary team, the use of office tools and a high level in English are also expected.

Important dates

Call for applications : from July 16th to September 17th 2018
Eligibility check results : Late September
3i Committee evaluation results : Late October
Interviews from the shortlisted candidates with the Selection Committee : Mid-December (week of December 10th)
Final results : Late December





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