Research Interests

Chiral Conductors based on Metal-bis(dithiolene) Complexes (Alexandre Abhervé, Flavia Pop, Thomas Cauchy, Narcis Avarvari)

Metal-bis(dithiolene) complexes are an important family of molecular conductors since they usually have a small HOMO-LUMO energy gap and can thus present a metallic band structure under pressure. We designed a series of nickel-bis(dithiolene) complexes based on the chiral dithiolene ligands and performed resistivity measurements under very high pressure using a diamond anvil cell (DAC). We showed that the use of chiral dithiolene ligands with one or two stereogenic centres, together with variation of the counter-ion in the anionic complexes, represents a powerful strategy to modulate the conducting properties of such molecular materials.

Recent Financial Supports:

• SECRETS / ANR PRC / 2020-2025
• ChiraMolCo / ANR PRC / 2015-2020

Metallo-organic porous conducting frameworks (Nicolas Zigon, Narcis Avarvari)

Developed since the late 1980s, metal-organic networks (or MOFs) - constructed by self-assembly of divergent multitopic organic ligands and metal cations or clusters - have demonstrated their ability to provide new materials to meet specific needs. The physico-chemical properties of the resulting material will depend not only on the intrinsic properties of the ligand and metal used, but also on their spatial organisation in the three-dimensional network. MOFs are used in particular for their porosity, which makes them excellent candidates for gas storage or capture, or heterogeneous catalysis. However, few MOFs showing good electrical conductivity and porosity have been described in the literature, despite the growing interest in the development of such materials, which would find their place as sensors or battery electrodes for example.
In the field of conductive MOFs, it is expected that by integrating the TTF parts typically used in organic conductors, materials with conductivities comparable to those of the best organic conductors will be obtained. In this research, we focused on functionalized TTF, TTF-TTP (postdoc - EUR Lumomat 2021-2022) or bisvinylenedithio-TTF BVDT-TTF (thesis 2020-2023 - UA) as ligands. Their extended pi architecture as well as the large number of sulphur atoms favours the orbital overlap between adjacent ligands and thus the conduction of the material. 
The functionalization of BVDT-TTF with 4 pyridines gives a versatile ligand that can be easily combined with several metals (CuII, ZnII, CdII, HgII). In particular, the networks obtained with Cd(II) and halide counterions show a good lateral coverage of the fulvalene entities, as well as a solvent accessible volume of 29%. The pore size is sufficient to allow post-synthetic oxidation by I2 vapour diffusion from single crystal to single crystal, which underlines the stability of the obtained networks. Single crystal conductivity measurements by our collaborator Dr. Pascale Auban-Senzier (Université Paris Saclay) showed an order of magnitude increase in conductivity from 8.0∙10-10 to 6.2∙10-9 S/cm after oxidation. Raman spectrometry measurements performed by our collaborator Dr. Iwona Olejniczak (Institute of Molecular Physics, Polish Academy of Sciences in Poznań, Poland, PHC Polonium partnership), which are a classical way of measuring the oxidation state of fulvalenes, confirmed the oxidation state (+I) in our crystals.

Recent Financial Supports:

• PANDEMIC / ANR JCJC / 2022-2026
• POEMs / EUR Lumomat / 2021-2022
• COCoN / Univ. Angers / 2019-2021

Dithia[7]helicene and dithia-quasi[8]circulene for molecular materials (Flavia Pop, Narcis Avarvari)

Dithia-helicenic structures (helicene and quasi-circulene) which show enantiomeric stability at room temperature are obtained from the same intermediate by intramolecular simple and double dehydrocyclisation reactions. The advantages of their design - thiophene units in the helix and the dithiolone unit fused in the middle of the helix – consist in ease to synthetize and further functionalize. Quasi-circulenes are still rare and in spite of lower stereochemical stability than their helicene counterparts, show peculiar topologies and have never been used in conductive materials. At present these helicene and circulenes are being used in the synthesis of tetrathiafulvalene donors and as ligands in metal-dithiolene complexes for chiral conductors and materials with chiroptical properties.

Recent Financial Supports: 

• AAP CR - Université d’Angers, financement fonctionnement 2 ans, 28k€ (2018−2020)

Circularly Polarized Luminescence of Coordination Complexes (Alexandre Abhervé, Narcis Avarvari)

Attachment of coordinating groups on the helicene platform results in helicene based ligands and corresponding transition metal complexes or lanthanide complexes. We mainly study these compounds for the emission of circularly polarized light (CPL). Synthesis of enantiopure helicene-based bis(pyrazol-1-yl)pyridine ligands (1-bpp) allowed us to prepare chiral Eu(III) complexes with CPL in the visible region. We recently extended our research to other chiral 1-bpp derivatives in the quest of strongly emissive complexes with high dissymmetry factors. 

Chiral diketopyrrolopyrrole (DPP) chromophores and metal complexes (Flavia Pop, Narcis Avarvari)

Chirality has been directly introduced on the N-atom of the DPP (alpha position) for the first time. The impact of the position of the chiral centre with respect with the aromatic core is straightaway seen in their photophysical properties, by solid state luminescence and circular dichroism induced by the proximity of the chiral centre and the aromatic core. These findings give access to new chiral DPPs and open ways to new photophysical and chiroptical properties in solution and solid state. These chiral DPPs are modified with tetraphenylethene (TPE) units to enhance their chiroptical properties (absorption and emission) in the solid state. 
Thiophene diketopyrrolopyrrole (DPP)-2,2’-bpy (bipyridine) ligands with direct link between thiophene and the chelating bpy units afford, or not, ortho-metalation with platinum(II) depending on the substitution scheme of thiophene rings. Coordination of PtII metal ions is investigated with the objective to disclose the type of complexation of a heavy metal and its influence on the photophysical properties of the ligands.

Recent Financial Supports: 

• Contrat postdoctoral 1 an, financement RFI LUMOMAT (2019 - 2020)
• Contrat postdoctoral 1 an, financement mixte RFI LUMOMAT – UBL (2018 - 2019)

Chiral Halide Perovskites (Alexandre Abhervé, Nicolas Mercier)

Chiral Halide Perovskites bring new perspectives for chiroptical applications, such as circularly polarized luminescence (CPL), and spintronic applications. By combining the optoelectronic properties of HP networks with chirality transfer from inserted organic cations, we aim to reveal the potential of chiral halide perovskite materials for CPL and chiro-spintronics. For example, the emergent field of chiro-spintronics proposes to use chiral molecules as a substitute for ferromagnetic materials thanks to the spin-specific interaction between electrons and chiral molecules, a phenomenon called CISS, “chiral-induced spin selectivity”. Chiral HPs are promising candidates in the field thanks to their strong CISS effect. Finally, their strong luminescence makes them candidates for the preparation CP-PeLEDs, devices using a chiral halide perovskite material to produce a circularly polarized electroluminescence.