PhD M/W : "Quadrupolar and octupolar carbo-benzenes: synthesis and mesogenic properties"

Job description

The PhD thesis will take place at the Laboratory of Coordination Chemistry, UPR-8241 of the CNRS in Toulouse, in the team Unsaturated molecules for physics, biology and chemistry under the co-supervision of Remi Chauvin and Valérie Maraval.

This PhD thesis is funded by an International ANR project, and will thus be performed in collaboration with the two Taiwanese partners involved in the project.

Project details

The proposed PhD project is part of an international collaboration for the study of mesophases constituted of molecules, hereafter called "carbo-mesogens", built around a C18 carbo-benzene core. This unprecedented type of core includes the following features: all-carbon composition, hexagonal symmetry, extended flatness, high magnetic aromaticity, "acetylenic" flexibility, empty discotic character (ring diameter ≈ 0.8 nm). Seeking for new types of thermotropic liquid crystals (LCs), the study will focus on carbo-mesogens bearing 2 or 3 dispersive units, each of them bearing 1 to 3 lipophilic chains (alkyl groups, fluorinated or not).

The more general objective is the study of supramolecular assemblies under various conditions, using appropriate analysis tools: crystalline phases (XRD), 3D LC mesophases (POM, DSC, TGA, synchrotron beam PXRD), 2D layer on HOPG surface (STM), in solution (NMR), or in silico (DFT calculations). The work will be systematically conducted in two stages by resorting to the specific expertise of each partner: synthesis and characterization of carbo-mesogens in Toulouse, studies of 3D and 2D mesophases in Taipei. The effects of the variation of the substituents of the carbo-benzene core will be scrutinized. The C18 macrocycle of the latter being more circular than discoid (inner hollow van der Waals diameter = 3.5 Å), inclusion compounds are also naturally envisaged: guest species being supposed to provide specific optical, electric or magnetic properties, metal ions will be more specifically considered.

The relevance of both the project and partnership is based on first results recently published reporting the synthesis, thermotropic properties and 2D supramolecular assemblies of the first carbo-mesogen, and evidencing a rectangular columnar discotic LC behavior at 115°C (Chem. Commun. 2017, 53, 5902).

Preliminary theoretical results also suggest the stability and structural features of carbo-benzene-transition metal cation host-guest associations (Rh(I), Cu(I), Ag(I), Au(I)...)..

The project aims at 4 general objectives (synthesis of carbo-mesogens, delineation of structure-property relationships for 3D and 2D supramolecular assemblies, uncovering of novel types of LCs, appraisal of cooperative effects between carbo-mesogen inclusion complexes), and based on four particular tasks (optimization of quadrupolar carbo-mesogens by variation of the dispersive groups, their position on the macrocycle and the study of carbo-mesogen-transition metal inclusion complexes.

The short term objective in Toulouse is the synthesis of carbo-mesogens bearing different substituents and dispersive groups, whose LC properties will be studied by a PhD student recruited in parallel by our Taiwanese colleagues. The work will allow the recruited PhD student to develop his/her skills both in organic synthesis of complex molecules and in the understanding of the physical phenomena underlying the formation of thermotropic carbo-mesophases and their inclusion derivatives. Their study will open up prospects of application based on properties of various types, optical (LCDs), electrical ((supra)conductive components) or magnetic (LC magnets).

Application process

For any application, please send a CV accompanied by a cover letter.