Deux articles sur les polymorphes

L'élaboration de matière artificielle est un sujet de plus en plus étudié. L'objectif est de créer des surfaces fonctionnelles qui ne peuvent être qu'acessibles que par le confinement de moélcules sur des surfaces.

Nous venons de publier deux exemples de polymorphes qui ne peuvent être qu'obtenus qu'en déposant des molécules soit sur une surface isolante soit sur une surface de graphène/Iridium.

Pour la partie sur Graphène, nous avons collaboré avec l'institut Jean Lamour (Nancy) et le LPCNO de Toulouse et pour la partie sur isolant avec l'IM2NP (Marseille) et le département de Physique et d'Astronomie de University College of London.

 

Graphène ;  J. Phys. Chem. C 2017, 121, 2201−2210

 

The properties of two-dimensional supramolecular self-assemblies on surfaces depend on the fine balance between molecule− substrate and molecule− molecule interactions. In this article, we study the growth of 1,3,5-tri(4′ - bromophenyl)benzene (TBB) monolayer on graphene epitaxially grown on Ir(111) by means of low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) combined with a fully atomistic description of the molecules in interaction with the Gr/Ir(111) substrate, using density functional theory (DFT). In order to figure out the impact of the underlying metallic layer upon the self-assembling behavior of the molecules and their properties, we compare our results with those theoretically obtained on pristine graphene or experimentally achieved on highly oriented pyrolytic graphite (HOPG). We demonstrated that the use of the Ir layer allows the formation of large extended, continuous, and two-dimensional supramolecular networks lying even over Ir step edges like a carpet. In addition, we highlighted the obtention of two structural polymorphs never observed on HOPG. In the light of DFT simulations, we assumed that the formation of these polymorphs is driven by the balance between molecule− molecule interactions, due to halogen bonds (XB), and the tailored molecule− surface interactions due to the presence of Ir layer.

 

Isolant : J. Phys. Chem. C 2017, 121, 4393−4403

 

We studied the eff ect of molecular fl exibility on the morphology and growth mechanisms of self-assembled fi lms on an insulating substrate using a combination of experimental and theoretical methods. 1,3,5-Tri-(4-cyano-4,4biphenyl)-benzene (TCB) and 1,4-bis(cyanophenyl)-2,5-bis- (decyloxy) benzene (CDB) molecules were deposited on a KCl (001) surface and imaged using noncontact atomic force microscopy (NC-AFM). Both molecules were designed to contain the same anchoring groups and benzene ring structures, yet CDB self-assembled structures were observed to grow from step edges, while TCB self-assembled structures grew as islands on the clean terrace and from step edges. Density functional theory (DFT) and atomistic molecular dynamics simulations were performed to understand this qualitative diff erence in growth modes. Calculations of free energies of dimer formation and step adhesion provide an insight into the role played by entropy loss in the morphology and growth modes of self-assembled films.