Publications 2022

We observed efficient induction of chirality in polyfluorene copolymer thin films by mixing with helicene-type chiral additives based on the dibenzo[c,h]acridine motif. Images obtained from circular dichroism (CD) and circularly polarized luminescence (CPL) microscopy provide information about the chiral arrangements in the thin films with diffraction-limited resolution. The CD signal shows a characteristic dependence on the film thickness, which supports a supramolecular origin of the strong chiral response of the copolymer. In particular, we demonstrate the discrimination between films of opposite chirality based on their ultrafast transient chiral response through the use of femtosecond broadband CD spectroscopy and a newly developed setup for transient CPL spectroscopy with 28 ps time resolution. A systematic variation of the enantiomeric excess of the chiral additive shows that the “Sergeants and Soldiers” concept and “Majority Rules” are not obeyed.

Polarization in photonic-integrated circuits (PICs) is governed by transverse electric (TE) and magnetic (TM) polarizations due to the planar structure of the chips. Therefore, all states of polarization (SOPs) other than TE and TM, in particular circular polarization, cannot be routed without modification across the chips. Herein, the realization of rib-channel chirowaveguides supporting elliptically polarized guided modes by combining linear and circular birefringences as predicted by the coupled mode approach is shown. The sol–gel process and the imprint technique to make channel chirowaveguides with different sizes and consequently modulate ellipticity of the eigenmodes from linear to quasicircular are used. Circularly polarized light propagates therefore with a low polarization beating and in particular without handedness inversion. These results open the field of application of PICs to all domains where circularly polarized light is relevant.

We report the synthesis of C3-symmetric cryptophanes decorated with three aromatic amine groups on the same CTB cap and their interaction with xenon. The relative stereochemistry of these two stereoisomers syn and anti was assessed thanks to the determination of the X-ray structure of an intermediate compound. As previously observed with the tris-aza-cryptophanes analogs anti-1 and syn-2 (J. Org. Chem. 2021, 86, 11, 7648–7658), both compounds anti-5 and syn-6 show a slow in–out exchange dynamics of xenon at 11.7 T. Our work supports the idea that the presence of nitrogen atoms grafted directly onto the cryptophane backbone has a strong impact on the in–out exchange dynamics of xenon whatever their stereochemistry. This result contrasts with the case of other cryptophanes decorated solely with methoxy substituents. Finally, we demonstrate that these new derivatives can be used to design new anti/syn cryptophanes bearing suitable ligands in order to constitute potent 129Xe NMR-based sensors. An example is reported here with the synthesis of the tris-iodo derivatives anti-13 and syn-14 from compounds anti-5 and syn-6.

Cryptophane cages can adopt either an anti or syn configuration that present different recognition properties. While the synthesis of anti-cryptophanes is well reported, the synthesis of syn-cryptophanes remains a challenge. Herein, we demonstrate that the use of HFIP as a co-solvent during the second ring closure reaction significantly affects the regioselectivity, providing easier access to the syn-cryptophane stereomers.

A molecular cage-based approach to obtain enantiopure lanthanide complexes with circular polarized luminescence (CPL) activities is presented. Hemicryptophane endohedral complexes were designed by functionalizing the molecular cage with pyridine-2,6-dipicolinamide coordinating groups. Taking advantage of the ability of the inherent chirality of the remote cyclotriveratrylene (CTV) unit to propagate along the linkers of the molecular cage, the encapsulated lanthanide complexes with a controlled chirality have been obtained. In this way, we obtained the CPL active Tb(III) and Eu(III) cages although the chiral CTV unit is located far from the complexation sites. This opens the way for a broader use of enantiopure covalent cages for CPL applications.

Haloazaphosphatranes are the halogenated parents of proazaphosphatranes, also known as Verkade's superbase. While the synthesis of iodo-, bromo- and chloroazaphosphatranes was reported more than thirty years ago by J. G. Verkade, the first synthesis of fluoroazaphosphatranes was only described in 2018 by Stephan et al. Currently, no common and versatile procedure exists to access fluoroazaphosphatranes platform with different structural characteristics. In this report, a new and simple synthesis of this class of compounds was developed based on the nucleophilic attack of the fluoride anion on chloroazaphosphatrane derivatives with good to high isolated yields for the corresponding fluoroazaphosphatranes (70–92%). The scope of the reaction was widened to fluoroazaphosphatranes bearing various substituents and X-ray molecular structures of two of them are reported. The stability of fluoroazaphosphatranes toward nucleophilic solvents like water has been investigated. As they revealed much more robust cations than their chloroazaphosphatrane parents, their chloride salts were tested as organocatalysts for the formation of cyclic carbonates from epoxides and CO2. Fluoroazaphosphatranes proved to be both efficient and stable catalytic systems for CO2 conversion with catalytic activities similar to those of azaphosphatranes, and no decomposition of the cation was observed at the end of reaction.

Different endohedrally functionalized cages were designed to investigate the effects of the size and shape of molecular cavities on the frustrated behavior of Lewis/Brønsted acid–base pairs and on catalytic activities. The shape of the inner space above the reactive center was found to strongly affect these properties. When an acidic azaphosphatrane is inserted in the smallest cage and associated with t-BuOK or −CD2CN bases, a frustrated Brønsted pair is obtained. In contrast, when encapsulated in the medium or large cage, the P–H+ azaphosphatrane acid is easily deprotonated under the same conditions. The resulting two supramolecular Verkade's superbases lead to frustrated Lewis pair systems in the presence of TiCl4. Furthermore, the larger cage displays better catalytic activity in the MBH reaction. Thus, a small change in the cage size, which only differs by one methylene group in the linkers, can influence the frustrated properties of the related systems, and a right balance between the frustrated behavior and cage flexibility has to be reached to obtain optimal systems for catalytic applications.