Chiral Redox-Active Covalent Organic Cages

This cumulative Ph.D. thesis follows on and expands on fundamental work established on ‶Covalent Organic Cage″ molecules. It is divided into three main topics, which involve sequential studies in porosity, photochemistry, and co-crystallization. A fourth topic presents the synthesis of related molecular species that have not been described yet.
The first topic focuses on the porosity of the cages, which was published in Chemical Science (2021). We reported the synthesis of a series of chiral imine organic cages containing three naphthalene-1,4:5,8-bis(dicarboximide) (NDI) units or pyromellitic diimide (PMDI) units respectively, which were obtained through dynamic imine chemistry. The structures obtained by single-crystal X-ray diffraction analysis for the cages, as well as their textual properties, are described therein. Besides observing that the NDI cage has good selectivity for adsorption of CO2 over N2 and CH4, it appeared that the flexible nature of the PMDI cage in the solid-state resulted in a gate opening phenomenon related to kinetic gas trapping, which is generally observed for soft porous crystals and flexible porous cages.
The second topic of the thesis discusses the investigation of the tunable optoelectronic properties of the cages in photochemistry. As seen in the article mentioned above, the cage incorporating three perylene-3,4:9,10-bis(dicarboximide) (PDI) units displays an efficient delayed fluorescence. In addition, the electrochemical data and the kinetic analysis suggest that a rapid (pseudo)equilibrium establishes between the singlet excited state and the intracage charge-separated state, where two PDI units disproportionate into radical ions. The ensuing manuscript (2022) expands more on this concept and aims to determine the nature of the charge-separated in-depth by state by transient absorption spectroscopy. The experimental data of the rate constants at different temperatures allowed us to calculate the absolute values of driving forces for electron transfer ΔGǂ, reorganization energy λ. In the same manuscript, the fate of the charge-separated state of PDI-cage was also discussed. Our results suggest that no or little PDI triplets form after photoexcitation, and that the back electron transfer is located in the Marcus inverted region.
The third topic of the thesis explores the field of co-crystallization between rationally designed cages and carbon-rich guest molecules. The ensuing manuscript (2022) describes the synthesis of two novel organic cages, in which three methoxy groups are incorporated within the bridging units. Moreover, we show the new cages can be co-crystallized with guest molecules such as C60, C70, or cycloparaphenylene and lead to unprecedented single-crystalline extended fullerene sandwich nanostructures or hierarchical self-assemblies in the solid-state.
Finally, a fourth topic which mainly deals with the design and the synthesis of compounds of interest is presented in the last section of this thesis. In the first part, the synthesis of a series of electron donor-acceptor NDI derivatives will be presented. These species will allow us to perform a comprehensive investigation of the excited-state dynamics. The second part presents the synthesis of a series of di-substituted NDI derivatives possessing different anchoring substituents. These are key building blocks, that were prepared for the formation of the asymmetric chiral imine cages and to further investigate the charge transfer process upon photoexcitation at different wavelengths.
Preceding these three manuscripts and the ending part, the reader will find an introduction in the form of a review entitled ‶Photochemistry Meets Porous Organic Cages″, published in CHIMIA (2021). This tutorial article explains the rise of porous covalent organic cages, due to their three-dimensional aesthetic shapes, with carefully selected examples. Furthermore, it gives a clear systematic overview of the various concepts to depict the potential applications of our organic cages in photocatalysis or solar energy storage.