The main research topics developed in the group of Prof. B. Elias (IMCN/MOST – Supramolecular Photochemistry and Organic Chemistry) are novel light-sensitive molecules for applications in anticancer photodynamic therapy and solar energy conversion. For this purpose, several ruthenium(II)-, iron(II/III)-, osmium(II)-, rhodium(III)- and iridium(III)-based complexes have been synthesized, characterized and subsequently studied.
Investigation of the anticancer activity has been achieved following different strategies, the major one being to use the light to selectively activate the complexes. In particular, one of the current goals of the group is to design complexes that selectively target telomeric G-quadruplex DNA, known to play a key role in the development and propagation of cancerous cells. Some of our complexes have the ability to be sufficiently oxidizing in their excited state to abstract an electron from a DNA base. This electron transfer step can lead to irreversible DNA damages, in turn leading to cell death. In collaboration with the groups of Prof. A. Decottignies (Institut de Duve, UCLouvain), Prof. O. Feron (Institut de Recherche Expérimentale et Clinique, UCLouvain) and Prof. E. Defrancq (Université Grenoble Alpes), we have shown that some of our complexes display increased affinity and selectivity towards G-quadruplex telomeric DNA. Interestingly, they are also able to induce strong photo-cytotoxicity on several types of cancer cells (in cellula studies). Currently, we are investigating this recently developed methodology for in vivo testing in murine models. These studies are carried in close collaboration with the Institut de Duve – UCLouvain (Prof. A. Decottignies and Prof. C. Pierreux).
Regarding solar energy conversion, we have recently developed supramolecular systems composed of Ir(III) or Ru(II) complexes and a catalytic center where hydrogen formation is occuring upon light irradiation, in a range extending from the blue region of the solar spectrum to the red region. This is particularly important as hydrogen is deemed a promising fuel in order to develop a sustainable energy supply. A second approach towards hydrogen photoproduction consists in using complexes to trigger the photooxidation of hydrohalic solutions. This approach can operate with complexes in solution or, as we are also currently developing, grafted on the surface of a semiconductor to develop photo-anodes used in Dye-Sensitized PhotoElectrosynthesis Cells (DSPEC). This would allow to simultaneously perform the oxidation of halides and the reduction of protons into molecular hydrogen. These latter studies are performed in close collaboration with Dr. L. Troian-Gautier, a chargé de recherches F.R.S.-FNRS recently appointed (October 2021) collaborateur scientifique within the IMCN institute.
Species resulting from the assembly of several metallic centers (polynuclear metal complexes) are known for their potential ability to harvest sunlight and transfer it to a specific site. We synthesize and study new supramolecular metallic entities able to transfer light energy from one site of the molecule to another one. We have elaborated different synthetic strategies to obtain multi-terpyridine ligands. These macromolecular units are ideal building blocks for the construction of transition-metal-based supramolecular assemblies. The increased reactivity of sensitizers upon light excitation has contributed to the drastic development of the field of photoredox catalysis, where they have been harnessed to perform challenging organic transformations, difficult to achieve without the use of photoactive catalysts. Ruthenium(II) polypyridyl sensitizers represent attractive candidates as they absorb visible light typically with molar absorption coefficients greater than 10,000 M–1cm–1 and exhibit relatively long-lived excited states.
Finally, we have also used an iron(III) complex for visible light dehalogenation reactions. Iron complexes usually suffer from extremely short excited-state lifetime that usually prevents or limits bimolecular reactivity. We have recently determined key parameters that have allowed to circumvent these limitations and achieve efficient excited-state electron transfer with large cage-escape yields using green light irradiation. Dehalogenation reactions operated with large yields and a clear view of the mechanistic pathway with the associated rate constants was obtained by a combination of time-resolved spectroscopic methods, such as femtosecond and nanosecond transient absorption or infrared spectroscopy (TRIR).
