Circularly polarized-thermally activated delayed fluorescent materials based on chiral bicarbazole donors

G. P. thanks the SCBM, the “PTC du CEA” (POLEM) and the ANR (iChiralight, ANR-19-CE07-0040) for funding and David Buisson, Amélie Goudet and Sabrina Lebrequier. J. C. and L. Fa. acknowledge the Ministère de l’Education Nationale, de la Recherche et de la Technologie, the CNRS and the Spectroscopies-CDTP core facility is also acknowledged. The St. Andrews team thanks the China Scholarship Council, 201906250199 to W. S. and 202006250026 to J. W., E. Z.-C. is a Royal Society Leverhulme Trust Senior Research fellow (SRF\R1\201089). We thank the EPSRC (EP/R035164/1) for funding.We describe herein a molecular design to generate circularly polarized thermally activated delayed fluorescence emitters in which chiral bicarbazole donors are connected to acceptor units via a rigid 8-membered cycle and how the nature of the donor and acceptor units affect the photophysical and chiroptical properties.Publisher PDFPeer reviewe

Conception de systèmes organiques chirales persistants à couche électronique ouverte fondés sur des motifs de type carbazole

Les matériaux chiraux π-conjugués ont récemment émergé comme une voie prometteuse en science des matériaux en raison de leur interaction spécifique avec la lumière polarisée circulairement et du potentiel de cette dernière dans plusieurs domaines d'applications tels que les diodes électroluminescentes organiques (OLED), les transistors organiques à effet de champ (OFET) et la spintronique moléculaire. Les nombreuses recherches sur cette thématique se concentrent actuellement sur des systèmes chiraux organiques avec une configuration électronique à couche fermée, et peu d’études ont exploré leurs homologues à couche ouverte (radicaux), vraisemblablement en raison de leurs problèmes de réactivité et de stabilité. Ce travail de thèse s’inscrit dans cette problématique et vise à développer de nouveaux radicaux intrinsèquement chiraux stables à base de carbazole. Nous avons exploré de nouveaux designs moléculaires conduisant à des radicaux chiraux cationiques à caractère persistant, résultant d’un processus d'inversion orbitalaire entre les niveaux SOMO et HOMO (SHI pour SOMO/HOMO inversion). L’obtention de cette configuration électronique peu usuelle nous a permis de mettre en avant certains paramètres clés régissant la stabilité des espèces radicalaires obtenues. Nous avons étendu cette approche à diverses structures radicalaires cationiques et neutres, aboutissant à la génération de mono- et di-radicaux chiraux cationiques et neutres inédits et relativement stables, présentant à la fois un intérêt fondamental et également applicatif dans des dispositifs opto-électronqiues.Chiral π-conjugated materials have recently emerged as a promising direction in materials science due to their specific interaction with circularly polarized light and the potential of the latter in several domains of applications such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and magnets. While extensive researches have been focusing on organic chiral dyes with closed-shell electronic configuration, few attentions have been paid on their open-shell counterparts (radicals), presumably because of their reactivity and stability issues. This thesis has aimed to develop novel intrinsic chiral radicals based-on carbazole moiety. We explored a new molecular design of persistent intrinsically chiral organic radicals via a SOMO-HOMO level inversion (SHI) process. This electronic configuration allowed us to highlight certain key parameters governing the stability of the obtained radical species. We have extended this approach to various cationic and neutral radical structures, resulting in the generation of novel and relatively stable cationic and neutral chiral mono- and di-radicals, presenting both fundamental and promising directions in opto-electronic applications

Merging Electrocatalytic Alcohol Oxidation with C-N Bond Formation by Electrifying Metal-Ligand Cooperative Catalysts

The development of energy and atom efficiency processes is thought to play an important role for a sustainable chemical industry of the future. One opportunity could be the electrification of thermal processes to benefit from the inherent advantages of electrochemistry, such as safety, scalability, a cheap and traceless redox agent (electrons), and the possibility to directly control the energy input of a given reaction via the applied potential. Molecular electrocatalytic alcohol oxidation emerged as a powerful tool for energy efficient redox transformations with possible applications in both green synthesis and energy-relevant domains. Using transfer hydrogenation catalysts under electrochemical conditions was shown to be promising avenue in this respect, but is today limited in terms of substrate scope. Here, we reported the electrification of acceptor-less dehydrogenation catalysts for the coupling of alcohol oxidation with C-N bond formation. Imines are thus obtained with excellent selectivity and faradaic efficiency, showing a possibility route towards added-value products from simple building blocks. We hope that the successful electrification of such atom-efficient systems can contribute to a more energy efficient organic redox chemistry

La chiralité à la lumière des matériaux moléculaires, une nouvelle direction pour l'électronique organique

National audienceUbiquitous in our world, the property of chirality at the molecular level is a crucial element in drug discovery and development, owing to its fundamental role in biological processes. More recently, this molecular dissymmetry[1] has been extended to the research domain of molecular materials, providing them with innovative properties such as a specific interaction with a circularly polarized light. Given the potential of the latter in several research domains including display applications, cryptography, bio-imaging and spintronics, chiral molecular materials have recently attracted considerable attention as innovative CPL emitters. This latter aspect is notably illustrated in this article with selected examples of -conjugated helical architectures, investigated within the 'Organométalliques : Matériaux Moléculaires et Catalyse' team (OMC) at the Institut des Sciences Chimiques de Rennes (UMR 6226 CNRS - Université de Rennes), opening new opportunities in “chiral” organic electronics.Omniprésente dans notre monde, la propriété de chiralité à l'échelle moléculaire est un élément majeur dans la découverte et le développement de médicaments du fait de son effet sur l'activité biologique. Plus récemment, cette dissymétrie moléculaire [1] s'est étendue au domaine des matériaux organiques en leur conférant des propriétés inédites, telles qu'une interaction spécifique avec une lumière dite circulairement polarisée. Du fait du potentiel de cette dernière dans différents domaines d'applications incluant les technologies d'affichage, la cryptographie, l'imagerie biologique ou encore la spintronique, un intérêt grandissant est porté sur les matériaux chiraux luminescents en tant qu'émetteurs de lumière circulairement polarisée. Cette dernière particularité est discutée dans cet article au travers d'exemples d'architectures moléculaires hélicoïdales développées ces dernières années au sein de l'équipe 'Organométalliques : Matériaux Moléculaires et Catalyse' (OMC) à l'Institut des Sciences Chimiques de Rennes (UMR 6226 CNRS-Université de Rennes), laissant entrevoir de nouvelles perspectives en électronique organique « chirale »

Catalyst Complexity in a Highly Active and Selective Wacker-Type Markovnikov Oxidation of Olefins with a Bioinspired Iron Complex

International audiencePalladium-catalyzed Wacker-type reactions occupy a central place in organic synthesis with important implications in industry. Pursuing more benign protocols by replacing palladium by first-row transition metals allowed the identification of iron as a privileged one in the last years. Although the anti-Markovnikov selectivity for iron catalysts is well developed, the Markovnikov-selective reactions still afford significant quantities of alcohol side-products and identification of reaction intermediates remains elusive so far. Herein, we present an iron catalyst that affords Markovnikov ketone products from (hetero)aromatic and aliphatic olefins in up to 99% selectivity under ambient conditions with 190,000 turnover numbers and turnover frequencies of 74 h-1 at 50 o C. The catalyst design is based on the promiscuous activity encountered in the family of the cytochromes P-450 enzymes and it enables the formation of iron-hydride species under catalytically relevant reaction conditions. Substrate scope assessment and mechanistic investigations suggest that the Markovnikovselective catalytic cycle competes with unprecedented three additional catalytic cycles (alcohol formation, hydrogenation and reductive homo-coupling) depending on the nature of the olefin and the reaction conditions

Remote ion-pair interactions in Fe-porphyrin-based molecular catalysts for the hydrogen evolution reaction

International audienceThe environmentally benign production of clean energy is extremely important for the sustainable progress of our society. In this respect, dihydrogen (H2) has been considered in the last decades as an efficient energy carrier and much effort has been directed to the hydrogen evolution reaction (HER). Herein, we report on the efficiency of iron-based 5,10,15,20-tetraphenylporphyrins containing carboxylate groups in different positions (ortho, meta and para of the meso-substituted aryl groups of the porphyrin backbone) as molecular catalysts for the HER. The iron-based porphyrin containing the carboxylic acids in the ortho position was found completely inactive in the HER. Furthermore, besides stereoelectronic control, the subtle differences observed in the cyclic voltammograms (CV) as well as those associated with the electrocatalytic activity might involve a previously neglected ion-pair interaction between the carboxylate groups of the porphyrin scaffold and the chloride anions belonging to the proton source, which highlights the relevance of ion-pair contacts remote from the active center for this type of catalytic system

Organic radicals with inversion of SOMO and HOMO energies and potential applications in optoelectronics

International audienceOrganic radicals possessing an electronic configuration in which the energy of the singly occupied molecular orbital (SOMO) is below the highest doubly occupied molecular orbital (HOMO) level have recently attracted significant interest, both theoretically and experimentally. The peculiar orbital energetics of these SOMO-HOMO inversion (SHI) organic radicals set their electronic properties apart from the more common situation where the SOMO is the highest occupied orbital of the system. This review gives a general perspective on SHI, with key fundamental aspects regarding the electronic and structural factors that govern this particular electronic configuration in organic radicals. Selected examples of reported compounds with SHI are highlighted to establish molecular guidelines for designing this type of radical, and to showcase the potential of SHI radicals in organic spintronics as well as for the development of more stable luminescent radicals for OLED applications

Luminescent chiral exciplexes with sky-blue and green circularly polarized-thermally activated delayed fluorescence

International audienceLuminescent exciplexes based on a chiral electron donor and achiral acceptors are reported as a new approach to design circularly polarized (CP) and thermally activated delayed fluorescence (TADF) emitters. This strategy results in rather high CP luminescence (CPL) values with g$_{lum}$ up to 7x10$^{-3}$, one order of magnitude higher in comparison to the CPL signal recorded for the chiral donor alone g$_{lum}$ similar to 7x10$^{-4}$. This increase occurs concomitantly with a CPL sign inversion, as a result of the strong charge-transfer emission character, as experimentally and theoretically rationalized by using a covalent chiral donor-acceptor model. Interestingly, blue, green-yellow and red chiral luminescent exciplexes can be obtained by modifying with the electron accepting character of the achiral unit while keeping the same chiral donor unit. These results bring new (inter)molecular guidelines to obtain simply and efficiently multi-color CP-TADF emitters

Carbazole Isomerism in Helical Radical Cations: Spin Delocalization and SOMO–HOMO Level Inversion in the Diradical State

International audienceWe report a new molecular design to afford persistent chiral organic open-shell systems with configurational stability and an inversion in energy of the singly occupied molecular orbital (SOMO) and the highest doubly occupied molecular orbital (HOMO) for both mono- and diradical states. The unpaired electron delocalization within the designed extended helical π-conjugated systems is a crucial factor to reach chemical stabilities, which is not obtained using the classical steric protection approach. The unique features of the obtained helical monoradicals allow an exploration of the chiral intramolecular electron transfer (IET) process in solvents of different polarity by means of optical and chiroptical spectroscopies, resulting in an unprecedented electronic circular dichroism (ECD) sign inversion for the radical transitions. We also characterized the corresponding helical diradicals, which show near-infrared electronic circular dichroism at wavelengths up to 1100 nm and an antiferromagnetic coupling between the spins, with an estimated singlet–triplet gap (ΔEST) of about −1.2 kcal mol–1. The study also revealed an intriguing double SOMO–HOMO inversion (SHI) electronic configuration for these diradicals, providing new insight regarding the peculiar energetic ordering of radical orbitals and the impact on the corresponding (chiral) optoelectronic properties

Axially and Helically Chiral Cationic Radical Bicarbazoles: SOMO-HOMO Level Inversion and Chirality Impact on the Sta- bility of Mono-and Diradical Cations

International audienceWe report persistent chiral organic mono-and diradical cations based on bicarbazole molecular design with an unprecedented stability dependence on the type of chirality, namely axial versus helical. An unusual chemical stability was observed for sterically unprotected axial bicarbazole radical, in comparison with monocarbazole and helical bicarbazole ones. Such results were experimentally and theoretically investigated, revealing an inversion in energy of the singly occupied molecular orbital (SOMO) and the doubly highest occupied molecular orbital (HOMO) in both axial and helical bicarbazole monoradicals, along with a subtle difference of electronic coupling between the two carbazole units, which is modulated by their relative dihedral angle and related to the type of chirality. Such findings allowed us to explore in-depth the SOMO-HOMO inversion (SHI) in chiral radical molecular systems and provide new insights regarding its impact on the stability of organic radicals. Finally, these specific electronic properties allowed us to prepare a persistent, intrinsically chiral, diradical which notably displayed near infrared electronic circular dichroism responses up to 1100 nm and almost degenerate singlet-triplet ground states with weak antiferromagnetic interactions evaluated by magnetometry experiments