Chiral Organometallic Complexes Derived from Helicenic N -Heterocyclic Carbenes (NHCs): Design, Structural Diversity, and Chiroptical and Photophysical Properties - Archive ouverte HAL
Article Dans Une Revue Accounts of Chemical Research Année : 2024

Chiral Organometallic Complexes Derived from Helicenic N -Heterocyclic Carbenes (NHCs): Design, Structural Diversity, and Chiroptical and Photophysical Properties

Résumé

Recently, helicene derivatives have emerged as an important class of molecules with potential applications spanning over asymmetric catalysis, biological activity, magnetism, spin filtering, solar cells, and polymer science. To harness their full potential, especially as emissive components in circularly polarized organic light-emitting diodes (CP-OLEDs), generating structural chemical diversity and understanding the resulting photophysical and chiroptical properties is crucial. In this Account, we shed light on the chemical engineering combining helicene and N-heterocyclic carbene (NHC) chemistries to create transition metal complexes with unique architectures and describe their photophysical and chiroptical attributes. The donating and π-accepting capabilities of the helically chiral -conjugated NHCs endow the complexes with remarkable structural and electronic features. These characteristics manifest in phenomena such as chirality induction, very long-lived phosphorescence, strong chiroptical signatures (electronic circular dichroism and circularly polarized luminescence).

We describe the different classes of ligands primarily developed in our group, by classifying them according to their connection between the helicenic moiety and the imidazole precursor. This connection is essential in determining the degree of π-conjugation and characterizing the emissive state. We comprehensively discuss 6-coordinate, 4-coordinate, and 2-coordinate complexes, delving into their structural nuances and examining how the interplay between metals and auxiliary ligands shapes their photophysical properties, with interpretations enriched by DFT calculations. Helicenes are known to promote intersystem crossing thanks to strong spin-orbit coupling while metals offer robust frameworks leading to a variety of molecular architectures with specific topologies together with distinct excited state properties. The electronic configurations and energy levels of ligand and metal orbitals thus significantly modulate the photophysical and chiroptical behaviors of these complexes. In-depth analysis of chiroptical properties, notably electronic circular dichroism and circularly polarized luminescence, emphasizes the influence of different stereogenic elements on the chiroptical responses across various energy ranges with appealing 'match -mismatch' effects. Finally, we describe future prospects of helicene NHCs, particularly in the context of emerging research on cost-effective and abundant transition metals for materials science and for photocatalysis. Indeed, the inherent long-lived MLCT, excited state delocalization, structural rigidity, and intrinsic chirality of these complexes present intriguing avenues for future investigations.

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Dates et versions

hal-04762999 , version 1 (01-11-2024)

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Debsouri Kundu, Natalia Del Rio, Jeanne Crassous. Chiral Organometallic Complexes Derived from Helicenic N -Heterocyclic Carbenes (NHCs): Design, Structural Diversity, and Chiroptical and Photophysical Properties. Accounts of Chemical Research, 2024, 57 (20), pp.2941-2952. ⟨10.1021/acs.accounts.4c00275⟩. ⟨hal-04762999⟩
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