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Published on: June 23, 2023
Metal-Assisted Synthesis of Extended Polyaromatic Nitrogen-Rich Ligands for Tunable Sensitization of Eu(III)
Giau Le-Hoang1, Laure Guénée2, Melanda Bertrand-Avebe1
1Department of Inorganic and Analytical Chemistry, University of Geneva, 30 quai E. Ansermet, CH-1211 Geneva, Switzerland.
Abstract:
We report the metal-assisted synthesis of oligomeric nitrogen-rich DiL1 and PoL1 sensitizers from the monomer L1 via acyclic diene metathesis (ADMET) polymerization for the tuning of the photoluminescence properties of europium-containing complexes by ligand design. The binding of [Eu(hfac)3] cargoes (H-hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) to monomer L1 to give [L1Eu(hfac)3] during metathesis appeared to be essential (i) for protecting the Grubbs ruthenium catalyst to interact with the nitrogen atoms of L1 and (ii) to drive the Ru-catalyzed ADMET reaction toward dimeric {DiL1[Eu(hfac)3]2} and polymeric {PoL1[Eu(hfac)3]} assemblies. Compared with the monomeric tridentate L1-L4 ligands, significant electronic delocalization occurs through the π-conjugated benzimidazole-CH═CH-benzimidazole skeletons in the dimer DiL1 and polymers PoL1, which results in a stepwise red-shift of the excited levels in these extended polyaromatic ligands. As a consequence, the sensitization of bound [Eu(hfac)3] units reveals a decrease of the photoluminescence quantum yields along the [L4Eu(hfac)3] > [L3Eu(hfac)3] > [L2Eu(hfac)3] ≈ [L1Eu(hfac)3] > {DiL1[Eu(hfac)3]2} > {PoL1[Eu(hfac)3]18} series due to unfavorable europium-to-ligand back energy transfers.
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