Décembre 2019. Publication de Narcis Avarvari dans European Journal of Inorganic Chemistry.

 

Helicene Bis(pyrazol-1-yl)pyridine Ligands for Luminescent
Transition-Metal Complexes.

Alexandre Abhervé, Kévin Martin, Andreas Hauser, and Narcis Avarvari.


Abstract: We describe herein the synthesis of 2,6-bis(pyrazol-1-yl)pyridine (1-bpp) ligands substituted by helicene units in the 4-position of the pyridine ring. The two-step procedure afforded the molecules bpp[n]helicene (n = 4, 5 and 6) and methyl-bpp[4]helicene, abbreviated as 4, 5, 6 and 4m respectively, with overall good yields. This series of ligands shows fluorescence in the violet region, with a red shift of the emission when increasing the number of aromatic rings in the helicene unit. The tridentate fluorophores have been reacted with Re(CO)5Cl and [Ru(terpy)Cl3] to prepare a series of transition metal complexes formulated as [ReI(n)(CO)3Cl] (n = 4 and 5) and [RuII(n)(terpy)](PF6)2 (n = 4, 4m, 5 and 6). The compounds [ReI(4)(CO)3Cl]·(CH2Cl2)0.5(H2O) and [RuII(4m)(terpy)](PF6)2 crystallized in the centrosymmetric space groups P21/n and P1¯ respectively, and thus present both M and P helicene units in their crystal structures. The absorption and emission properties of the complexes have been studied. All complexes show luminescence at 77 K in frozen DCM solution. The tricarbonyl complex [ReI(5)(CO)3Cl] shows a strong emission band with two peaks at 540 nm and 580 nm, which could be attributed to ligand-localized π–π* phosphorescence due to the extended π system of the ligand. The heteroleptic RuII complexes show
emission bands above 600 nm attributed to the terpyridinebased 3MLCT state.

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