One- and two-photon induced emission in heterobimetallic ZnII–SmIII and ZnII–TbIII complexes with a side-off compartmental ligand

Abstract

Heterobimetallic [Zn^IILn^III] complexes have been obtained using a compartmental Schiff-base ligand, H₂valdmpn, resulting from the 2 : 1 condensation between o-vanillin and 2,2-dimethyl-propilenediamine: [Zn(H₂O)(valdmpn)Sm(O₂NO)₃] 1, [Zn(H₂O)(valdmpn)Tb(O₂NO)₃] 2a, [Zn(H₂O)(valdmpn)Tb(O₂NO)₃]·H₂O 2b, and [Zn(H₂O)(valdmpn)Gd(O₂NO)₃]·H₂O 3. The crystal structures of 1, 2b, and 3 have been solved. Compounds 1 and 2a crystallize in a non-centrosymmetric space group (P2₁2₁2₁), being isomorphous. Crystals 2b and 3 are also isomorphous (space group P). The complex entities in the four crystals are similar and their structures consist of binuclear species with the pentacoordinated zinc(II) ion hosted into the N₂O₂ compartment and the lanthanide(III) ion in the large, open compartment, with a coordination number of 10. The photophysical properties of the four compounds have been investigated. Strong visible excited (excitation tails extend up to 420–430 nm) one photon antenna sensitization was obtained with the samarium(III) and terbium(III) derivatives. Following femtosecond Ti:Sapphire laser at λ_ex = 775 nm, both second-harmonic generation at λ_em = 775/2 nm and two-photon induced emission in the VIS range were obtained, extending thus the excitation range of these complexes from the VIS to the NIR spectral range. The two-photon induced emission and second harmonic generation effect for a samarium(III) complex are reported for the first time.