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Keywords:

  • chromophores;
  • lanthanides;
  • luminescence;
  • polymers;
  • supramolecular chemistry

Abstract

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Flexible director: A flexible multidentate linker containing picolinate chromophores directs the selective formation of luminescent 1D lanthanide-based polymers. Partial protonation significantly decreases the preorganization of the linker, thus leading to supramolecular 1D and 2D isomers (see scheme). The lanthanide-containing 1D polymers undergo reversible structural modification in the hydration/dehydration process, which is also associated with significant differences in the luminescence emission.

Four picolinate building blocks were implemented into the multidentate linker N,N′,N′-tetrakis[(6-carboxypyridin-2-yl)methyl]butylenediamine (H4tpabn) with a linear flexible spacer to promote the assembly of lanthanide-based 1D coordination polymers. The role of the linker in directing the geometry of the final assembly is evidenced by the different results obtained in the presence of Htpabn3− and tpabn4− ions. The tpabn4− ion leads to the desired 1D polymer {[Nd(tpabn)]H3O⋅6 H2O} (12). The Htpabn3− ion leads to the assembly of TbIII and ErIII ions into 1D zigzag chains of the general formula {[M(Htpabn)]⋅x H2O} (M=Tb, x=14 (1); M=Tb, x=8 (11); M=Er, x=14 (2); M=Er, x=5.5 (4)), a 2D network is formed by the EuIII ion (i.e., {[Eu(Htpabn)]⋅10 H2O} (7)), and both supramolecular isomers (1D and 2D) are obtained by the TbIII ion. The high flexibility of the polymeric chains results in a dynamic behavior with a solvent-induced reversible structural transition. The TbIII- and EuIII-containing polymers display high-luminescence quantum yields (38 and 18 %, respectively). A sizeable near-IR luminescence emission is observed for the ErIII- and NdIII-containing polymers when lattice water molecules are removed.