A [Cyclentetrakis(methylene)]tetrakis[2-hydroxybenzamide] Ligand That Complexes and Sensitizes Lanthanide(III) Ions

The synthesis of the cyclen derivative H4L1⋅2 HBr containing four 2‐hydroxybenzamide groups is described. The spectroscopic properties of the LnIII conplexes of L1 (Ln=Gd, Tb, Yb, and Eu) reveal changes of the UV/VIS‐absorption, circular‐dichroism‐absorption, luminescence, and circularly polarized luminescence spectra. It is shown that at least two metal‐complex species are present in solution, whose relative amounts are pH dependent. At pH>8.0, an intense long‐lived emission is observed (for [TbL1] and [YbL1]), while at pH