Sensitized Lanthanide-Ion Luminescence with Aryl-Substituted N-(2-Nitrophenyl)acetamide-Derived Chromophores

The syntheses of the two tetraazamacrocyclic ligands L1 and L2 bearing a [(methoxy-2-nitrophenyl)amino]carbonyl chromophore, i.e., an N-(methoxy-2-nitrophenyl)acetamide moiety, together with their corresponding lanthanide-ion complexes are described. A combined spectroscopic (UV/VIS, H-1-NMR), structural (X-ray), and theoretical (DFT) investigation revealed that the absorption properties of the chromophores were dictated by the extent of electronic delocalisation, which in turn was determined by the position of the MeO substituent at the aromatic ring. X-Ray crystallographic studies showed that when attached to the macrocycle, both isomeric forms of the N-(methoxy-2-nitrophenyl)acetamide unit can participate in coordination, via the C=O, to an encapsulated potassium cation. Luminescence measurements confirmed that such a binding mode also exists in solution for the corresponding lanthanide complexes (q ca. <= 1), with the para-MeO derivative allowing longer wavelength sensitization (lambda(ex) 330 nm).