Quinoxaline sensitised lanthanide ion luminescence: Syntheses, spectroscopy and X-ray crystal structure of Na{1,4,7-tris[(N-diethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane-10-(2-methylquinoxaline)}I3 C7H8

The synthesis of a quinoxaline-appended aza-macrocyclic ligand together with corresponding LnIII complexes are described. The luminescence properties of the complexes show that the quinoxaline unit sensitises both visible (EuIII) and near-IR (NdIII and YbIII) emitting lanthanide ions. UV–Vis absorption and time-resolved photophysical studies together with X-ray structural data suggest that as well as contributing chromophorically, the quinoxaline moiety generally participates in the first coordination sphere of LnIII. The luminescent pH response of the EuIII complex is also reported. The form of the steady state spectrum changes profoundly in the pH range 2–12, implying a change in the coordination environment, which was confirmed with time-resolved lifetime measurements that suggest an increase in europium inner sphere hydration at acidic pH.

Graphical abstractThe syntheses and photophysical attributes of a series of quinoxaline-functionalised lanthanide complexes based on a tetra-aza macrocyclic architecture are described. Irradiation of the quinoxaline chromophore results in sensitised lanthanide emission from NdIII, EuIII and YbIII. The coordinative ability and basicity of the quinoxaline unit were also exploited in the luminescent, pH responsive EuIII complex.Figure optionsDownload full-size imageDownload as PowerPoint slide