Crowded bis-(M-salphen) [M = Pt(II), Zn(II)] coordination architectures: luminescent properties and ion-selective responses.

For binuclear luminescent host systems, cooperativity between metal-organic moieties becomes feasible with regards to photophysical properties and sensing behavior. A new class of conformationally rigid binuclear platinum(II) and zinc(II) complexes bearing tetradentate aromatic Schiff base (salphen) ligands with limited rotational freedom has been prepared and characterized, and the molecular structure of a (Pt-salphen)2 derivative has been determined by X-ray crystallography. Their UV-vis absorption and emission properties have been investigated and are tentatively ascribed to different excited states depending on the metal and the extent of intramolecular π-stacking interactions. Colorimetric and phosphorescent responses by the bis-Pt(II) complexes in the presence of selected metal ions have been observed. The nature of the host-guest interactions has been examined by quantitative binding studies, mass spectrometry and DFT calculations, and through comparisons with control complexes.