Phosphorescent molecular tweezers based on alkynylplatinum(II) terpyridine system: turning on of NIR emission via heterologous Pt•••M interactions (M = PtII, PdII, AuIII and AuI)

A novel molecular tweezers-type complex 1, based on a phosphorescent cationic alkynylplatinum(II) terpyridine building block, has been synthesized and characterized by NMR, mass spectroscopy, elemental analysis and X-ray diffraction study. Host-guest chemistry of the host complex 1 and various guest metal complexes with different ligands, charges and/or metal centres has been investigated. Various metal complexes including the negatively charged platinum complexes can interact with 1 in a 1 : 1 manner, which is in contrast to the commonly observed formation of insoluble platinum(II) double salts in a one-dimensional infinite chain such as the Magnus's green salt. Upon addition of guest molecules to 1 in CH2Cl2 solution, spectroscopic changes with new absorptions and emissions in the lower-energy region were observed as a result of significant metal-metal, pi-pi, and electrostatic interactions. H-1 NMR titration and 2D NMR studies suggest that the host-guest interaction is predominantly in the sandwiched association mode of the molecular tweezers.