Two-way vapochromism of a luminescent platinum(ii) complex with phosphonic-acid-functionalized bipyridine ligand.

A luminescent Pt(ii) complex [Pt(CN) ₂ (H ₄ dpbpy)] (1P; H ₄ dpbpy = 2,2'-bipyridine-4,4'-diphosphonic acid) bearing a phosphonic-acid-functionalized bipyridine ligand was successfully synthesized and its unique two-way vapochromic behaviour investigated. X-ray structure analyses of both the anhydrous 1P and penta-hydrated 1P·5H2O phases clearly reveal the activation of intermolecular PtPt interactions through the adsorption of water vapour. Emission spectroscopy reveals that the penta-hydrated 1P·5H2O complex exhibits an orange emission at 585 nm that shifts in two directions, to a blue-green emission at 469 nm by drying at 100 °C or to a red emission at 701 nm by drying under vacuum at room temperature. Thermogravimetric analyses and powder X-ray diffraction studies clearly reveal that anhydrous 1P, with negligible intermolecular PtPt interactions, is formed by drying at 100 °C whereas the monohydrate 1P·H2O phase, with effective PtPt interactions, is formed by drying under vacuum.