Luminescence tribochromism and bright emission in gold(I) thiouracilate complexes

New dinuclear Au(I) complexes containing bridging thiouracilate and bis(diphenylphosphino)methane ligands have been synthesized and characterized structurally and spectroscopically. The compounds exhibit a unique behavior of solid-state luminescence tribochromism in which photoemission turns on upon gentle grinding of the sample and a sensitivity to pH in fluid solution. The emissive form in the solid state exhibits a bright blue or cyan emission upon irradiating at 375 nm. Structural studies show that the nonemissive form of the complexes has an extended helical ...Au...Au...Au... structure in the solid with weak aurophilic interactions, whereas the blue emissive form has a strong intermolecular aurophilic interaction in the solid that leads to an arrangement of dimers of dinuclear (Au2) complexes. Interconversion between the two forms can be carried out by either recrystallization for solid-state samples or by exposure to vapors of volatile acid or base for fluid solutions of the complexes.