Photoluminescence of Ag(i) complexes with a square-planar coordination geometry: the first observation

The first observation of luminescence from Ag(i) complexes with a square-planar geometry of the metal is reported. [Ag(Py3PO)(2)]ClO4 and [Ag(Py3PO)(2)]OTf - first examples of the emissive square-planar Ag(i) complexes - have been synthesized by the reaction of tris(2-pyridyl)phosphine oxide (Py3PO) with Ag(i) salts. Both complexes exhibit pronounced photoluminescence in the solid state at ambient temperature with nano- and microsecond lifetime components. Remarkably, the luminescence of the complexes has a reversible thermochromic behavior, changing their emission color from yellow (lambda emmax approximate to 585 nm) at room temperature to red-orange (lambda emmax = 620 nm) at 77 K. The spectroscopic and computational results reveal that the emission of the title compounds can be assigned to the (MLCT)-M-3 phosphorescence with admixture of the (MLCT)-M-1 fluorescence.