Luminescence Thermochromism of Gold(I) Phosphane-Iodide Complexes: A Rule or an Exception?

A series of gold(I) iodide complexes 1-11 have been prepared from di-, tri-, and tetraphosphane ligands. Crystallographic studies reveal that the di- (1-7) and tetrametallic (11) compounds feature linearly coordinated gold(I) ions with short aurophilic contacts. Their luminescence behavior is determined by the combined influence of the phosphane properties, metal-metal interaction, and intermolecular lattice-defined interactions. The proposed variable contribution of 3 (X+M)-centered (X=halogen; M=metal) and 3 XLCT (halogen to ligand charge transfer) electronic transitions into the lowest lying excited state, which is influenced by supramolecular packing, is presumably responsible for the alteration of room-temperature emission color from green (λ=545 nm, for 11) to near-IR (λ=698 nm, for 2). Dinuclear compounds 6 and 7 exhibit distinct luminescence thermochromism with a blueshift up to 5750 cm-1 upon cooling. Such dramatic change of emission energy is assigned to the presence of two coupled triplet excited states of 3 ππ* and 3 (X+M)C/3 XLCT nature, the presence of which depends on both molecular structure and the crystal lattice arrangement.