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 3XLCT (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 3ππ* and 3(X+M)C/3XLCT nature, the presence of which depends on both molecular structure and the crystal lattice arrangement. Control the glow: A delicate interplay of intramolecular features and subtle intermolecular interactions is capable of producing gold(I) complexes with distinct thermochromic luminescence (see figure), which results from reversible switching between two coupled excited states.