Emission Properties of [Au(CN)₂]^- Oligomers in Crystals with One-Dimensional Au Chain Structures

The crystal structures of (Me₄N)₃[Au(CN)₂]₂Cl (Me₄N: tetra-methylammonium, 1) and Et₄N[Au(CN)₂] (Et₄N: tetra-ethylammonium, 2) were found to include 1-dimensional Au chain structures, where the Au···Au distance is as short as 3.3 Å in 1 and 3.6 Å in 2. Because the structures of the ground state oligomers have linear staggered structures, the photoexcited oligomers generated in these crystals are also expected to have linear staggered structures. The crystals exhibit emission, in which the dominant emission bands are located at 430 nm in 1 and 400 nm in 2 at 77 K with emission quantum yields of unity. These emission bands at 77 K were assignable to the phosphorescence of the tetramer and trimer of linear-staggered structures because they resemble the phosphorescence of the trimer and tetramer in aqueous solutions. The radiative lifetimes of the T₁ trimer and T₁ tetramer were estimated as 0.9 and 1.6 μs, respectively, from their quantum yields and lifetimes. The emission lifetime of 2 was observed in the temperature region of 4-110 K to estimate the zero-field splitting of the lowest triplet state of the trimer as 36 cm^-1 (E_I-II) and 64 cm^-1 (E_I-III) and the radiative rate constants of the three states as 1.43 × 10³ s^-1 (k_I), 2.0 × 10⁴ s^-1 (k_II), 4.8 × 10⁶ s^-1 (k_III).