Chiral cadmium–amine complexes for stimulating non-linear optical activity and photoluminescence in solids based on aurophilic stacks†

The design of high-performance optical materials can be realized using coordination polymers (CPs) often supported by non-covalent interactions, such as metallophilicity. The challenge is to control two or more optical effects, e.g., non-linear optics (NLO) and photoluminescence (PL). We present a new strategy for the combination of the NLO effect of second-harmonic generation (SHG) and the visible PL achieved by linking dicyanidoaurate(I) ions, which form luminescent metallophilic stacks, with cadmium(II) complexes bearing chiral amine ligands, used to break the crystal's symmetry. We report a family of NLO- and PL-active materials based on heterometallic Cd(II)–Au(I) coordination systems incorporating enantiopure propane-1,2-diamine (pda) ligands (1-S, 1-R), their racemate (2), and enantiopure trans-cyclopentane-1,2-diamine (cpda) ligands (3-S, 3-R). Due to acentric space groups, they exhibit the SHG signal, tunable within the range of 11–24% of the KDP reference, which was correlated with the dipole moments of Cd(II) units. They show efficient blue PL whose energy and quantum yield, the latter ranging from 0.40 to 0.83, are controlled by Cd(II) complexes affecting the Au–Au distances and vibrational modes. We prove that chiral Cd(II)–amine complexes play the role of molecular agents for the stimulation of both the NLO and PL of the materials based on aurophilic stacks.