Axially chiral BINOL-derived Schiff-base Zn(II) complexes: ligand-controlled one-dimensional structures and chiroptical properties.

The photophysical and chiroptical properties of chiral emissive molecules can be influenced by both intrinsic molecular chirality and molecular organization, although their respective contributions remain insufficiently understood. In this study, we synthesized enantiomers of two Zn(II) complexes with different coordination environments to investigate how the ligand structure affects supramolecular organization and emission properties in axially chiral BINOL-derived Schiff-base Zn(II) complexes. The Schiff-base ligands were prepared by the condensation of a BINOL-derived aldehyde with amine compounds, followed by complexation with zinc(II) acetate. Single-crystal X-ray diffraction analysis revealed that the complex (R)/(S)-Zn1 forms an acetate-bridged one-dimensional coordination polymer, in which mononuclear Zn(II) units are linked through bridging acetate ligands. In contrast, the complex (R)/(S)-Zn2 adopts one-dimensional stacked columns extending along the b-axis, stabilized by π-π and CH-π interactions between the binaphthyl moieties. These results demonstrate that a subtle difference in the ligand structure induces distinct one-dimensional structural motifs through coordination bonding or intermolecular interactions. Both complexes exhibit fluorescence in solution and in the solid state, and their chiroptical properties were evaluated by circular dichroism (CD) and circularly polarized luminescence (CPL) measurements. For each enantiomer, the CPL sign and the magnitude of the dissymmetry factor remained comparable between the solution and solid states, with |glum| values on the order of 10-3. This study demonstrates that ligand design controls the mode of one-dimensional organization and modulates the emission properties, while the CPL response primarily reflects the intrinsic axial chirality of the BINOL-based Zn(II) complexes.