Effects of Heavier Congeners on the Structural and Photophysical Properties of Visible-Light-Absorbing Dinuclear Complexes of Group-12 Elements

Unlike most d-block metal complexes, group-12 metal complexes exhibit a lack of visible light absorption involving atomic orbital of metal center, despite the growing demand for visible light-driven photofunctional materials. To overcome this limitation, we previously developed a dinuclear Zn(II) complex that absorbs visible light through an empty sigma orbital formed between two proximal Zn atoms and exhibits dual emission at 77 K. However, the roles of the central metal atom in influencing the structural and photophysical properties were not fully investigated. In this study, we synthesized a dinuclear Cd(II) complex, structurally analogous to the Zn(II) complex, to investigate the effects of the central metal atoms on these properties. Structural analyses revealed that both complexes are highly similar, with slightly elongated Cd-Cd distances because of Cd's larger van der Waals radius. Theoretical calculations indicated attractive intermetallic interactions between the central metal atoms in both complexes. Although both complexes displayed negligibly different visible light absorptions, the Cd(II) complex displayed a much higher intersystem crossing rate than the Zn(II) complex, generating distinctly different overall emission profiles. These findings emphasize the crucial roles of the central metal atoms in influencing the structural and photophysical behaviors of dinuclear complexes, providing deeper insights for designing group-12-element-based materials.