Post-synthetic Bromination of a Dinuclear Aluminum Helicate and Its Chiroptical Properties

Dinuclear aluminum-based triple-stranded helicates were functionalized through post-synthetic bromination with N-bromosuccinimide, enabling direct modification of a pre-assembled helical framework. By controlling of the reagent equivalents, mono- and octadecabrominated derivatives were selectively obtained while the helical structure was preserved. Increasing the degree of bromination induced red shifts in both the absorption and emission wavelength, reflecting systematic modulation of the electronic structures. In addition, the complexes exhibit large Stokes shifts, and optical resolution of these complexes yields enantiomers exhibiting mirror-image circular dichroism and circularly polarized luminescence.