Significant Enhancement of Absorption and Luminescence Dissymmetry Factors in the Far-Red Region: A Zinc(II) Homoleptic Helicate Formed by a Pair of Achiral Dipyrromethene Ligands

A homoleptic zinc(II) helicate organized by a pair of achiral dipyrromethene ligands through zinc(II) coordination was synthesized to evaluate the chiroptical properties. This zinc complex showed strong exciton-coupled chiroptical responses from the helical configuration with a large absorption dissymmetry factor |g(abs)| (up to 0.20). More importantly, intense polarized luminescence in the far-red region (700-850 nm) with a fluorescence quantum yield phi(FL) of 0.23 was observed for this helicate with a dissymmetry factor |g(lum)| of 0.022, the largest value among rare-earth- and precious-metal-free small molecules. These unprecedentedly large g values were supported by theoretical calculations.