Controlling Circularly Polarized Luminescence through Sequential Ligand Functionalization of Aluminum Oxo Clusters

Abstract

Chiral metal-organic clusters (cMOCs) are characterized by diverse chiral origins, tunable luminescence, and multifunctionality. Among them, chiral aluminum oxo clusters (AlOCs) exhibit unique advantages in terms of resource sustainability and environmental friendliness compared to other cluster materials. Nevertheless, the simultaneous achievement of precise enantiomeric control and optical response within AlOCs remains a critical challenge to be addressed in the field. Herein, we achieve precise control over the transition from chirality to circularly polarized luminescence properties in AlOCs by leveraging their highly flexible and modifiable coordination surfaces through a stepwise ligand functionalization strategy. We employed the Al₂ cluster as a platform with programmable surface coordination sites and introduced classical chiral L/D-valine molecules. We successfully constructed four pairs of alcohol-coordinated pure chiral enantiomers (AlOC-189-L/D-MeOH, EtOH, PrOH, and PDO). Absolute helical structures can be identified in the supramolecular architectures of clusters, achieving unambiguous chirality transfer from chiral ligands to chiral clusters and further to absolute helical superstructures. Hierarchical ligand modification, endowed with a top-down design paradigm, offers a rational and feasible route to cluster functionalization. Based on the excellent replaceability of the Al₂ cluster's surface coordination sites, we achieved chiral-luminescent bifunctional coupling by partially substituting the chiral ligands with π-conjugated naphthyl-based luminophores (HNA/HNN), yielding two new classes of enantiomers (AlOC-190-L/D-HNA and AlOC-190-L/D-HNN) exhibiting bright yellow-green photoluminescence (PL). DFT calculations reveal that this is attributed to a ligand-to-ligand charge transfer (LLCT) luminescence mechanism. Notably, AlOC-190-L/D-HNN exhibited promising circularly polarized luminescence (CPL) activity via the synergy between chiral induction from L/D-valine ligands and intermolecular charge transfer of the HNN ligands. This work not only highlights the highly designable coordination chemistry of AlOC—enabling on-demand integration of specific functionalities through modular ligand substitution—but also establishes a novel "ligand editing" paradigm for developing multifunctional chiral optical materials.

Keywords

Aluminum oxo cluster / Stepwise ligand modification / Chiral clusters / Chirality transfer / Circularly polarized luminescence

RIGHTS & PERMISSIONS

2025 SIOC, CAS, Shanghai, & WILEY-VCH GmbH