pH Guided Pathways Trigger Tailoring of Chiral Luminescence in Enantiomeric Gold Cluster Assemblies

Abstract

The modulation of chirality has been a subject of scientific research for past decades due to its broad and impactful applications in drug discovery, catalysis, and biotechnology. However, the control of chirality at the nanoscale is challenging and has recently attracted significant attention due to its implications in diverse fields ranging from medicine to catalysis, optoelectronic devices and materials science. While the ground-state chiral modulation has been a topic of investigation in various nanosystems, the manipulation of excited-state chirality remains relatively underexplored. Herein, we report a straightforward approach to modulate and enhance both the ground and excited state chiral anisotropy in a pair of gold clusters, via pH modulations. Gold cluster aggregates synthesized using cysteine as a surface ligand, facilitated the adoption of distinct structural features at different pH ranges. By systematically varying the pH across the acidic, isoelectric, and basic regions of the amino acid, the relative engagement of hydrogen bonding and two-point local dipolar interactions could be effectively altered, thereby modulating the nature of cluster aggregation and the resultant chiroptical responses. The pH driven aggregation induced enhanced emission coupled with generation and modulation of cluster assemblies exhibiting highest among the reported chiral anisotropies for monometallic clusters, emphasizes both the novelty of the approach and the potential of the nanomaterials for application in chiral light emitting devices. Moreover, the work provides fundamental insights into the mechanism of pH-dependent supramolecular assembly of molecules and materials.