Halide Ligands Control Optical and Chiroptical Response of DNA-Stabilized Ag ₂₈ Clusters in the Near-Infrared Region: Theoretical Prediction and Experimental Confirmation

Recent experiments [Romolini; Small Structures 2025, 2500022] uncovered the crystallographic structure of a near-infrared (NIR) emitting DNA-stabilized silver nanocluster, DNA2Ag28Cl2, which has two chloridos bound to the silver core. Here, we study the role of the halido in the cluster’s photophysical properties by replacing X = Cl with X = Br, I, H2O, or OH in a computational model for density functional theory (DFT) calculations. The calculations predict a systematic red shift of the NIR absorption and enhancement of a negative circular dichroism (CD) signal in the range of 810–860 nm when Cl, Br, and I are used as halide ligands, respectively. Leaving the two halido sites empty but coordinated by water molecules blue-shifts the linear absorption and CD signal from 810 nm and dramatically switches the CD sign. The explanations for this behavior are found by a detailed analysis of the electronic structure and the impact of the X ligands to the frontier orbitals. We directly verify the DFT predictions experimentally in the case of X = Br by performing a series of experiments with a controlled Cl-to-Br exchange. These findings demonstrate the importance of the halide ligands in controlling the near-infrared optical and chiroptical response of DNA-stabilized silver nanoclusters.