Theoretical Analysis of the Electronic Structure and Optical Properties of DNA-Stabilized Silver Cluster Ag16Cl2 in Aqueous Solvent

DNA-stabilized silver nanoclusters with 10 to 30 silver atoms are by construction ideal candidates for biocompatible bright fluorescent emitters but their electronic structure is not well understood. Here, using density functional theory (DFT), we analyze the ground-state electronic structure and optical absorption of a bright NIR-emitting cluster Ag16Cl2 which is stabilized by two DNA strands of 9-base sequence 5’-CACCTAGCG-3’ and whose atomic structure was very recently confirmed to have two chlorides bound to the silver core. We are able to (i) unambiguously assign the charge of this cluster in aqueous solvent, (ii) analyze the details of silver–DNA interactions and their effect on the cluster charge, (iii) analyze the character of low-energy optical absorption peaks and the involved electron orbitals and make a first assessment on circular dichroism, and (iv) evaluate the suitability of various DFT exchange-correlation functionals via benchmarking to experimental optical data. This work lays out a baseline for all future theoretical work to understand the electronic, chiroptical and fluorescence properties of these fascinating bio-compatible nanostructures.