Solvent Dependence of [Au11(BINAP)4X2: X = Cl or Br]+ Cluster Electronic and Optical Properties.

Complex cluster-solvent interactions were investigated for 11-metal-atom monolayer-protected gold nanoclusters dispersed in a variety of solvents. Ultraviolet-visible (UV-vis), photoluminescence, and femtosecond transient absorption (fs-TA) spectroscopies were employed to examine the effect of solvent identity on the photophysical properties of [Au₁₁(BINAP)₄X₂]⁺, where X represents Cl or Br. UV-vis absorption spectra showed a narrowing of spectral peaks when the clusters were dispersed in protic solvents, indicating increased cluster rigidity in these solvents. Photoluminescence studies revealed that emission profiles can be tuned by modulating the cluster-solvent interaction. fs-TA experiments further supported the assignment of distinct radiative decay pathways based on the strength of the cluster-solvent interactions and also demonstrated that ethanol binding to [Au₁₁(BINAP)₄X₂]⁺ clusters is more thermodynamically stable than butanol binding. ¹H nuclear magnetic resonance spectroscopy provided evidence for cluster-solvent hydrogen bonding between [Au₁₁(BINAP)₄Cl₂]⁺ and ethanol in the form of downfield-shifted and exchange-broadened peaks. These data indicate that cluster-solvent hydrogen bonds can be tuned, emphasizing the important role of the solvation shell in determining the electronic and optical properties of atomically precise nanoclusters.