Evolution of Circularly Polarized Luminescence in Atomically Precise Silver Nanoclusters with Intrinsic Chirality

Circularly polarized luminescence (CPL) is a powerful tool to probe the chiroptical properties of molecular systems in the excited state. Here, we demonstrate the evolution of excited-state chiroptical property in silver nanoclusters (NCs) by CPL measurements. The use of bidentate thiolate ligand, 1,3-benzenedithiol (BDT), with the aid of triphenylphosphine (PPh₃), affords racemic [Ag₂₉(BDT)₁₂(PPh₃)₄]^3- NCs (Ag₂₉ NCs) with intrinsic chirality in the exterior cage composed of a silver(I)-dithiolate coordination framework, that are separable by chiral column chromatography. We have recently reported that the post-synthetic modification of negatively charged Ag₂₉ NCs with a cationic silver(I) complex on the exterior cage stabilizes a specific excited state with a triplet character, enhancing photoluminescence (PL) in the near-infrared (NIR) region. While the same modification on the separated enantiomeric NCs does not change the circular dichroism (CD) profile so much, the CPL activity is dramatically enhanced with an increase in the anisotropy factor (|g_lum| value) from <1 × 10^-3 to 6 × 10^-3, demonstrating the excited-state dependent CPL property of Ag₂₉ NCs. In combination with the picosecond PL decay study, the low-temperature CPL measurement indicates the time development of excited-state property, suggesting the possible evolution of CPL activity.