Single-Atom Tunning Visible-Near-Infrared CPL in Chiral Metal Clusters

Abstract

Circularly polarized luminescence (CPL)-active nanoclusters hold great promise for advanced photonic applications, yet the improvement of the |g_lum| has always been the core challenge in this field for a long time. Herein, we report the enantiomeric pairs of homometallic cationic (R/S)-[Ag₂₁(S₂PO₂C₁₇H₁₄)₁₂]⁺ (R/S-Ag₂₁) and heterometallic neutral (R/S)-[PtAg₂₀(S₂PO₂C₁₇H₁₄)₁₂] (R/S-PtAg₂₀) clusters stabilized by a bis-thiophosphinate spiro ligand and featuring eight free electrons. R/S-Ag₂₁ exhibits a single emission with a |g_lum| value of 4.7 × 10⁻⁴, whereas R/S-PtAg₂₀ with only one atom changed exhibits visible-near-infrared (NIR) dual emission CPL behavior, with a visible-light emission |g_lum| value of 6.4 × 10⁻⁴ and an NIR emission |g_lum| value of 1.3 × 10⁻²—among the highest reported for metal clusters. Research has revealed that the luminescence of R/S-PtAg₂₀ originates from two independent triplet excited states: a core-based charge transfer (CT) state and a ligand-to-core CT state, which are bridged by a direct CT process mediated by ligand vibrations. The high |g_lum| value of R/S-PtAg₂₀ in the NIR region stems from the strong correlation between its electronic cloud and the peripheral chiral ligands. Furthermore, guest-induced modulation of ligand rigidity enables tunable emission modes—visible-only, NIR-only, or dual-visible-NIR. This work presents a novel strategy for constructing DECPL-active metal clusters, offering fundamental insights into the design principles governing CPL efficiency and paving the way for multifunctional photonic systems, such as optical encryption.

Keywords

circularly polarized luminescence / metal cluster / chirality

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