All‐alkynyl Protected Rod‐Shaped Au9(AgCu)126 Nanocluster with Remarkable Photothermal Conversion

The synthesis of large-size alloy nanoclusters (~2 nm) is still challenging. An all-alkynyl protected [Au9Ag126-xCux(PhC≡C)68(BF4)]4+ (x=0 ~ 20) (1) trimetallic nanocluster has been synthesized and structure determined by SCXRD. Cluster 1 contains a concentric metal kernel in the manner of shell-by-shell arrangements Au3Ag34@Au6Ag64@(AgCu)28 protected by 68 PhC≡C ligands with 15 distinct alkynyl-metal binding configurations. Theoretic calculation reveals that the 1 features a HOMO-LUMO energy gap of 0.29 eV. This suggests that 1 is situated at the boundary of the transition from a molecular to a metallic state. Remarkably, compared to other reported Au/Ag/Cu/Pd based nanoclusters, 1 exhibit significantly enhanced photothermal conversion capability. A substantial temperature rise of ~ 51.5 °C within 5 min (λex = 660 nm, 0.5 W/cm2) and a record high photothermal conversion efficiency of 84.7% at 12 μM in N, N-dimethylformamide (DMF) were observed.Time-resolved transient absorption(TA) spectroscopy reveals that the electron-phonon coupling (τe-ph) of excited 1 occurs on the femtosecond timescale, resulting in an ultrafast electronic relaxation process and excellent photothermal performance. Cluster 1, when employed as a photothermal material, shows promise in biothermal therapy, photothermal catalysis, and photothermal imaging.