Interplay of kernel shape and surface structure for NIR luminescence in atomically precise gold nanorods

Abstract

It is challenging to attain strong near-infrared (NIR) emissive gold nanoclusters. Here we show a rod-shaped cluster with the composition of [Au₂₈(p-MBT)₁₄(Hdppa)₃](SO₃CF₃)₂ (1 for short, Hdppa is N,N-bis(diphenylphosphino)amine, p-MBT is 4-methylbenzenethiolate) has been synthesized. Single crystal X-ray structural analysis reveals that it has a rod-like face-centered cubic (fcc) Au₂₂ kernel built from two interpenetrating bicapped cuboctahedral Au₁₅ units. 1 features NIR luminescence with an emission maximum at 920 nm, and the photoluminescence quantum yield (PLQY) is 12%, which is 30-fold of [Au₂₁(m-MBT)₁₂(Hdppa)₂]SO₃CF₃ (2, m-MBT is 3-methylbenzenethiolate) with a similar composition and 60-fold of Au₃₀S(S‑t‑Bu)₁₈ with a similar structure. time-dependent DFT(TDDFT)calculations reveal that the luminescence of 1 is associated with the Au₂₂ kernel. The small Stokes shift of 1 indicates that it has a very small excited state structural distortion, leading to high radiative decay rate (k_r) probability. The emission of cluster 1 is a mixture of phosphorescence and thermally activated delayed fluorescence(TADF), and the enhancement of the NIR emission is mainly due to the promotion of k_r rather than the inhibition of k_nr. This work demonstrates that the metal kernel and the surface structure are both very important for cluster-based NIR luminescence materials.

Gold nanoclusters with strong emissions in the near-infrared are challenging to attain. Here, the authors show that for rod-shaped nanoclusters, both the shape of the kernel and the rigid surface structure are important to increase the NIR emissions.