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

It is challenging to attain strong near-infrared (NIR) emissive gold nanoclusters. Here we show a rod-shaped cluster with the composition of Au(p-MBT)(Hdppa) (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) Au kernel built from two interpenetrating bicapped cuboctahedral Au 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 [Au(m-MBT)(Hdppa)]SOCF (2, m-MBT is 3-methylbenzenethiolate) with a similar composition and 60-fold of AuS(S‑t‑Bu) with a similar structure. time-dependent DFT(TDDFT)calculations reveal that the luminescence of 1 is associated with the Au 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) 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 rather than the inhibition of k. This work demonstrates that the metal kernel and the surface structure are both very important for cluster-based NIR luminescence materials.