Electronegativity of the Substituent on Surface Motifs Influences the Ultrafast Relaxation Dynamics of Ag44(SR)304-Nanoclusters

This work presents the influence of the substituent groups of surface staple motifs on the ultrafast relaxation dynamics of atomically precise Ag44(SR)304- nanoclusters (NCs). A series of Ag44 NCs, with Ag32 core and Ag12(SR)30 staple motifs, have been studied, where thiophenol (TP), 4-fluorothiophenol (FTP), and 4-chlorothiophenol (CTP) are chosen as protecting ligands. This work reveals that the electronegativity and polarization of the surface ligand control the electron-phonon interaction, which ultimately influences the population transfer from the core state to the surface state of the Ag44 NCs upon photoexcitation. Global analysis of the transient absorption spectroscopic data reveals the slower relaxation from the core state to the surface state, depending on electronegativity. The ligand-protected Ag44 NCs show a fast internal conversion (similar to 2 ps), core-to-surface relaxation (900-1000 ps), and slower electron-hole recombination (>8 ns). The analysis of Ag44 NCs and the closely bare system Ag32 NCs reveals the impact of surface states on this three-state relaxation process. This study provides insights into the origin of the excited-state decay times and is expected to stimulate future work on Ag NCs.

Automated summary

This work investigates the impact of substituent groups on the relaxation dynamics of atomically precise Ag44(SR)304- nanoclusters. The electronegativity and polarization of the surface ligands are found to control the electron-phonon interaction, affecting the population transfer within the nanoclusters upon photoexcitation. Transient absorption spectroscopic data analysis reveals a slower relaxation process from the core state to the surface state, depending on the electronegativity. The ligand-protected Ag44 nanoclusters exhibit fast internal conversion, core-to-surface relaxation, and slower electron-hole recombination.