Electronegativity of the Substituent on Surface Motifs Influences the Ultrafast Relaxation Dynamics of Ag<sub>44</sub>(SR)<sub>30</sub><sup>4–</sup> Nanoclusters
Sarita Kolay, Subarna Maity, Sikta Chakraborty, Srijon Ghosh, Amitava Patra
Abstract
This work presents the influence of the substituent groups of surface staple motifs on the ultrafast relaxation dynamics of atomically precise Ag 44 (SR) 30 4– nanoclusters (NCs). A series of Ag 44 NCs, with Ag 32 core and Ag 12 (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 Ag 44 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 Ag 44 NCs show a fast internal conversion (∼2 ps), core-to-surface relaxation (900–1000 ps), and slower electron–hole recombination (>8 ns). The analysis of Ag 44 NCs and the closely bare system Ag 32 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.