Electronic relaxation dynamics in [Au25(SR)18]-1 (R = CH3, C2H5, C3H7, MPA, PET) thiolate-protected nanoclusters

We investigate the excited electron dynamics in [Au-25(SR)(18)](-1) (R = CH3, C2H5, C3H7, MPA, PET) [MPA = mercaptopropanoic acid, PET = phenylethylthiol] nanoparticles to understand how different ligands affect the excited state dynamics in this system. The population dynamics of the core and higher excited states lying in the energy range 0.00-2.20 eV are studied using a surface hopping method with decoherence correction in a real-time DFT approach. All of the ligated clusters follow a similar trend in decay for the core states (S-1-S-6). The observed time constants are on the picosecond time scale (2-19 ps), which agrees with the experimental time scale, and this study confirms that the time constants observed experimentally could originate from core-to-core transitions and not from core-to-semiring transitions. In the presence of higher excited states, R = H, CH3, C2H5, C3H7, and PET demonstrate similar relaxations trends whereas R = MPA shows slightly different relaxation of the core states due to a smaller gap between the LUMO+1 and LUMO+2 gap in its electronic structure. The S-1 (HOMO -> LUMO) state gives the slowest decay in all ligated clusters, while S-7 has a relatively long decay. Furthermore, separate electron and hole relaxations were performed on the [Au-25(SCH3)(18)](-1) nanocluster to understand how independent electron and hole relaxations contribute to the overall relaxation dynamics.