Reddy et al. performed calculations of equilibrium geometries, binding energies, ionization potentials, and magnetic

Understanding fundamental behavior of luminescent nanomaterials upon photoexcitation is necessary to expand photocatalytic and biological imaging applications. Despite the significant amount of experimental work into the luminescence of Au25(SR)18(-) clusters, the origin of photoluminescence in these clusters still remains unclear. In this study, the geometric and electronic structural changes of the Au25(SR)18(-) (R = H, CH3, CH2CH3, CH2CH2CH3) nanoclusters upon photoexcitation are discussed using time-dependent density functional theory (TD-DFT) methods. Geometric relaxations in the optimized excited states of up to 0.33 Å impart remarkable effects on the energy levels of the frontier orbitals of Au25(SR)18(-) nanoclusters. This gives rise to a Stokes shift of 0.49 eV for Au25(SH)18(-) in agreement with experiments. Even larger Stokes shifts are predicted for longer ligands. Vibrational frequencies in the 75-80 cm(-1) range are calculated for the nuclear motion involved in the excited-state nuclear relaxation; this value is in excellent agreement with vibrational beating observed in time-resolved spectroscopy experiments. Several excited states around 0.8, 1.15, and 1.25 eV are calculated for the Au25(SH)18(-) nanocluster. Considering the typical underestimation of DFT excitation energies, these states are likely responsible for the emission observed experimentally in the 1.15-1.55 eV range. All excited states arise from core-based orbitals; charge-transfer states or other "semi-ring" or ligand-based states are not implicated.

Ligand-stabilized gold and silver nanoparticles are of tremendous current interest in sensing, catalysis, and energy applications. Experimental and theoretical studies have closely interacted to elucidate properties such as the geometric and electronic structures of these fascinating systems. In this review, the interplay between theory and experiment is described; areas such as optical absorption and doping, where the theory-experiment connections are well established, are discussed in detail; and the current status of these connections in newer fields of study, such as luminescence, transient absorption, and the effects of solvent and the surrounding environment, are highlighted. Close communication between theory and experiment has been extremely valuable for developing an understanding of these nanocluster systems in the past decade and will undoubtedly continue to play a major role in future years.

The [Au25(SR)18]− and [Au13(dppe)5Cl2]3+ [dppe = 1,2-bis­(diphenylphosphino)­ethane] nanoclusters both possess a 13-atom icosahedral core with 8 delocalized superatomic electrons (8e), but their emission properties and time-resolved electron dynamics differ significantly. In this work, experimental photoluminescence and photoluminescence decay measurements are combined with time-dependent density functional theory calculations of radiative and nonradiative decay properties and lifetimes to elucidate the similarities and differences in the emission of these two nanoclusters with similar cores. In this work, the photodynamic properties of [Au13(dppe)5Cl2]3+ are elucidated theoretically for the first time. [Au13(dppe)5Cl2]3+ exhibits a single strong emission peak compared to the weaker bimodal luminescence of [Au25(SR)18]− (modeled here as [Au25(SH)18]−). The strongly emissive state is found to arise from deexcitation out of the S1 state, similar to what is seen for [Au25(SH)18]−. Both theory and experiment exhibit microsecond lifetimes for this state. Transient absorption measurements and theoretical calculations demonstrate that the excited-state lifetimes for higher excited states are typically less than 1 ps. The decay times for the higher excited states of [Au13(dppe)5Cl2]3+ and its model compound [Au13(pe)5Cl2]3+ [pe = 1,2-bis­(phosphino)­ethane] are observed to be shorter than the lifetimes of the corresponding states of [Au25(SR)18]−; this occurs because the energy gap separating degenerate sets of unoccupied orbitals is only ∼0.2 eV in [Au13(dppe)5Cl2]3+ compared to a ∼0.6 eV energy gap in [Au25(SH)18]−.

A ligand exchange strategy has been employed to understand the role of ligands on the structural and optical properties of atomically precise 29 atom silver nanoclusters (NCs). By ligand optimization, ∼44-fold quantum yield (QY) enhancement of Ag29(BDT)12–x (DHLA) x NCs (x = 1–6) was achieved, where BDT and DHLA refer to 1,3-benzene-dithiol and dihydrolipoic acid, respectively. High-resolution mass spectrometry was used to monitor ligand exchange, and structures of the different NCs were obtained through density functional theory (DFT). The DFT results from Ag29(BDT)11(DHLA) NCs were further experimentally verified through collisional cross-section (CCS) analysis using ion mobility mass spectrometry (IM MS). An excellent match in predicted CCS values and optical properties with the respective experimental data led to a likely structure of Ag29(DHLA)12 NCs consisting of an icosahedral core with an Ag16S24 shell. Combining the experimental observation with DFT structural analysis of a series of atomically precise NCs, Ag29–y Au y (BDT)12–x (DHLA) x (where y, x = 0,0; 0,1; 0,12 and 1,12; respectively), it was found that while the metal core is responsible for the origin of photoluminescence (PL), ligands play vital roles in determining their resultant PLQY.