The most characteristic feature of planar π-aromatics is the ability to sustain a long-range shielding cone under a magnetic field oriented in a specific direction. In this article, we showed that similar magnetic responses can be found in σ-aromatic and spherical aromatic systems. For [Au 13 ] 5+ , long-range characteristics of the induced magnetic field in the bare icosahedral core are revealed, which are also found in the ligand protected [Au 25 (SH) 18 ] − model, proving its spherical aromatic properties, also supported by the AdNDP analysis. Such properties are given by the 8-ve of the structural core satisfying the Hirsch 2( N + 1) 2 rule, which is also found in the isoelectronic [M@Au 12 ] 4+ core, a part of the [MAu 24 (SR) 18 ] 2− (M = Pd, Pt) cluster. This contrasts with the [M@Au 12 ] 6+ core in [MAu 24 (SR) 18 ] 0 (M = Pd, Pt), representing 6-ve superatoms, which exhibit characteristics of planar σ-aromatics. Our results support the spherical aromatic character of stable superatoms, whereas the 6-ve intermediate electron counts satisfy the 4 N + 2 rule (applicable for both π- and σ-aromatics), showing the reversable and controlled interplay between 3D spherical and 2D σ-aromatic clusters.
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Characterization of Pt-doping effects on nanoparticle emission: a theoretical look at Au 24 Pt(SH) 18 and Au 24 Pt(SC 3 H 7 ) 18
Developments in nanotechnology have made the creation of functionalized materials with atomic precision possible. Thiolate-protected gold nanoclusters, in particular, have become the focus of study in literature as they possess high stability and have tunable structure–property relationships. In addition to adjustments in properties due to differences in size and shape, heteroatom doping has become an exciting way to tune the properties of these systems by mixing different atomic d characters from transition metal atoms. Au 24 Pt(SR) 18 clusters, notably, have shown incredible catalytic properties, but fall short in the field of photochemistry. The influence of the Pt dopant on the photoluminescence mechanism and excited state dynamics has been investigated by a few experimental groups, but the origin of the differences that arise due to doping has not been clarified thoroughly. In this paper, density functional theory methods are used to analyze the geometry, optical and photoluminescent properties of Au 24 Pt(SR) 18 in comparison with those of [Au 25 (SR) 18 ] 1− . Furthermore, as these clusters have shown slightly different geometric and optical properties for different ligands, the analysis is completed with both hydrogen and propyl ligands in order to ascertain the role of the passivating ligands.
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- NSF-PAR ID:
- 10406133
- Date Published:
- Journal Name:
- Faraday Discussions
- Volume:
- 242
- ISSN:
- 1359-6640
- Page Range / eLocation ID:
- 464 to 477
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)We investigate the excited electron dynamics in [Au 25 (SR) 18 ] −1 (R = CH 3 , C 2 H 5 , C 3 H 7 , 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, CH 3 , C 2 H 5 , C 3 H 7 , 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 (SCH 3 ) 18 ] −1 nanocluster to understand how independent electron and hole relaxations contribute to the overall relaxation dynamics.more » « less
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Understanding the critical roles of ligands ( e.g. thiolates, SR) in the formation of metal nanoclusters of specific sizes has long been an intriguing task since the report of ligand exchange-induced transformation of Au 38 (SR) 24 into Au 36 (SR′) 24 . Herein, we conduct a systematic study of ligand exchange on Au 38 (SC 2 H 4 Ph) 24 with 21 incoming thiols and reveal that the size/structure preference is dependent on the substituent site. Specifically, ortho -substituted benzenethiols preserve the structure of Au 38 (SR) 24 , while para - or non-substituted benzenethiols cause its transformation into Au 36 (SR) 24 . Strong electron-donating or -withdrawing groups do not make a difference, but they will inhibit full ligand exchange. Moreover, the crystal structure of Au 38 (SR) 24 (SR = 2,4-dimethylbenzenethiolate) exhibits distinctive π⋯π stacking and “anagostic” interactions (indicated by substantially short Au⋯H distances). Theoretical calculations reveal the increased energies of frontier orbitals for aromatic ligand-protected Au 38 , indicating decreased electronic stability. However, this adverse effect could be compensated for by the Au⋯H–C interactions, which improve the geometric stability when ortho -substituted benzenethiols are used. Overall, this work reveals the substituent site effects based on the Au 38 model, and highlights the long-neglected “anagostic” interactions on the surface of Au-SR NCs which improve the structural stability.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2FD00110A
