6,264 research outputs found
Au36(SePh)24 nanomolecules: Synthesis, optical spectroscopy and theoretical analysis
No full textHere, we report the synthesis of selenophenol (HSePh) protected Au36(SePh)24 nanomolecules via a ligand-exchange reaction of 4-tert-butylbenzenethiol (HSPh-tBu) protected Au36(SPh-tBu)24 with selenophenol, and its spectroscopic and theoretical analysis. Matrix assisted laser desorption ionization (MALDI) mass spectrometry, electrospray ionization (ESI) mass spectrometry and optical characterization confirm that the composition of the as synthesized product is predominantly Au36(SePh)24 nanomolecules. Size exclusion chromatography (SEC) was employed to isolate the Au36(SePh)24 and temperature dependent optical absorption studies and theoretical analysis were performed. Theoretically, an Independent Component Maps of Oscillator Strength (ICM-OS) analysis of simulated spectra shows that the enhancement in absorption intensity in Au36(SePh)24 with respect to Au36(SPh)24 can be ascribed to the absence of interference and/or increased long-range coupling between interband metal core and ligand excitations. This work demonstrates and helps to understand the effect of Au–Se bridging on the properties of gold nanomolecules
Principles of Optical Spectroscopy of Aromatic Alloy Nanomolecules: Au36-xAgx(SPh-tBu)24
No full textHere, we report the synthesis and experimental and theoretical characterizations of Au36−xAgx(SPh-tBu)24 alloy nanomolecule to atomic precision. By changing the incoming gold-to-silver metal ratio during the synthesis of crude mixture, up to eight silver atoms can be incorporated into Au36(SPhtBu) 24, as theoretically confirmed and rationalized in terms of its core and staple structure. Tuning of optical response by Ag doping is strongly affected by aromatic conjugation and qualitatively different with respect to the aliphatic case, with a strikingly nonmonotonic behavior of absorption intensity in the low- and high-energy regions, in fair agreement with
theoretical predictions, as rationalized via an original analysis tool: independent component mapping of oscillatory strength plots
Au279(SR)84: The Smallest Gold Thiolate Nanocrystal That Is Metallic and the Birth of Plasmon
No full textWe report a detailed study on the optical properties of Au279(SR)84 using
steady-state and transient absorption measurements to probe its metallic nature, timedependent
density functional theory (TDDFT) studies to correlate the optical spectra,
and density of states (DOS) to reveal the factors governing the origin of the collective
surface plasmon resonance (SPR) oscillation. Au279 is the smallest identified gold
nanocrystal to exhibit SPR. Its optical absorption exhibits SPR at 510 nm. Powerdependent
bleach recovery kinetics of Au279 suggests that electron dynamics dominates
its relaxation and it can support plasmon oscillations. Interestingly, TDDFT and DOS
studies with different tail group residues (−CH3 and −Ph) revealed the important role
played by the tail groups of ligands in collective oscillation. Also, steady-state and timeresolved
absorption for Au36, Au44, and Au133 were studied to reveal the molecule-to-metal evolution of aromatic AuNMs. The
optical gap and transient decay lifetimes decrease as the size increases
Au24(SAdm)16 Nanomolecules: X-ray Crystal Structure, Theoretical Analysis, Adaptability of Adamantane Ligands to Form Au23(SAdm)16 and Au25(SAdm)16, and Its Relation to Au25(SR)18
No full textHere we present the crystal structure, experimental
and theoretical characterization of a Au24(SAdm)16
nanomolecule. The composition was verified by X-ray
crystallography and mass spectrometry, and its optical and
electronic properties were investigated via experiments and firstprinciples
calculations. Most importantly, the focus of this work
is to demonstrate how the use of bulky thiolate ligands, such as
adamantanethiol, versus the commonly studied phenylethanethiolate
ligands leads to a great structural flexibility, where the
metal core changes its shape from five-fold to crystalline-like
motifs and can adapt to the formation of Au24±1(SAdm)16, namely, Au23(SAdm)16, Au24(SAdm)16, and Au25(SAdm)16. The basis
for the construction of a thermodynamic phase diagram of Au nanomolecules in terms of ligands and solvent features is also
outlined
Au38(SPh)24: Au38 Protected with Aromatic Thiolate Ligands
No full textAu38(SR)24 is one of the most extensively investigated gold nanomolecules along with Au25(SR)18 and Au144(SR)60. However, so far it has only been prepared using aliphatic-like ligands, where R = −SC6H13, −SC12H25 and −SCH2CH2Ph. Au38(SCH2CH2Ph)24 when reacted with HSPh undergoes core-size conversion to Au36(SPh)24, and existing literature suggests that Au38(SPh)24 cannot be synthesized. Here, contrary to prevailing knowledge, we demonstrate that Au38(SPh)24 can be prepared if the ligand exchanged conditions are optimized, under delicate conditions, without any formation of Au36(SPh)24. Conclusive evidence is presented in the form of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), electrospray ionization mass spectra (ESI-MS) characterization, and optical spectra of Au38(SPh)24 in a solid glass form showing distinct differences from that of Au38(S-aliphatic)24. Theoretical analysis confirms experimental assignment of the optical spectrum and shows that the stability of Au38(SPh)24 is not negligible with respect to that of its aliphatic analogous, and contains a significant component of ligand−ligand attractive interactions. Thus, while Au38(SPh)24 is stable at RT, it converts to Au36(SPh)24 either on prolonged etching (longer than 2
hours) at RT or when etched at 80 °C
Ligand-Enhanced Optical Response of Gold Nanomolecules and Its Fragment Projection Analysis: The Case of Au30(SR)18
No full textHere we investigate via first-principles simulations
the optical absorption spectra of three different
Au30(SR)18 monolayer-protected clusters (MPC):
Au30(StBu)18, Au30(SPh)18, and Au30(SPh-pNO2)18.
Au30(StBu)18 is known in the literature, and its crystal structure
is available. In contrast, Au30(SPh)18 and Au30(SPh-pNO2)18
are two species that have been designed by replacing the tertbutyl
organic residues of Au30(StBu)18 with aromatic ones so as
to investigate the effects of ligand replacement on the optical
response of Au nanomolecules. By analogy to a previously
studied Au23(SR)16
− anionic species, despite distinct differences
in charge and chemical composition, a substantial ligand
enhancement of the absorption intensity in the optical region
is also obtained for the Au30(SPh-pNO2)18 MPC. The use of
conjugated aromatic ligands with properly chosen electron-withdrawing substituents and exhibiting steric hindrance so as to also
achieve charge decompression at the surface is therefore demonstrated as a general approach to enhancing the MPC
photoabsorption intensity in the optical region. Additionally, we here subject the ligand-enhancement phenomenon to a detailed
analysis based on the fragment projection of electronic excited states and on induced transition densities, leading to a better
understanding of the physical origin of this phenomenon, thus opening avenues to its more precise control and exploitation
Au21S(SAdm)15: An Anisotropic Gold Nanomolecule. Optical and Photoluminescence Spectroscopy and First-Principles Theoretical Analysis
No full textWe introduce a class of gold nanomolecules exhibiting anisotropy as a major feature by reporting steady-state and time-resolved photoluminescence and anisotropy measurements and in-depth theoretical analysis of energetics and optical response of a recently synthesized Au21S(SAdm)15 nanomolecule (SAdm = adamantanethiol). Starting from single-crystal X-ray data showing that Au21S(SAdm)15 exhibits a symmetry-broken structure, we unambiguously demonstrate how this translates into a striking anisotropy of its properties, for example, of its (chiro)optical absorption spectrum of great promise for sensing, optoelectronic, and electrochemical applications, and argue about the abundance and general significance of this class of compounds
Au21S(SAdm)15: Crystal Structure, Mass Spectrometry, Optical Spectroscopy, and First-Principles Theoretical Analysis
No full textHere we report X-ray crystal structure, spectroscopic and theoretical characterization of Au21S(SAdm)15 (SAdm = adamantanethiol). Single-crystal X-ray diffraction shows that the Au21S(SAdm)15 nanomolecule exhibits a Au12 cuboctahedral core missing one vertex surrounded by a single μ3 sulfur atom (sulfide), five bridging thiols, two additional Au atoms, one monomeric Au(SR)2, and two trimeric Au3(SR)4 staples, with the two trimeric staples being linked through a Au2(SR) unit with a thiolate ligand in μ4 coordination. Compositional, electronic, optical, and structural features of this compound are clarified via nanoelectrospray ionization mass spectrometry (nESI-MS), matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), low-temperature UV−vis spectroscopy, and first-principles analysis
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