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Nanometer-scaled objects are known to have dimension-related properties, but sometimes the assembly of such objects can lead to the emergence of other properties. Here, we show the assembly of atomically precise gold nanoclusters into large fibrillar structures that are featuring excitation-dependent luminescence with an excitation-selective circularly polarized luminescence (CPL), even though all components are achiral. The origin of CPL in the assembly of atomic clusters has been attributed to the hierarchical organization of atomic clusters into fibrillar structures, mediated via a hydrogen bonding interaction with a surfactant. We follow the assembly process both experimentally and computationally showing the advance in the structural formation along with its chiroptical electronic properties, i.e., circular dichroism (CD) and CPL. Our study here can assist in the rational design of materials featuring chiroptical properties, thus leading to a controlled CPL activity.

Fluorophores that emit in the near-infrared (NIR, 700–1700 nm) and have high quantum yields are urgently needed for many technical applications such as organic light-emitting diodes or bioimaging. The design of such chromophores is hampered by the energy gap law, which states that shifting the emission to lower wavelengths is accompanied by a dramatic increase in the nonradiative decay rate. In this article we argue that linear oligomers with J-type excitonic coupling are ideal NIR fluorophores because of the advantageous dependence of the emission energy and the radiative and nonradiative rates on the length Nover which the excitation is delocalized. The lowering of the emission energy due to exciton splitting and the linear increase of the radiative rate with length (super-radiance) are well understood. However, less attention has been paid to the decrease of the nonradiative rate with length, which can compensate for the exponential increase due to the energy gap law. According to the exciton model, the Huang–Rhys factors decrease like N–2while the strength of the nonadiabatic coupling remains approximately constant. Plugging these relations into the Englman–Jortner’s energy gap law, we show that for excitonic coupling that is not too strong the nonradiative rate decreases quickly with N. This phenomenon explains the decrease of the nonradiative rate with length in J-aggregates of carbocyanine dyes and the exceptionally high fluorescence quantum yields of linear ethyne-linked zinc-porphyrin arrays, which seemed to defy the energy gap law.

We report the chemical substitution-mediated doping of silver atoms into Au10SG10(SG: glutathione) catenane nanoclusters (NCs) in a controllable manner. Two levels of doping were conducted leading to two silver-doped Au10–xAgxSG10nanoclusters (with x= 0–2 and x= 1–4). Optical studies reveal that nanoclusters with a high level of doping (x= 1–4) show a blue shift in absorption and a significant red shift of ∼50 nm in the two-photon-excited emission spectrum with respect to pristine Au10SG10. The preservation of the catenane structure is confirmed by comparing the experimental and computational X-ray diffraction patterns and absorption spectra of Au10SG10and its silver-doped analogs. In order to better address the structure–property relationship in such catenane clusters, further theoretical investigations were performed at the DFT level. A high-energy shift of the S1state is evidenced in the calculated one-photon absorption spectra due to a larger s to d gap in silver caused by smaller relativistic effects in comparison to the gold atoms. Furthermore, the red shift in the two-photon excited emission band of the clusters is due to significantly larger calculated relaxation of the first excited state in nanoclusters with a high level of silver doping.

The rhombic dodecahedral nanocluster [Ag14(CCtBu)12Cl]+, which has been structurally characterized using X-ray crystallography, was transferred to the gas phase using electrospray ionization, where it was characterized by ion mobility (IM), vacuum ultraviolet (VUV), and ultraviolet (UV) spectroscopies in conjunction with DFT calculations. IM reveals a single peak, and modeling of the collision cross-section with the X-ray structure suggests that the cluster maintains its condensed phase structure upon transfer to the gas phase. The VUV spectra exhibit rich fragmentation, including: photoionization to give [Ag14(CCtBu)12Cl]2+•with an onset of 8.84 ± 0.08 eV; cluster fission fragmentation via losses of (AgCCtBu)nand (AgCCtBu)n−1(AgCl); and via reductive elimination of (tBuCC)2. Apart from channels associated with photoionization, similar fragment ions are observed in the UVPD spectra, although their relative intensities differ. The TDDFT absorption spectra are symmetry-allowed transitions including Au→ Ag, Eu→ Ag, and Eu→ Egirreducible representations. Comparing the collision cross-sections with the X-ray structures for the related clusters [Ag8Cu6(CCtBu)12Cl]+, [Ag14(CCtBu)12Br]+, and [Ag8Cu6(CCtBu)12Br]+suggests that they maintain their condensed-phase structures in the gas phase. The VUV spectra of [Ag8Cu6(CCtBu)12Cl]+and [Ag14(CCtBu)12Br]+exhibit similar fragmentation channels and ionization onsets (8.86 ± 0.03 and 8.86 ± 0.05, respectively) compared with [Ag14(CCtBu)12Cl]+.

We present a systematic theoretical investigation of the structural and optical properties of thiolate-protected silver clusters with the goal to design species exhibiting strong absorption and fluorescence in the UV–vis spectral range. We show that the optical properties can be tuned by creating systems with different counts of confined electrons within the cluster core. We consider liganded silver complexes with nsilver atoms (Agn) and xligands (Lx) in anionic complexes [AgnLx]−with L = SCH3. Variation of the composition ratio gives rise to systems with (i) zero confined electrons for x= n+ 1, (ii) two confined electrons for x= n– 1, and (iii) four confined electrons for x= n– 3. We show that the number of confined electrons within the cluster core and the geometric structure of the latter are responsible for the spectral patterns, giving rise to intense absorption transitions and fluorescence in the visible or even infrared range. Our results open a perspective for the rational design of stable ligand-protected silver cluster chromophores that might find numerous applications in the field of biosensing.

We present theoretical results based on DFT calculations of the reactivity of binary neutral stoichiometric Zrn-1ScO2nclusters with oxygen radical centers toward CO and acetylene with the aim to build a bridge between clusters and surface models. Following the concept of the same total valence electron count, the studied series of binary clusters mimics cationic stoichiometric (ZrO2)n+species characterized also by the presence of an oxygen radical center. In the case of Zr11ScO24, representing a section of the (ZrO2)nbulk, in addition to the oxygen radical center, the presence of neighboring Zr atoms effectively promotes oxidation reactions toward CO and acetylene, showing the importance of the surrounding of active centers.

Gold(I)– and silver(I)–thiolate oligomers generated under nanoparticle growth conditions have been suggested to play an important role in the growth mechanism of thiolate-protected noble metal clusters. In this work, we explore the formation of isolated noble metal–glutathione complexes by complementing electrospray mass spectrometry and optical action spectroscopy with TDDFT calculations. We have isolated and recorded action spectra of [Au+GSH–2H]−, [Ag+GSH–2H]−, and [3Ag+2GSH–4H]−complexes. Competition between photofragmentation and photodetachment channels related to electron binding energies was observed. Our findings show that, although structural properties of silver and gold metal–glutathione oligomers are similar, their optical properties in the UV range differ substantially. The experimental spectra were interpreted and assigned by comparison with TDDFT simulations, which allowed us to identify the key role of O–metal–S subunits and characterize their optical properties depending on the choice of metal.

The structure and reactivity properties of a series of clusters ZrxO2x+1+(x= 1–3) are investigated using DFT calculations and guided-ion-beam mass spectrometry. Calculations determine the cluster structures containing two oxygen atoms sharing a spin unpaired electron known as a superoxide (O2–). Experiment and theory provide evidence that the size of the cluster has marked influence over the reactivity properties toward C3H6, C4H6, and C2H2. In particular, Zr2O5+is highly reactive for the oxidation of the three hydrocarbons, while ZrO3+only presents substantial reactivity toward butadiene. In addition, Zr3O7+primarily associates the reactants, revealing minor oxidation channels.

The effect of the environmenton doubly charged metallic subunits has been investigated in the gas phase through a combined experimental and theoretical study. The hybrid system consisting of an Ag42+cluster and a tryptophan molecule exhibits an unambiguous optical fingerprint, which can be useful to gain mechanistic insights into the aggregation and growth of nanoparticles (see figure; blue N, gray Ag, green C, red O, turquoise H).

Die Auswirkungen der Umgebungauf doppelt geladene metallische Untereinheiten wurden in der Gasphase im Rahmen einer experimentell/theoretischen Studie untersucht. Das Hybridsystem aus einem Ag4‐Cluster und einem Tryptophanmolekül hat einen eindeutigen optischen „Fingerabdruck“, der helfen kann, Einblicke in den Mechanismus der Aggregation und des Wachstums von Nanopartikeln zu erhalten (siehe Bild; blau N, grau Ag, grün C, rot O, türkis H).

Ein Elektron mehr oder weniger: Um Radikalzentren in neutralen binären Zirconiumoxid‐Clustern zu generieren, wird in kationischen oder anionischen Clustern mit einem Radikalzentrum ein Zr‐Atom gegen ein Metallatom mit einem Elektron mehr (Nb) bzw. weniger (Sc) ausgetauscht. Diese isoelektronischen Systeme vermitteln ähnliche Oxidationen und können einen vollständigen Katalysezyklus durchlaufen (siehe Bild; Zr gelb, Sc grau, O rot, C grün, H türkis, N blau).

For very small nanocluster-based catalysts, the exploration of the influence of the particle size, composition, and support offers precisely variable parameters in a wide material search space to control catalysts’ performance. We present the mechanism of the CO2methanation reaction on the oxidized bimetallic Cu3Pd tetramer (Cu3PdO2) supported on a zirconia model support represented by Zr12O24based on the energy profile obtained from density functional theory calculations on the reaction of CO2and H2. In order to determine the role of the Pd atom, the performance of Cu3PdO2with monometallic Cu4O2at the same support has been compared. Parallel to methane formation, the alternative path of methanol formation at this catalyst has also been investigated. The results show that the exchange of a single atom in Cu4with a single Pd atom improves catalyst/s performance via lowering the barriers associated with hydrogen dissociation steps that occur on the Pd atom. The above-mentioned results suggest that the doping strategy at the level of single atoms can offer a precise control knob for designing new catalysts with desired performance.

The shape of theS0,S1, andT1 potential energy surfaces of formaldimine, CH2=NH, is explored in the two-dimensional subspace defined by the twisting and linear inversion motions which correspond to the geometricalsyn-anti isomerization, using anab initio large-scale CI method. Minima in theS1 andT1 surfaces as well as aS0-S1 conical intersection are identified and the photoisomerization mechanism is discussed.

The general Hartree-Fock energy in the frontier orbital model in the terms of independent variables is given. The existence conditions for extrema of this expression are derived and their relation with various types of solutions of the HF problem as RHF, UHF and complex wavefunctions is shown. The connection between overall properties of the energy surface and the local properties i.e. the stability and instability conditions of various kinds is demonstrated. The conditions for the occurrence of “strange” HF solutions are expressed in terms of quantities characterizing the correlation effects. This shows explicitly that the lack of respecting the electronic correlation is the reason for the occurrence of the “strange” HF solutions for the molecular configurations which exhibit a certain amount of diradical character.

The commutator relation between the Hartree-Fock matrix and the one-electron density matrix in Fukui's frontier molecular orbital model has been used to investigate the various kinds of ending of the customary iterative SCF procedure. Step by step description of the iterative SCF procedure has been given in an illustrative graphical way. There is a close connection among the symmetry nonadapted RHF solution for symmetrical molecules, the UHF solution for the closed shell molecules, the complex HF solution and the occurrence of oscillation for the iterative procedure. It has been explicitly shown that the nonconvergence of the usual iterative procedure occurs when the Coulombic interaction between not fully coupled spins of the molecular systems with a certain amount of diradical character is sufficiently weak. The results of the analysis concerning the properties of the Hartree-Fock approach are generalized for the asymmetrical molecules.