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Transition metal dichalcogenide monolayers have demonstrated a number of exquisite optical and electrical properties. Here, the authors report the optical modification of topographical and optical properties of monolayer MoS2 with femtosecond pulses under an inert atmosphere. A formation of three‐dimensional structures on monolayer MoS2 with tunable height up to ≈20 nm is demonstrated. In contrast to unmodified monolayer MoS2, these optically modified structures show significantly different optical properties, such as lower photoluminescence intensity and longer fluorescence lifetime. The results suggest a novel way to modify transition metal dichalcogenide materials for mechanic, electronic and photonic applications. [ABSTRACT FROM AUTHOR]

Numerical wave packet simulations are performed for studying coherent anti-Stokes Raman scattering (CARS) for CN radicals. Electronic coherence is created by femtosecond laser pulses between the X 2Σ and B 2Σ states. Due to the large energy separation of vibrational states, the wave packets are superpositions of rotational states only. This allows for a specially detailed inspection of the second- and third-order coherences by a two-dimensional imaging approach. We present the time-frequency domain images to illustrate the intra- and intermolecular interferences, and discuss the procedure to rationally control and experimentally detect the interferograms in solid Xe environment. [ABSTRACT FROM AUTHOR]

The formation of iodine clusters in a solid krypton matrix is analyzed by using resonance Raman spectroscopy. The larger, bulklike shift has appeared when the iodine molecule is coordinated from two opposite directions as in the case of a pentamer and higher clusters and the structural motif of crystalline iodine is recognized in the clusters, starting from the pentamer.

Infrared and Raman spectroscopy are used for studying the structure and properties of a 1:1 iodine-benzene complex isolated in an inert krypton matrix at low temperature. The studies have shown that the [I.sub.2]-Bz complex structure is not axial but of above-bond type, identically with other halogen-benzene complexes.

The absorption spectrum of I2in solid Xe shows resolvedzero-phonon lines and phonon side bands near the origin of the B←Xtransition (550–625 nm). The long-lived |B⟩⟨X| coherence in this energy range(T2= 600 fs on average) emerges as vibrationallyunrelaxed fluorescence in resonance Raman (RR) spectra. Upon excitationin the structureless continuum at 532 nm, the oscillatory RR progressionexhibits electronic dephasing time of T2= 150 fs. Two RR progressions with markedly different vibrationalcoherence on the X-state are observed. The main progression of sharpovertones (T2> 21 ps) is assignedtomolecules trapped in double-substitution sites. The minor progression,which shows dephasing times T2= 6–0.6ps for v= 1–8, is assigned to molecules intriple-substitution sites. The line progressions allow a detailedcharacterization of the solvated B- and X-state potentials. Time-resolvedcoherent anti-Stokes Raman scattering is used to probe selected vibrationalcoherences on the X-state. Assignments are obtained through moleculardynamics simulations, which reproduce the relative dephasing ratesbetween the two sites, clarify the role of rotation-translation dynamics,and enable quantum dynamics simulations of the spectra by the potentialsof mean force that accurately describe the molecule–surroundinginteractions. [ABSTRACT FROM AUTHOR]

Optical absorption of a gold nanocluster of 102 Au atoms protected by 44 para-mercaptobenzoic acid (p-MBA) ligands is measured in the range of 0.05-6.2 eV (mid-IR to UV) by a combination of several techniques for purified samples in solid and solution phases. The results are compared to calculations for a model cluster Au102(SMe)44 based on the time-dependent density functional theory in the linear-response regime and using the known structure of Au102(p-MBA)44. The measured and calculated molar absorption coefficients in the NIR-vis region are comparable, within a factor of 2, in the absolute scale. Several characteristic features are observed in the absorption in the range of 1.5-3.5 eV. The onset of the electronic transitions in the mid-IR region is experimentally observed at 0.45 ± 0.05 eV which compares well with the lowest calculated transition at 0.55 eV. Vibrations in the ligand layer give rise to fingerprint IR features below the onset of low-energy metal-to-metal electronic transitions. Partial exchange of the p-MBA ligand to glutathione does not affect the onset of the electronic transitions, which indicates that the metal core of the cluster is not affected by the ligand exchange. The full spectroscopic characterization of the Au102(p-MBA)44 reported here for the first time gives benchmarks for further studies of manipulation and functionalization of this nanocluster to various applications. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide, optical modification, photoluminescence, topography, 2D materials Keywords: molybdenum disulfide; optical modification; photoluminescence; topography; 2D materials EN molybdenum disulfide optical modification photoluminescence topography 2D materials 1 1 1 05/26/21 20210521 NES 210521 In article number 2002119, Mika Pettersson, Zhipei Sun, and co-workers demonstrate an optical modification process that simultaneously creates topographical structures and alters the optical properties of MoS SB 2 sb monolayer. Optical Modification of Monolayer MoS2: Deterministic Modification of CVD Grown Monolayer MoS2 with Optical Pulses (Adv. [Extracted from the article]

Interactions between an atomically precise gold nanocluster Au 102 ( p -MBA) 44 ( p -MBA = para mercaptobenzoic acid) and a fluorescent organic dye molecule (KU, azadioxatriangulenium) are studied. In solution, the constituents form spontaneously a weakly bound complex leading to quenching of fluorescence of the KU dye via energy transfer. The KU can be separated from the complex by lowering pH, leading to recovery of fluorescence, which forms a basis for an optical reversible pH sensor. However, the sensor is not a stable entity, which could be delivered inside cells. For this purpose, a covalently bound hybrid is synthesized by linking the KU dye to the ligand layer of the cluster via an ester bond. Covalent linking facilitates entry of the cluster-dye hybrids into cells via endocytosis. Inside cells, the hybrids accumulate in endosomes where Au 102 releases its cargo via hydrolysis of the ester bond. Changes of the local pH inside endosomes regulate reversible fluorescence due to variations in the interactions between the Au 102 cluster and the dye. This work presents a concept for delivering reporter molecules into cells by using atomically precise gold nanoclusters as carriers and paves the way for future developments of cluster-reporter sensors for in vivo measurements of e.g. absolute pH values or ion concentrations., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We present the synthesis, separation, and characterization of covalently-bound multimers of para-mercaptobenzoic acid (p-MBA) protected gold nanoclusters. The multimers were synthesized by performing a ligand-exchange reaction of a pre-characterized Au 102 (p-MBA) 44 nanocluster with biphenyl-4,4'-dithiol (BPDT). The reaction products were separated using gel electrophoresis yielding several distinct bands. The bands were analyzed by transmission electron microscopy (TEM) revealing monomer, dimer, and trimer fractions of the nanocluster. TEM analysis of dimers in combination with molecular dynamics simulations suggest that the nanoclusters are covalently bound via a disulfide bridge between BPDT molecules. The linking chemistry is not specific to Au 102 (p-MBA) 44 . The same approach yields multimers also for a larger monodisperse p-MBA-protected cluster of approximately 250 gold atoms, Au ∼250 (p-MBA) n . While the Au 102 (p-MBA) 44 is not plasmonic, the Au ∼250 (p-MBA) n nanocluster supports localized surface plasmon resonance (LSPR) at 530 nm. Multimers of the Au ∼250 (p-MBA) n exhibit additional transitions in their UV-vis spectrum at 630 nm and 810 nm, indicating the presence of hybridized LSPR modes. Well-defined structures and relatively small sizes make these systems excellent candidates for connecting ab initio theoretical studies and experimental quantum plasmonics. Moreover, our work opens new possibilities in the controlled synthesis of advanced monodisperse nanocluster superstructures.

The properties of the 1:1 iodine-benzene complex isolated in a solid Kr matrix at low temperatures have been studied using UV-vis absorption, FTIR, resonance Raman, and femtosecond coherent anti-Stokes Raman spectroscopy (fs-CARS). The use of all these techniques on similar samples provides a wide view on the spectroscopic properties of the complex and allows comparison and combination of the results from different methods. The results for the complex cover its structure, the changes in the iodine molecule's vibrational frequencies and electronic absorption spectrum upon complexation, and the dynamics of the complexed I(2) molecule on both ground and excited electronic states. In addition, polarization beats between uncomplexed benzene and iodine molecules are detected in the fs-CARS spectra, showing an amplification of an electronically nonresonant CARS signal by the resonant iodine signal. The possibility of controlling the charge-transfer reaction of the I(2)-Bz complex using the excitation of a well-defined ground-state vibrational wavepacket, according to the Tannor-Rice-Kosloff scheme, is discussed on the basis of the experimental findings.