Category Archives: ChemPhysChem

Experimental and Theoretical Structure Elucidation of the [2 : 1] Complex Ion of Carbo[n]helicene with n=6, 7 and 8 and Ag+

Posted on 6 September 2023 by

Gas-phase complexes of [n]helicenes with n=6, 7 and 8 and silver(I) cation are generated. Besides the well-established [1 : 1] helicene/Ag⁺-complex in which the helicene provides a tweezer-like surrounding for the Ag⁺, there is also a [2 : 1] complex formed. The second helicene attaches via π-π stacking to the first helicene of the [1 : 1] tweezer complex. Using [n]helicene mixtures, tweezer complexes of Ag⁺ are preferably formed with the larger helicenes.

Abstract

Gas-phase complexes of [n]helicenes with n=6, 7 and 8 and the silver(I) cation are generated utilizing electrospray ionization mass spectrometry (ESI-MS). Besides the well-established [1 : 1] helicene/Ag⁺-complex in which the helicene provides a tweezer-like surrounding for the Ag⁺, there is also a [2 : 1] complex formed. Density functional theory (DFT) calculations in conjunction with energy-resolved collision-induced dissociation (ER-CID) experiments reveal that the second helicene attaches via π-π stacking to the first helicene, which is part of the pre-formed [1 : 1] tweezer complex with Ag⁺. For polycyclic aromatic hydrocarbons (PAHs) of planar structure, the [2 : 1] complex with silver(I) is typically structured as an Ag⁺-bound dimer in which the Ag⁺ would bind to both PAHs as the central metal ion (PAH–Ag⁺–PAH). For helicenes, the Ag⁺-bound dimer is of similar thermochemical stability as the π-π stacked dimer, however, it is kinetically inaccessible. Coronene (Cor) is investigated in comparison to the helicenes as an essentially planar PAH. In analogy to the π-π stacked dimer of the helicenes, the Cor−Ag⁺−Cor−Cor complex is also observed. Competition experiments using [n]helicene mixtures reveal that the tweezer complexes of Ag⁺ are preferably formed with the larger helicenes, with n=6 being entirely ignored as the host for Ag⁺ in the presence of n=7 or 8.

Facile Formation of Sulfurized Nanorod‐Like ZnO/Zn(OH)2 and Hierarchical Flower‐Like γ‐Zn(OH)2/ϵ‐Zn(OH)2 from a Green Synthesis and Application as Luminescent Solar Concentrator

Posted on 4 September 2023 by

Green synthesis of sulfurized nanorod (NR)-like ZnO/Zn(OH)₂ and hierarchical flower-like γ-Zn(OH)₂/ϵ-Zn(OH)₂ is reported for luminescent solar concentrators (LSC)-photovoltaic (PV) system. This combination shows a superior solar PV performance over the non-sulfurized analogues.

Abstract

This research endeavors to overcome the significant challenge of developing materials that simultaneously possess photostability and photosensitivity to UV-visible irradiation. Sulfurized nanorod (NR)-like ZnO/Zn(OH)₂ and hierarchical flower-like γ-Zn(OH)₂/ϵ-Zn(OH)₂ were identified from XRD diffraction patterns and Raman vibrational modes. The sulfurized material, observed by FEG-SEM and TEM, showed diameters ranging from 10 and 40 nm and lengths exceeding 200 nm. The S²⁻ ions intercalated Zn²⁺, modulating NRs to dumbbell-like microrods. SAED and HRTEM illustrated the atomic structure in (101) crystal plane. Its direct band gap of 3.0 eV was attributed to the oxygen vacancies, which also contribute to the deep-level emissions at 422 and 485 nm. BET indicated specific surface area of 4.4 m² g⁻¹ and pore size as mesoporosity, which are higher compared to the non-sulfurized analogue. These findings were consistent with the observed photocurrent, photostability and photoluminescence (PL), further supporting the suitability of sulfurized NR-like ZnO/Zn(OH)₂ as a promising candidate for Luminescent solar concentrators (LSC)-photovoltaic (PV) system.

Interfacial Coupling of Graphene with Nickel Nanoparticles for Water Splitting and Urea Oxidation: A Spectroelectrochemical Investigation

Posted on 1 September 2023 by nSanjit Saha, nGour Mohan Dasn

Efficient HER, OER, and UOR catalytic properties are achieved by interfacial coupling of 2D graphene and Ni-nano particles. Spectro-electrochemical study of Ni/graphene films of various stoichiometry reveals the dependence of the catalytic property on the synergistic interactions of graphene with Ni-nano particles.

Abstract

Nickel nanoparticle and graphene interfaces of various stoichiometries were created through electrodeposition techniques. The catalytic behavior of the electrodeposited films was investigated through spectro-electrochemical methodologies. UV-vis absorbance spectra of the electrodeposited films are significantly different in the air and alkaline medium. Furthermore, UV-vis and Raman spectroscopy confirmed the coupling of Ni nanoparticles (Ni-NP) with the graphene framework, along with NiO and Ni(OH)₂. A combination of Raman and impedance spectroscopy revealed that the surface adsorption and charge transfer properties of the electrodeposited films are entirely dependent on the defects on graphene structure as well as distribution of Ni-NP on graphene. The electrodeposited films possess heterogeneous catalytic properties with a low overpotential of 50 mV (10 mA/cm⁻²) for hydrogen evolution reaction, as well as 601 mV and 391 mV (at 50 mA/cm⁻²) for the oxygen evolution reaction and urea oxidation reaction, respectively. In addition, eelectrodeposited samples show extraordinary overall water splitting performance by achieving a current density of 10 mA/cm² at a very low applied potential of 1.38 V. This synergistic coupling of Ni and graphene renders the electrodeposited samples promising candidates as electrodes for overall water splitting in alkaline and urea-supplemented solutions.

Role of the Residue Q1919 in Increasing Kinase Activity of G2019S LRRK2 Kinase: A Computational Study

Posted on 31 August 2023 by

Hydrogen bonding of S1179 with R1077 and E1078 in S1 state and S2 state are responsible for their stability and thus, increase the kinase activity.

Abstract

Mutations in multi-domain leucine-rich repeat kinase 2 (LRRK2) have been an interest to researchers as these mutations are associated with Parkinson's disease. G2019S mutation in LRRK2 kinase domain leads to the formation of additional hydrogen bonds by S2019 which results in stabilization of the active state of the kinase, thereby increasing kinase activity. Two additional hydrogen bonds of S2019 are reported separately. Here, a mechanistic picture of the formation of additional hydrogen bonds of S2019 with Q1919 (also with E1920) is presented using ‘active’ Roco4 kinase as a homology model and its relationship with the stabilization of the ‘active’ G2019S LRRK2 kinase. A conformational flipping of residue Q1919 was found which helped to form stable hydrogen bond with S2019 and made ‘active’ state more stable in G2019S LRRK2. Two different states were found within the ‘active’ kinase with respect to the conformational change (flipping) in Q1919. Two doubly-mutated systems, G2019S/Q1919A and G2019S/E1920 K, were studied separately to check the effect of Q1919 and E1920. For both cases, the stable S2 state was not formed, leading to a decrease in kinase activity. These results indicate that both the additional hydrogen bonds of S2019 (with Q1919 and E1920) are necessary to stabilize the active G2019S LRRK2.

Raman Spectroscopy of Formamidinium‐Based Lead Mixed‐Halide Perovskite Bulk Crystals

Posted on 31 August 2023 by

Halide doping in perovskites helps to improve the stability of the structure, which is very important for solar-cell applications. Raman spectroscopy and DFT calculations prove to be a combination of powerful techniques for investigating the structure-property relations of perovskites.

Abstract

In recent years, there has been an impressively fast technological progress in the development of highly efficient lead halide perovskite solar cells. Nonetheless, the stability of perovskite films and associated solar cells remains a source of uncertainty and necessitates sophisticated characterization techniques. Here, we report low- to mid-frequency resonant Raman spectra of formamidinium-based lead mixed-halide perovskites. The assignment of the different Raman lines in the measured spectra is assisted by DFT simulations of the Raman spectra of suitable periodic model systems. An important result of this work is that both experiment and theory point to an increase of the stability of the perovskite structure with increasing chloride doping concentration. In the Raman spectra, this is reflected by the appearance of new lines due to the formation of hydrogen bonds. Thus, higher chloride doping results in less torsional motion and lower asymmetric bending contributing to higher stability. This study yields a solid basis for the interpretation of the Raman spectra of formamidinium-based mixed-halide perovskites, furthering the understanding of the properties of these materials, which is essential for their full exploitation in solar cells.

Calculation of Ionization, Excitation and Electron Capture Cross Sections for Be4++H(2s, 2p) Collisions

Posted on 28 August 2023 by nClara Illescasn

Collisions between (excited) hydrogen atoms and beryllium impurity ions are expected to occur inside fusion reactors and the cross sections of all inelastic processes are then needed. A comparative study of H(2s) and H(2p) targets in collision with Be⁴⁺ ions at fusion-relevant energies is presented.

Abstract

A computational study of Be⁴⁺+H(2s, 2p) collisions has been carried out employing the Classical Trajectory Monte Carlo (CTMC) method for the impact energy range from 20 keV/u to 1000 keV/u. The integral n partial cross sections for H(n) excitation and Be³⁺(n) electron capture and, the total ionization and electron capture cross sections are calculated and compared to recent semiclassical results. A general good agreement is observed for the n partial and total electron capture and ionization cross sections. The comparative study of the three inelastic processes show no significant differences between both excited targets.

Remarkable Enhancement of Hole Mobility of Novel DA‐D’‐AD Small Molecules by Thermal Annealing: Effect of the D’‐Bridge Block.

Posted on 25 August 2023 by

Four novel conjugated small molecules (SM) are designed as organic semiconductor materials. Thermal treatment is shown as a powerful approach to control the morphology of SM-based thin films. Remarkable enhancement of hole mobilities of ca. 50 times is achieved for films based on compounds with triisiopropylsilyl-functionalized benzodithiophene cores.

Abstract

Conjugated small molecules are advanced semiconductor materials with attractive physicochemical and optoelectronic properties enabling the development of next-generation electronic devices. The charge carrier mobility of small molecules strongly influences the efficiency of organic and hybrid electronics based on them. Herein, we report the synthesis of four novel small molecules and their investigation with regard to the impact of molecular structure and thermal treatment of films on charge carriers’ mobility. The benzodithiophene-containing compounds (BDT) were shown to be more promising in terms of tuning the morphology upon thermal treatment. Impressive enhancement of hole mobilities by more than 50 times was found for annealed films based on a compound M4 comprising triisopropylsilyl-functionalized BDT core. The results provide a favorable experience and strategy for the rational design of state-of-the-art organic semiconductor materials (OSMs) and for improving their charge-transport characteristics.

Electronic Structure of the Low‐Lying States of the Triatomic MoS2 Molecule: The Building Block of 2D MoS2

Posted on 24 August 2023 by nMarkella A. Mermigki, nIoannis Karapetsas, nDemeter Tzelin

The triatomic MoS₂ molecule is the building component of solid MoS₂. In this work, the electronic structure and chemical bonding of 16 low-lying states of triatomic MoS₂ are studied. The low-lying septet states of triatomic MoS₂ are found to be involved in the material as a building block, explaining the variety of its morphologies.

Abstract

Molybdenum disulfide (MoS₂) is the building component of 1D-monolayer, 2D-layered nanosheets and nanotubes having many applications in industry, and it is detected in various molecular systems observed in nature. Here, the electronic structure and the chemical bonding of sixteen low-lying states of the triatomic MoS₂ molecule are investigated, while the connection of the chemical bonding of the isolated MoS₂ molecule to the relevant 2D-MoS₂, is emphasized. The MoS₂ molecule is studied via DFT and multireference methodologies, i. e., MRCISD(+Q)/aug-cc-pVQZ(−PP)_Mo. The ground state, ³B₁, is bent (Mo−S=2.133 Å and ϕ(SMoS)=115.9°) with a dissociation energy to atomic products of 194.7 kcal/mol at MRCISD+Q. In the ground and in the first excited state a double bond is formed between Mo and each S atom, i. e., . These two states differ in which d electrons of Mo are unpaired. The Mo−S bond distances of the calculated states range from 2.108 to 2.505 Å, the SMoS angles range from 104.1 to 180.0°, and the Mo−S bonds are single or double. Potential energy curves and surfaces have been plotted for the ³B₁, ⁵A₁ and ⁵B₁ states. Finally, the low-lying septet states of the triatomic molecule are involved in the material as a building block, explaining the variety of its morphologies.

Photoexcited Carrier Transfer in CuInS2 Nanocrystal Assembly by Suppressing Resonant‐Energy Transfer

Posted on 23 August 2023 by

Photoexcited carrier transfer in high-density assemblies of Cd- and Pb-free semiconductor nanocrystals of chalcopyrite CuInS₂ is investigated. By suppressing the competing process via excitation-energy transfer between nanocrystals, thermally activated scheme of excited carrier transfer is observed, and their characteristic parameters are determined.

Abstract

High-density assemblies or superlattice structures composed of colloidal semiconductor nanocrystals have attracted attention as key materials for next-generation photoelectric conversion devices such as quantum-dot solar cells. In these nanocrystal solids, unique transport and optical phenomena occur due to quantum coupling of localized energy states, charge-carrier hopping, and electromagnetic interactions among closely arranged nanocrystals. In particular, the photoexcited carrier dynamics in nanocrystal solids is important because it significantly affects various device parameters. In this study, we report the photoexcited carrier dynamics in a solid film of CuInS₂ nanocrystals, which is one of the potential nontoxic substitutes with Cd- and Pb-free compositions. Meanwhile, these subjects have been extensively studied in nanocrystal solids formed by CdSe and PbS systems. A carrier-hopping mechanism was confirmed using temperature-dependent photoluminescence spectroscopy, which yielded a typical value of the photoexcited carrier-transfer rate of (2.2±0.6)×10⁷ s⁻¹ by suppressing the influence of the excitation-energy transfer.

Tunable Gas‐Gas Reactions through Nanobubble Pathway

Posted on 23 August 2023 by nRuiyi Zhang, nYa Gao, nLan Chen, nDexing Li, nGuanglu Gen

The feasibility of gas-gas reaction between H₂ and O₂ bulk nanobubbles is demonstrated, which deepens the understanding on the non-combustion gas-gas reaction mechanism in nanoscale space. It also provides new pathways for green energy conversion and synthesis of many intermediate and final products, which are inaccessible under mild conditions.

Abstract

Combustible gas-gas reactions usually do not occur spontaneously upon mixing without ignition or other triggers to lower the activation energy barrier. Nanobubbles, however, could provide such a possibility in solution under ambient conditions due to high inner pressure and catalytic radicals within their boundary layers. Herein, a tunable gas-gas reaction strategy via bulk nanobubble pathway is developed by tuning the interface charge of one type of bulk nanobubble and promoting its fusion and reaction with another, where the reaction-accompanied size and number concentration change of the bulk nanobubbles and the corresponding thermal effect clearly confirm the occurrence of the nanobubble-based H₂/O₂ combustion. In addition, abundant radicals can be detected during the reaction, which is considered to be critical to ignite the gas reaction during the fusion of nanobubbles in water at room temperature. Therefore, the nanobubble-based gas-gas reactions provide a safe and efficient pathway to produce energy and synthesize new matter inaccessible under mild or ambient conditions.