Chemphyschem最新文献

Electric double layer capacitors (EDLC) require large specific surface area to provide high power density. The generation of pores increases the electrochemical capacitance with more graphitic edge planes exposed to the electrolyte. Conventional theory believes this increasing in capacitance is owed to the increased specific surface area, but our work uncovers another mechanism. DFT calculations discover the commonly seen defect-free zigzag and armchair edges can increase the quantum capacitance (C_Q) due to their high chemical activity. Meanwhile, high chemical activity makes defect-free edges interact with electrolyte molecules more easily, leading to the potential reduce of electrolyte stabilization and the change on the origin mechanism of double layer capacitance (C_D). Additionally, edges with non-hexagonal defects show a better balance between high C_Q and electrolyte stability. Therefore, our discovery proves the preservation of non-hexagonal defects in edge planes through possible temperature controlling in heat treatment is important in reaching high electrochemical properties for EDLC.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials possess unique advantages of high-efficiency and narrowband emission, which have rapidly occupied an important position in the field of organic light-emitting diodes (OLEDs). In recent years, significant advancements have been made in the development of MR-TADF materials, particularly in achieving spectral narrowing for high-color-purity OLED applications. Based on diverse MR-TADF molecular skeletons, this review summarizes the primary molecular strategies to narrow spectrum by suppressing structural relaxation and intermolecular interactions. Key strategies include π-conjugation extension, increased molecular rigidity, and the introduction of bulky substituents and intramolecular hydrogen bonds. Additionally, effects of these strategies on photophysical properties are discussed. These molecular design strategies are expected to offer valuable insights for the future design of high-efficiency, narrowband OLED emitters.

Delocalized multicenter bonds play a crucial role in clusters with a planar hypercoordinate center(s), making it difficult for highly electronegative elements, especially halogen atoms, to achieve the planar hypercoordinate arrangement. Herein, we introduce a star-like cluster Br6Li5-, whose global minimum contains a planar pentacoordinate bromine (ppBr). In this cluster, the central ppBr atom coordinates with five alkali metal Li atoms, which in turn bridge an equal number of electronegative Br atoms in the periphery, leading to the formation of the binary cluster Br6Li5-. Remarkably, bonding analyses indicate that the planar pentacoordinate configuration of Br6Li5- is dominated by the electrostatic interactions between the central ppBr atom and the Li5Br5 framework rather than covalent interactions. Despite the absence of delocalized bonds, Br6Li5- is still a highly stable cluster with a wider HOMO-LUMO gap of 7.73 eV and a higher VDE of 7.55 eV. Therefore, Br6Li5- should be a promising candidate for future gas-phase generation and spectroscopic characterization.

The aromaticity of a representative sample of pro-aromatic radicals and its nitro, amino, hydroxyl and imine substituted derivatives has been analysed by means of multicenter delocalization indices (MCI) and nuclear-independent chemical shifts (NICS). Because of their radical character, these compounds may exhibit conflicting α/β aromaticity, so that the contribution of α and β electrons to the MCI and NICS has been analysed separately and their values qualitatively interpreted in terms of the 2n+1/2n rule. All the monocyclic radicals investigated show conflicting α/β aromaticity. Thus, significant MCI values have been found for one of the spin components, whereas negligible values, even slightly negative, have been obtained for the other spin component. NICS indices confirm the aromatic character reflected by the MCIs and clearly show the antiaromatic or non-aromatic character of the other spin components. The same has been found for the donor rings of the bicyclic pro-aromatic radicals investigated, whereas all the fused benzene rings of these radicals show a clear aromatic character in both spin components. Substitutions at the donor carbon position by strong deactivating groups provoke a small increase of the aromatic character in the aromatic spin components and a significant decrease of the antiaromatic character in the antiaromatic spin components whereas activating groups have little effect.

Chemical exchange saturation transfer (CEST) improves the sensitivity of NMR but depending on the spin exchange kinetics, it can require substantial RF energy deposition to label magnetization. Potential side effects like RF-induced heating may occur and must be monitored. Here, we explore the parameter space considering not only undesired heating but also efficient CEST build-up (depolarization rate), spectral resolution (line width), and subsequent effects like changes in chemical shifts of CEST responses. We present a systematic study to compare conventional block pulse with shaped-pulse saturation and quantify how the effective average saturation power impacts these parameters. Pulse shape and nominal excitation bandwidth, however, turned out to have little impact on acquired z-spectra and temperature changes. This study illustrates how different exchange kinetics define different regimes of suitable RF power within the dynamic range of fully saturable magnetization from hyperpolarized ¹²⁹Xe. Temperature-related changes in the resonance frequency of bound spins were also quantified for the two Xe hosts CB6 and CrA-ma and put into context for typically used CEST acquisition parameters, including the stability of the magnetic field.

Aggregation-caused quenching (ACQ) reduces luminescence and compromises brightness in solid-state displays, necessitating strategies to mitigate its effects for enhanced performance. This study presents cost-effective method to mitigate ACQ of pyrene by co-assembling polycyclic aromatic hydrocarbons within low molecular weight gelator. Synthesized from readily available materials - cholesteryl chloroformate and pentaerythritol - in one-step reaction, gelator incorporates four cholesteryl units, reported to promote robust supramolecular gels in various solvents. Encapsulation of pyrene in a supramolecular host has effectively addressed the challenge of ACQ in the solid-state. Utilizing steady-state and time-resolved spectroscopic techniques, we probed the excimer formation dynamics across solution, powder, and xerogel phases. Through time-resolved emission spectra (TRES) and time-resolved area-normalized emission spectra (TRANES), we observed the monomer-to-excimer transition under various conditions. In solution, this transition occurs in a single step, characterized by a single isoemissive point (~443 nm) observed in TRANES. In powder, two isoemissive points (~445 nm and ~485 nm) were observed, indicating more complex process with an additional relaxed or trap state. The xerogel phase revealed an intricate excimer formation pathway, involving three isoemissive points (~418 nm, ~442 nm, and ~423 nm). These observations suggest multiple intermediate states in monomer-excimer transition and distinct dynamics in the solid matrix.

The Cover Feature shows the space-confined CVD growth of high-quality MoS₂ monolayers. The Research Article by T. Jurca and co-workers (DOI: 10.1002/cphc.202400854) describes the use of a nickel foam monolith preloaded with microstructured MoO_x as the Mo source for the CVD process. By incorporation of a porous barrier and an inherently low loading of Mo source directly aligned with the substrate, this method ensures a dampened rate of delivery of both Mo and S to the substrate, leading to coverage of large, high-quality, mono-to-few layer triangular domains.

The Front Cover shows archaeological nails, which are used as substrates for combining Mott–Schottky and the voltammetry of immobilized particles in a study of metal corrosion. More information can be found in the Research Article by A. Doménech-Carbó and co-workers (DOI: 10.1002/cphc.202400805).

Electron delocalization is studied in the ground singlet and first excited triplet states of azulene-containing helicenes. After showing that the compounds we study can be synthesized, we show that they exhibit a charge separation in the ground state, which does not appear in their triplet excited state. Then, magnetically induced properties (IMS3D and ACID) and electron density decomposition methods (EDDB) are used to rationalize aromaticity in these systems. For azulene-based helicenes larger than a critical size, that is, for more than six fused cycles, unexpected aromatic delocalization circuits appear. This feature is understood via the decomposition of the wavefunction on sets of carefully chosen local electronic structures and fragment orbital diagrams.

Pentalene (C8H6) and NN- and BB-bridged heterocyclic analogues (BN)4H6, derived by replacement of CC pairs with BN, are taken as  paradigms for tuning of ring-current (anti)aromaticity by variation of π charge, electronegativity and substitution pattern.  Ab initio calculation of maps for the π current density induced in these model systems by a perpendicular external magnetic field exhibits the full range of tropicity, from diatropic aromatic to nonaromatic to paratropic antiaromatic, with a ready rationalisation in terms of an orbital model.  Further calculations on systems of varying charge in which these motifs are embedded in extended PAH systems with naphthalene and phenanthrene 'clamps' show promise for switching between current patterns and related  opto-electronic properties. Particular sensitivity to charge is found for the experimentally accessible NN-bridged heteropentalene hybrids.