ChemPhysChem

The relative reactivity and cis/trans selectivity of the intramolecular [3+2] cycloaddition (IM32CA) reactions of nitrile oxide (NO), azide (AZ), nitrile sulfide (NS) and nitrile ylide (NY), leading to functionalized heterocycles are studied within the Molecular Electron Density Theory. The kinetically controlled IM32CA reactions are predicted to be cis stereospecific, while the reaction feasibility follows the order NY>NS>NO>AZ with the respective activation Gibbs free energies of 13.7, 17.8, 21.1 and 27.3 kcal ⋅ mol⁻¹ in benzene at 353 K. The decreased activation energy of NY could be correlated with its carbenoid character, relative to the zwitterionic one predicted for the other three species. The AZ reaction showed relatively higher activation parameter, and accordingly higher than that of the NO one, in conformity with the experimental outcomes. Topological analysis of the electronic structure of the transition state structure shows that the formation of the new single bonds has not yet started on any of them according to a non‐concerted mechanism. Analysis of the kinetic parameters of the intermolecular [3+2] cycloaddition reactions of NOs and AZs shows that the low activation entropies associated with the intramolecular processes are the factor responsible for the feasibility of these non‐polar zw‐type IM32CA reactions.

Undesirable loss of open‐circuit voltage and current of metal halide perovskite (MHP) solar cells are closely associated with defects, so theoretical calculations have been often performed to scrutinize the nature of defects in bulk of MHPs. Yet, exploring the properties of defects at surfaces of MHPs is severely lacking given the complexity of the surface defects with high concentrations. In this study, IPb (PbI) antisite defects, namely one Pb (I) site being occupied by one I (Pb) atom at the surfaces of the FAPbI3 (FA=CH(NH2)2) material, are found to create electron (hole) traps when the surfaces with IPb (PbI) antisite defects are negatively (positively) charged. These are in sharp contrast to the conventional viewpoint that electron (hole) traps are induced by positively (negatively) charged defects. The reasons are discovered through Bader charge analysis, suggesting that there is deficient (excessive) electron charge in the vicinity of the IPb (PbI) defects with respect to the case in pristine surface of FAPbI3 material. Such understanding is then used as guidelines for effectively healing the anomalous IPb (PbI) antisite defects according to Lewis acid‐base chemistry, which is exampled by passivating theophylline (C60) molecules on defective surfaces of the FAPbI3 material.

Zinc tin oxide (ZTO) is investigated as a photoluminescent sensor for oxygen (O2); chemisorbed oxygen quenches the luminescence intensity. At the same time, ZTO is also studied as a resistive sensor; being an n‐type semiconductor, its electrical conductance decreases by adsorption of oxygen. Both phenomena can be exploited for quantitative O2 sensing. The respective sensor responses can be described by the same modified Stern‐Volmer model that distinguishes between accessible and non‐accessible luminescence centers or charge carriers, respectively. The impact of the temperature is studied in the range from room temperature up to 150 °C.

Anode free concepts are gaining traction in battery research. To improve cyclability, a better understanding of the deposition processes and morphologies is necessary. Correlative experiments enable a link between a variety of properties obtained, such as chemical, mechanical or electrochemical data. Here, electron paramagnetic resonance imaging (EPRI) is correlated with atomic force microscopy (AFM) to gain a deeper understanding of the microscopic topography and local stiffness at different intensities of the lithium selective EPRI map. Experiments were carried out on a sample of lithium deposited on copper foil from standard battery electrolyte. The correlation of both methods reveals that EPRI has a high sensitivity towards small lithium structures, while bulk lithium was not detected. The results demonstrate that EPRI can be used for prescreening to identify regions with different properties, which can then be analysed individually by AFM.

High entropy alloy (HEA) nanoparticles (NPs) have attracted much attention recently due to their unprecedented chemical properties. As such, HEA NPs have been used as materials with superior activity toward electrocatalytic applications. Specifically, solid solutions that form randomly mixed single‐phased structures have received the most focus in the early stages of HEA NP development for their entropic‐driven design and multifunctionality. Advances to non‐colloidal and colloidal synthetic methods have allowed for the fabrication of solid solution HEA NPs with varying compositions and complexity to be applied to many practical applications such as fuel cells, energy storage and agriculture. In this review, the current colloidal methods and catalytic mechanisms for solid solution HEA NP synthesis are investigated from the physical chemistry perspective. A comprehensive discussion on the theory, techniques, and electrocatalytic applications of colloidal syntheses for successful solid solution HEA NP formation is presented. Finally, promising perspectives for the continued development of physical insights into structure‐property relationships towards improved HEA NP synthesis and application are discussed.

For batteries to function effectively all active material must be accessible requiring both electron and ion transport to each particle. A common approach to generating the needed conductive network is the addition of carbon to create a composite electrode. An alternative approach is the electrochemically induced formation of conductive reaction products where the electrochemically generated materials are in intimate contact with the active material contributing to effective connection of each active particle. This study probes silver vanadium oxide (Ag2V4O11, SVO), carbon monofluoride (CFx), and hybrid SVO/CFx electrodes in lithium batteries. Ex situ XRD identifies Ag⁰ as a reduction product from SVO and LiF from CFx that can be followed as a function of depth‐of‐discharge (DOD). Spatially‐resolved operando energy dispersive x‐ray diffraction reveals that the presence of SVO alleviates reaction heterogeneity in the electrodes which are electron transfer limited in the absence of sufficient Ag⁰. Synchrotron X‐ray tomography on discharged cathodes reveals the distribution of silver particles where the particles are more closely spaced near the current collector indicating multiple nucleation sites for their formation. Finally, operando isothermal microcalorimetry is used to determine the heat dissipation of the parent and hybrid battery types. Using material enthalpy potentials, we determine the current distribution between the two active materials for the discharging hybrid cathode adding further insight to the diffraction analysis. Taken together, these results provide a comprehensive understanding of hybrid SVO/CFx cathodes and give guidance on optimal compositions that balance power and energy density considerations.

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 efficient CEST build‐up (depolarization rate), spectral resolution (line width), and subsequent effects like changes in chemical shifts of CEST responses must be considered, too. 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 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) methods, 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.

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.

The orthorhombic structure of FeNbO4, where the Fe and Nb cations are distributed randomly over the octahedral 4c sites, has shown excellent promise as an anode material in solid oxide fuel cells. We have used DFT+U‐D2 calculations to explore the adsorption and dissociation of H2 molecules and the formation reaction of water at the (010) and (111) surfaces. Simulations of the surface properties confirmed that the bandgaps are significantly reduced compared to the bulk material. We found that the hydrogen molecule prefers to dissociate at the O bridge sites of the (010) and (111) surfaces, especially where these are coordinated to Fe cations, thereby forming two hydroxyl groups. We have investigated the water formation reaction and found that the energy barriers for migration of the H ions are generally lower for the Fe/Nb‐O sites than for the O‐O site. Overall, our simulations predict that after dissociation, the H atoms tend to remain stable in the form of Olayer‐H groups, whereas a larger barrier needs to be overcome to achieve the formation of water. Future work will focus on potential surface modifications to reduce further the barrier of migration of the dissociated H ions, especially from the oxygen bridge sites.

This study investigates the modulations in the optical properties of cationic surfactant cetylpyridinium chloride (CPC) and hydrazine‐mediated copper nanoclusters (CuNCs). By employing a bottom‐up approach, we demonstrate the formation of blue‐emitting CuNCs facilitated by CPC and hydrazine, where hydrazine acts both as a reducing and stabilizing agent. The optical properties of the CuNCs were systematically tuned by varying the chain length of the diamine, resulting in emissions ranging from blue to yellow. Comprehensive characterization using spectroscopic and microscopic techniques confirmed the successful formation of CuNCs and elucidated the roles of CPC and hydrazine in their preparation. Control experiments highlighted the critical role of the pyridinium moiety and hydrophobic chain of CPC in enhancing the photoluminescence properties of the CuNCs. This work provides new insights into the design of stable, highly luminescent CuNCs for potential applications in optoelectronics and bioimaging.

Biophysical studies in the last two decades have clearly demonstrated that salts affect biomolecules in an ion‐specific manner (i. e., Hofmeister Effects). Studies performed upon such diverse biological processes such as protein folding, protein precipitation, protein coacervation and phase separation, and protein oligomerization, have all shown that this ion specificity is directly related to how individual ions interact with biomolecular surfaces. Interestingly, although ion‐specific effects upon enzyme catalytic processes are well‐known in the literature, a molecular level description of these effects has not yet been made available. For example, it is not clear whether ion‐specific effects observed in enzyme catalysis are directly related to how ions modulate the enzyme's folding free energy, or not. This work attempts to address this need by investigating ion‐specific effects upon the enzymatic activity and folding free energy of a well‐characterized enzyme system, Ribonuclease A (RNase A). To this end we have developed a robust framework to analyze and quantify ion‐specific effects upon the RNase A catalyzed phosphate ring opening reaction of cCMP (Cytidine 2′:3′‐cyclic monophosphate monosodium salt). Our studies show that both the folding thermodynamics and the Michaelis‐Menten kinetic parameters of this enzyme show ion‐specific salt dependence. However, even through salt addition affects the folding free energy and enzyme catalysis of RNase A in an ion‐specific manner, these effects are not necessarily directly related to each other. Ion‐specific effects observed in protein folding reflects mostly how an individual ion interacts with the overall protein surface; while alternatively, ion‐specific effects on enzyme activity indicate how a given ion interacts with the enzyme active site surface or alternatively, how ions interact with the substrate molecule as represented by changes in the substrate thermodynamic activity coefficient.

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.

Covalent bonding and noncovalent interactions are important chemical concepts and how to identify them has been of current interest in the literature. Within the framework of density functional theory (DFT), we recently proposed a few qualitative descriptors to categorize different types of interactions with Pauli energy and its derivatives. In this work, we expand the scope by including the quantities derived from energetic information, which were recently proposed and thoroughly investigated by us from the framework of information‐theoretic approach (ITA) in DFT. To that end, six energetic information quantities stemmed from the steric energy (Es), including Shannon entropy [[EQUATION]], Fisher information [[EQUATION]], information gain [[EQUATION]], alternative Fisher information [[EQUATION]], relative Fisher information [[EQUATION]], and relative alternative Fisher information [[EQUATION]] are examined for the purpose. A strong linear correlation of Es or its topological analysis results with different covalent bond orders is established. We also unveil that signature isosurfaces of different categories of interactions from [[EQUATION]] and [[EQUATION]] can be employed to simultaneously identify single, double, triple, and quadruple covalent bonds, ionic and metallic bonds, and van der Waals interactions. This work provides another pathway for us to use density‐based quantities to simultaneously identify covalent and noncovalent interactions.

Understanding the reversible transformation between two isomeric states of organic molecules under external stimulation is essential for advancing single‐molecule device development. Photochromic diarylethene (DAE) derivatives are promising candidates for single molecular switching elements. This study investigates the single‐molecule reactions of the closed‐form isomer of a DAE derivative on Cu(111) using scanning tunneling microscopy (STM). A novel ring‐opening pathway, distinct from the well‐known photochromic isomerization, was discovered. Electron injection into the lowest unoccupied molecular orbitals induces the sequential anchoring of molecules to the substrate through the dehydrogenation of a methyl group at the 2‐position of the thiophene ring. This mechanism was revealed by density functional theory calculations and STM simulations. The adsorption configurations for singly and doubly dehydrogenated DAEs were identified. Based on these findings, a new reaction mechanism extending beyond reversible isomeric reactions is proposed for DAE on Cu(111). The present work establishes a novel framework for future studies on single‐molecule switching phenomena on metal substrates.

To improve bioavailability, enhance the solubility and stability of the hydrophobic drug curcumin, nanoparticles such as carbon quantum dots (CQDs) are unique choices. In this study, we present a simple, cost‐effective, and eco‐friendly method for synthesizing nitrogen‐doped carbon quantum dots (N‐CQDs) and their application in the efficient delivery of hydrophobic drugs curcumin into live cancer cells. The N‐CQDs produced in this study exhibit excellent water solubility, remarkable stability, and high biocompatibility. To synthesize the N‐CQD, we use a carbon source found naturally (lemon juice) and for doping, we use N‐rich doping agents such as ethylene diamine and urea by using eco‐friendly chemical oxidation methods. The resulting N‐CQDs, with particle sizes under 10 nm, exhibit a good quantum yield, reinforcing their utility for biomedical applications. N‐CQDs and drug‐loaded particles are evaluated using various techniques like UV‐Vis, Fluorescence Spectroscopy, Dynamic Light Scattering (DLS), and Atomic Force Microscopy (AFM) as well. Additionally, we report a remarkable method to use N‐CQDs as carriers for the anticancer drug curcumin, significantly enhancing the solubility in live cells. Our research also delved into the application of N‐CQDs in in vivo bioimaging and drug release studies within live cancer cells, with a particular focus on their pH‐dependence behavior.

The [4+2] Diels‐Alder cycloaddition reaction between 2,5‐DMF (1) and ethylene derivatives (2a‐h) activated by electron‐withdrawing groups has been studied at the density functional theory levels using a panoply of tools to unravel the reaction mechanisms. From the analysis of the reactivity indices, 2a‐h behave as electrophiles while 1 as nucleophile, and the activation of the double bond of ethylene increases its electrophilicity, which is accompanied by an enhancement of the polarity of the reaction. The activation Gibbs free energy decreases linearly as a function of this increase of polarity, as estimated by the electrophilicity difference between the reactants. The difference of electrophilicity drives also the global electron density transfer at the transition state and the asynchronicity of the reaction, as evaluated by the difference of carbon‐carbon bond lengths in the transition state. Then, Bonding Evolution Theory shows that the activation of the double bond of ethylene by an electron‐withdrawing group changes the reaction mechanism from a one‐step synchronous process to a one‐step asynchronous process. Generally, the endo pathway is kinetically favored but, thermodynamically, it is the exo pathway. Finally, using the Distortion/Interaction‐Activation Strain, it is shown that the endo/exo selectivity is mostly driven by the differences of interaction energies.

The light‐sensing activity of phytochromes is based on the reversible light‐induced switching between two isomerization states of the bilin chromophore. These photo‐transformations may not necessarily be only unidirectional, but could potentially branch back to the initial ground state in a thermally driven process termed shunt. Such shunts have been rarely reported, and thus our understanding of this process and its governing factors are limited. Here, we aim to close this gap by providing coherent experimental evidence of a shunt process using UV/Vis laser flash photolysis. We studied the Pfr to Pr dynamics of the single GAF domain (g1) construct of the knotless phytochrome All2699 from cyanobacterium Nostoc punctiforme. We identified a shunt that can be switched on and off by ambient buffer conditions. In combination with H/D exchange and kinetic modeling, we propose a keto‐enol tautomerism to allow for the thermal isomerization of the chromophore and act as the driver of the shunt transition.

Electrochemical reduction of nitrate to ammonia (NO3RR) offers a promising strategy for renewable ammonia (NH3) synthesis and wastewater treatment, but still suffers from limited activity and NH3 selectivity due to the lack of effective electrocatalyst. Here, we perform a four‐steps screening strategy to screen high performance NO3RR catalyst by density functional theory calculations using 23 single transition metals atom doped on 1T‐WS2/graphene (TM@1T‐WS2/graphene) as candidates. The results show that Cu@1T‐WS2/graphene exhibits the highest NO3RR performance among 23 candidates with a low rate determining step energy barrier of 0.12 eV, which is much lower than that of the most of recently reported NO3RR catalysts. Moreover, the Cu@1T‐WS2/graphene also possesses excellent NH3 selectivity by suppressing competing hydrogen evolution reaction. This work provides a new avenue for the design of effective electrocatalysts for NO3RR.

With a view towards the development of molecular spintronics, non‐linear optics, and qubits, a great amount of research effort aims to establish the factors which govern the spin classification of diradicals. Electron spin resonance (ESR) is an indispensable tool for such research. However, in some cases, the mere presence of an ESR spectrum is insufficient to ascertain that the presumed diradical is indeed a triplet state. In a comparative case study of a Chichibabin diradical and a monoradical analogue, we show how the signals from different spin states present in liquid solutions of these species may be disentangled. Ultimately, the correct spin classification depends on ESR techniques which probe the spin quantum number directly. In this work, electron nuclear double resonance experiments reveal that the nuclei provide a clear experimental probe of the electronic spin configuration.

With the rapid advancement of information technology, the need to achieve ultra‐high‐density data storage has become a pressing necessity. This study synthesized three hyperbranched polyimides (HBPI‐TAPP, HBPI‐(Zn)TAPP, and HBPI‐(Cu)TAPP) by polymerizing 5,10,15,20‐tetrakis(4‐aminophenyl)porphyrin (TAPP), which features a cavity for metal ion coordination, with 4,4'‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), to systematically investigate the effect of metal ion species on storage performance. According to the results, memory devices based on HBPI‐(Zn)TAPP exhibit volatile SRAM (static random‐access memory) characteristics, whereas devices employing HBPI‐TAPP and HBPI‐(Cu)TAPP demonstrate non‐volatile WORM (write‐once, read‐many) characteristics. Molecular simulations based on density functional theory (DFT) reveal that the storage behaviors of these polymers are governed by a charge‐transfer mechanism, wherein electrons transfer from the porphyrin donor segment to the 6FDA acceptor segment, forming charge‐transfer complexes that are not easily dissociated. The larger dipole moments of HBPI‐TAPP and HBPI‐(Cu)TAPP render the complexes difficult to dissociate, resulting in WORM‐type memory behavior. In contrast, HBPI‐(Zn)TAPP has the lowest threshold voltage, with a stronger electron binding that hinders the dissociation of the charge transfer complex, thereby enabling SRAM‐type memory behavior.