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Zhili Wang, Weifeng Chu, Zhenchao Zhao, Zhengmao Liu, Hongyu Chen, Dong Xiao, Ke Gong, Fan Li, Xiujie Li,
The Journal of Physical Chemistry Letters pp 9398-9406; https://doi.org/10.1021/acs.jpclett.1c01448

Abstract:
Organic and inorganic structure-directing agents (SDAs) impact Al distributions in zeolite, but the insights into how SDAs manipulate Al distribution have not been elucidated yet. Herein, the roles of different SDAs such as cyclohexylamine (CHA), hexamethylenimine (HMI), and Na+ in selective Al substitution of MCM-49 zeolite are investigated comprehensively by multinuclear solid-state NMR. The results demonstrate that MCM-49 synthesized with HMI shows relatively more T6 and T7 Al, while more T2 Al is observed using CHA. The formation of T2 Al in both MCM-49(HMI) and MCM-49(CHA) is derived from Na+, while protonated HMIs show bias in incorporation of T6 and T7 Al. Most HMIs are occluded in protonated status, and about half of CHAs are occluded in nonprotonated status. The close spatial proximity between nonprotonated CHAs and Na+ synergistically promotes the formation of zeolite structure, leading to more Na+ ions occluded in the zeolite channel with preferential T2 Al substitution.
Keitaro Eguchi,
The Journal of Physical Chemistry Letters pp 9407-9412; https://doi.org/10.1021/acs.jpclett.1c02723

Abstract:
The ionization energy (IE) of pentacene in two- and three-dimensional (2D and 3D) thin films and its evolution with coverage were studied via photoelectron yield spectroscopy in ambient conditions. In the 2D thin films, the IE of pentacene was found to be nearly constant at 4.91 eV, irrespective of its island size, for an average island size exceeding 1.6 × 104 nm2. In the 3D thin films, however, a reduction in IE by 0.04 eV was clearly observed upon stacking an additional molecular layer on top of the monolayer film, and the IE decreased to 4.73 eV at 20 monolayers. These experimental findings demonstrate the IE evolution in the buried layers of the 3D thin films and the significant impact of the neighboring molecular layers on the IE in layered systems with molecular aggregation.
Chunhua Ying, , ,
The Journal of Physical Chemistry Letters pp 9429-9435; https://doi.org/10.1021/acs.jpclett.1c02412

Abstract:
Decoupling the ion motion and segmental relaxation is significant for developing advanced solid polymer electrolytes with high ionic conductivity and high mechanical properties. Our previous work proposed a decoupled ion transport in a novel protein-based solid electrolyte. Herein, we investigate the detailed ion interaction/transport mechanisms through first-principles density functional theory (DFT) calculations in a vacuum space. Specifically, we study the important roles of charged amino acids from proteins. Our results show that the charged amino acids (i.e., Arg and Lys) can strongly lock anions (ClO4–). When locked at a proper position (determined from the molecular structure of amino acids), the anions can provide additional hopping sites and facilitate Li+ transport. The findings are supported from our experiments of two protein solid electrolytes, in which the soy protein (with plenty of charged amino acids) electrolyte shows much higher ionic conductivity and lower activation energy in comparison to the zein (lack of charged amino acids) electrolyte.
Kai Hu, Li-Min Guan, , Fuyang Liu,
The Journal of Physical Chemistry Letters pp 9422-9428; https://doi.org/10.1021/acs.jpclett.1c02308

Abstract:
In the areas of condensed matter physics, geoscience, material science, and inorganic chemistry, how the crystal structures evolve under an external field such as high-pressure is a fundamental question. By taking TiSe2 as the case, we investigate the phase transformations of the layered transition-metal dichalcogenides (TMDs) under high-pressure. The ambient 6-fold P-3m1 TiSe2 undergoes a transformation into the monoclinic 8-fold coordinated C2/m phase at 15 GPa and then into the hexagonal 9-fold Fe2P-type structure at 34 GPa. The above phase transitions can be unitedly described as the evolution of the vacancies: from a layered structure with two-dimensional (2D) vacancies to the structure with one-dimensional (1D) and zero-dimensional (0D) vacancies. The proposed densification model of TiSe2 reveals the processes how the symmetry breaking phase of spatial chemical bonding restores the symmetry under the isotropic external pressure.
, Marco Deiana, Kinga Szkaradek, Mikołaj J. Janicki, Ziemowit Pokładek, Robert W. Góra,
The Journal of Physical Chemistry Letters pp 9436-9441; https://doi.org/10.1021/acs.jpclett.1c02207

Abstract:
The design of artificially engineered chiral structures has received much attention, but the implementation of dynamic functions to modulate the chiroptical response of the systems is less explored. Here, we present a light-responsive G-quadruplex (G4)-based assembly in which chirality enrichment is induced, tuned, and fueled by molecular switches. In particular, the mirror-image dependence on photoactivated azo molecules, undergoing trans-to-cis isomerization, shows chiral recognition effects on the inherent flexibility and conformational diversity of DNA G4s having distinct handedness (right- and left-handed). Through a detailed experimental and computational analysis, we bring compelling evidence on the binding mode of the photochromes on G4s, and we rationalize the origin of the chirality effect that is associated with the complexation event.
Tingyu Lei, , , Sharan Shetty, Qingya Liu,
The Journal of Physical Chemistry Letters pp 9413-9421; https://doi.org/10.1021/acs.jpclett.1c02892

Abstract:
The in situ formation and removal of coke is a critical problem in heterogeneous catalysis, but its mechanism is not well understood. This work investigates the mechanism of carbon deposition and hydrogenation on an Fe cluster under high-temperature conditions with the density functional tight-binding (DFTB) based nanoreactor molecular dynamics (NMD) method. Our study shows that successive formation of carbon chains, rings, and fused rings occurred during the carbon deposition on Fe clusters. Hydrogenation of activated carbon happens through direct C–H coupling, while the hydrogenation of graphitic carbon involves hydrogenation of the edge carbon, ring-opening reaction, and dealkylation reaction. The main function of the Fe catalyst is to provide the active sites for H2 dissociation and dissociated H spillover, while its activity toward C–C bond breaking is limited. These results highlight the role of the DFTB-NMD method as an effective tool to investigate reaction mechanisms under operating conditions in heterogeneous catalysis.
, , Michele Parrinello
The Journal of Physical Chemistry Letters pp 9449-9454; https://doi.org/10.1021/acs.jpclett.1c02135

Abstract:
We present an approach that extends the theory of targeted free energy perturbation (TFEP) to calculate free energy differences and free energy surfaces at an accurate quantum mechanical level of theory from a cheaper reference potential. The convergence is accelerated by a mapping function that increases the overlap between the target and the reference distributions. Building on recent work, we show that this map can be learned with a normalizing flow neural network, without requiring simulations with the expensive target potential but only a small number of single-point calculations, and, crucially, avoiding the systematic error that was found previously. We validate the method by numerically evaluating the free energy difference in a system with a double-well potential and by describing the free energy landscape of a simple chemical reaction in the gas phase.
The Journal of Physical Chemistry Letters pp 9442-9448; https://doi.org/10.1021/acs.jpclett.1c02454

Abstract:
We employ the Holstein model for polarons to investigate the relationship among defects, topology, Coulomb trapping, and polaron delocalization in covalent organic frameworks (COFs). We find that intrasheet topological connectivity and π-column density can override disorder-induced deep traps and significantly enhance polaron migration by several orders of magnitude in good agreement with recent experimental observations. The combination of percolation networks and micropores makes trigonal COFs ideally suited for charge transport followed by kagome/tetragonal and hexagonal structures. By comparing the polaron spectral signatures and coherence numbers of large three-dimensional frameworks having a maximum of 180 coupled chromophores, we show that controlling nanoscale defects and the location of the counteranion is critical for the design of new COF-based materials yielding higher mobilities. Our analysis establishes design strategies for enhanced conductivity in COFs that can be readily generalized to other classes of conductive materials such as metal–organic frameworks and perovskites.
Golokesh Santra, Emmanouil Semidalas,
The Journal of Physical Chemistry Letters pp 9368-9376; https://doi.org/10.1021/acs.jpclett.1c02838

Abstract:
By adding a GLPT3 (third-order Görling-Levy perturbation theory, or KS-MP3) term E3 to the XYG7 form for a double hybrid, we are able to bring down WTMAD2 (weighted total mean absolute deviation) for the very large and chemically diverse GMTKN55 benchmark to an unprecedented 1.17 kcal/mol, competitive with much costlier composite wave function ab initio approaches. Intriguingly, (a) the introduction of E3 makes an empirical dispersion correction redundant; (b) generalized gradient approximation (GGA) or meta-GGA semilocal correlation functionals offer no advantage over the local density approximation (LDA) in this framework; (c) if a dispersion correction is retained, then simple Slater exchange leads to no significant loss in accuracy. It is possible to create a six-parameter functional with WTMAD2 = 1.42 that has no post-LDA density functional theory components and no dispersion correction in the final energy.
Sanford Ruhman
The Journal of Physical Chemistry Letters pp 9336-9343; https://doi.org/10.1021/acs.jpclett.1c02408

Abstract:
Absolute absorption changes in molecular flash photolysis experiments are routinely translated into molar extinction coefficients and oscillator strengths of reactive intermediates. These direct quantum chemical investigation and allow precise concentration readings in later experiments. In this Perspective we show how a similar approach can deliver crucial information for interpreting transient absorption spectra in colloidal semiconductor quantum dots. The intrinsic complexity of such samples stemming from the inhomogeneity of particle size, shape, and surface chemistry poses unique challenges to mechanistic assignment of ultrafast pump–probe measurements. We will describe applications of this approach to elucidate the photophysics of quantum confined nanocrystals made of various semiconducting materials. These case studies demonstrate how, faced with conflicting interpretations, it has pointed in the right direction in assessing single and multiple exciton generation and relaxation, in searches for ultrafast carrier trapping and scavenging, and in tests of band edge level structure and state degeneracies.
Kie Hankins, Venkateshkumar Prabhakaran, Sungun Wi, Vaithiyalingam Shutthanandan, , Swadipta Roy, Hui Wang, , Suntharampillai Thevuthasan, , et al.
The Journal of Physical Chemistry Letters pp 9360-9367; https://doi.org/10.1021/acs.jpclett.1c01930

Abstract:
Delineating intricate interactions between highly reactive Li-metal electrodes and the diverse constituents of battery electrolytes has been a long-standing scientific challenge in materials design for advanced energy storage devices. Here, we isolated lithium polysulfide anions (LiS4–) from an electrolyte solution based on their mass-to-charge ratio and deposited them on Li-metal electrodes under clean vacuum conditions using ion soft landing (ISL), a highly controlled interface preparation technique. The molecular level precision in the construction of these model interfaces with ISL, coupled with in situ X-ray photoelectron spectroscopy and ab initio theoretical calculations, allowed us to obtain unprecedented insight into the parasitic reactions of well-defined polysulfides on Li-metal electrodes. Our study revealed that the oxide-rich surface layer, which is amenable to direct electron exchange, drives multielectron sulfur oxidation (S0 → S6+) processes. Our results have substantial implications for the rational design of future Li–S batteries with improved efficiency and durability.
The Journal of Physical Chemistry Letters pp 9384-9390; https://doi.org/10.1021/acs.jpclett.1c02398

Abstract:
Interactions of biomolecules with inorganic oxide surfaces such as silica in aqueous solutions are of profound interest in various research fields, including chemistry, biotechnology, and medicine. While there is a general understanding of the dominating electrostatic interactions, the binding mechanism is still not fully understood. Here, chromatographic zonal elution and flow microcalorimetry experiments were combined with molecular dynamic simulations to describe the interaction of different capped amino acids with the silica surface. We demonstrate that ion pairing is the dominant electrostatic interaction. Surprisingly, the interaction strength is more dependent on the repulsive carboxy group than on the attracting amino group. These findings are essential for conducting experimental and simulative studies on amino acids when transferring the results to biomolecule–surface interactions.
Yuki Nagumo,
The Journal of Physical Chemistry Letters pp 9377-9383; https://doi.org/10.1021/acs.jpclett.1c02230

Abstract:
Characteristic features of magnetoplasmonic responses in higher-order multipolar (quadrupolar and octupolar) modes of Ag nanoparticles (from 90 to 200 nm in diameter) are demonstrated for the first time using magnetic circular dichroism (MCD) spectroscopy. In optical extinction spectra, with an increase in the size of the nanoparticles, the red shift of dipolar plasmon peaks and the appearance of higher-order multipolar resonances can reasonably be observed. Aside from the dipolar and quadrupolar modes, the octupolar plasmonic extinction is very weak and almost unresolved. In contrast, strikingly, MCD shows a very sharp and intense peak (or valley) for the octupolar resonance, meaning its unique properties with high sensitivity and enhanced spectral resolution. MCD responses assignable to the quadrupolar mode have a distinct derivative-like shape, which is different from those observed for Ag nanocubes and nanodecahedra in our previous studies. We then discuss this behavior from the viewpoint of size and/or polyhedral shape inhomogeneity.
James Langford, Xi Xu,
The Journal of Physical Chemistry Letters pp 9391-9397; https://doi.org/10.1021/acs.jpclett.1c02645

Abstract:
Plasmons, which are collective and coherent oscillations of charge carriers driven by an external field, play an important role in applications such as solar energy harvesting, sensing, and catalysis. Conventionally, plasmons are found in bulk and nanomaterials and can be described with classical electrodynamics. In recent years, plasmons have also been identified in molecules, and these molecules have been utilized to build plasmonic devices. As molecular plasmons can no longer be described by classical electrodynamics, a description using quantum mechanics is necessary. In this Letter, we develop a quantum metric to accurately and efficiently identify and quantify plasmons in molecules. A number, which we call the plasmon character index (PCI), can be calculated for each electronic excited state and describes the plasmonicity of the excitation. PCI is developed from the collective and coherent excitation picture in orbitals and shows excellent agreement with the predictions from scaled time-dependent density functional theory but is vastly more computationally efficient. Therefore, PCI can be a useful tool in identifying and quantifying plasmons and will inform the rational design of plasmonic molecules and nanoclusters.
The Journal of Physical Chemistry Letters pp 9328-9335; https://doi.org/10.1021/acs.jpclett.1c02929

Abstract:
Perovskite solar cells (PSCs) exhibit large, reversible, and bidirectional light-soaking effects (LSEs); however, these anomalous LSEs are poorly understood, limiting the stability engineering and commercialization. We present a unified defect theory for the LSEs in lead halide perovskites by reconciling their defect photochemistry, ionic migration, and carrier dynamics. We considered typical detrimental defects (IPb, Ii, VI) and observed that two atomic configurations were favored, where the carrier lifetime of one configuration was nearly 1 order of magnitude longer than that in the other. First-principles calculations showed that light illumination promotes ion-diffusion-assisted transitions from energetically stable configurations to metastable configurations, which are converted back to stable configurations in the dark. Fermi-level-dependent formation energies of stable/metastable configurations were used to rationalize contradictory experimental results of anomalous LSEs in PSCs observed in various studies, thus providing insights for minimizing the LSE to achieve high-performance stable PSCs.
Zi Yang, Kai Yang, Xiaofan Wei, , Rong Gao, Frieder Jäkle, , Yi Ren
The Journal of Physical Chemistry Letters pp 9308-9314; https://doi.org/10.1021/acs.jpclett.1c02668

Abstract:
Harvesting high-energy excited-state energy is still challenging in organic chromophores. An introduction of boron atoms along the short axis of the diazapentacene backbone induces multiple emission characteristics. Our studies reveal that the weak molecular orbital (MO) coupling of the S3–S1 transition is responsible for the slow internal conversion rates. Such MO coupling-regulated anti-Kasha emission is different from the large band gap-induced anti-Kasha emission character of classical azulene derivatives. Theoretical studies reveal that a strong MO coupling of the S3–S0 transition is responsible for the higher photoluminescence quantum yield of the anti-Kasha emission in a more polar solution (tetrahydrofuran: 11%; cyclohexane: 0%). Such an MO coupling factor is generally overlooked in anti-Kasha emitters reported previously. Furthermore, the multiple emission can be regulated by solvent polarity, solvent temperature, and fluoride anion binding. As a proof of concept of harvesting high-energy emission, the multiple emission character has allowed us to design single-molecule white-light-emitting materials.
J. A. Peters, , O. Bulgin, Y. He, , M. C. De Siena, ,
The Journal of Physical Chemistry Letters pp 9301-9307; https://doi.org/10.1021/acs.jpclett.1c02397

Abstract:
Excitons in Bridgman grown halide perovskite CsPbBr3 single crystals were examined using photoluminescence (PL) spectroscopy to determine the nature of the electronic states. The photoluminescence intensity was strongly temperature-dependent and depended upon the specific exciton band. At low temperatures intrinsic disorder and its related shallow below bandgap tail states determine the emission properties. Photoluminescence at low temperature revealed the presence of several strong bands at the band edge that is attributed to free or trapped/bound excitons. This PL emission results from strong electron–phonon coupling with an average phonon energy Eph of 6.5 and 27.4 meV for the emissions, comparable to that observed in other perovskites. The Huang–Rhys parameter S was calculated to be 3.81 and 1.51, indicating strong electron–phonon coupling. The interactions between electrons and phonons produce small polarons that tend to bind charge carriers and result in trapped/bound excitons. The transient photoluminescence response of each specific band was studied, and the results indicated a multiphonon recombination process. Average PL lifetimes of ∼17 ns for free excitons and ∼38 ns for trapped/bound excitons were determined. The observed edge states could be associated with native defects such as vacancies and interstitials, as well as twinning due to the cubic-to-tetragonal phase transition in CsPbBr3. Elimination of the trapping sites for binding excitons could lead to improved charge transport mobilities, carrier lifetimes, and detector properties in this system.
, Shunya Tanaka, Katsuki Tanaka, Mayu Takino, , , , Daichi Hirobe, ,
The Journal of Physical Chemistry Letters pp 9283-9292; https://doi.org/10.1021/acs.jpclett.1c02896

Abstract:
Heterohelicenes are potential materials in molecular electronics and optics because of their inherent chirality and various electronic properties originating from the introduced heteroatoms. In this work, we comprehensively investigated two kinds of double NO-hetero[5]helicenes composed of 12H-benzo[b]phenoxazine (BPO) and 13H-dibenzo[b,i]phenoxazine (DBPO). These helicenes exhibit good electron-donor properties reflecting the electron-rich character of their monomers and were demonstrated to work as p-type semiconductors. The enantiomers of these helicenes show the largest class of dissymmetry factors for circularly polarized luminescence (CPL) (|gCPL| > 10–2) among helicenes reported to date. Interestingly, the signs of CPL are opposite for BPO and DBPO double helicenes of the same helicity. The origin of the large gCPL values and the inversion of the CPL sign was addressed by analysis of the transition electronic dipole moments and transition magnetic dipole moments based on TD-DFT calculations.
Cheng Liu, Hongyi Chen, Wentao Deng, Jun Chen, Ye Tian, Xu Gao, Xinglan Deng, Shouyi Yi, Shuo Li, Libao Chen, et al.
The Journal of Physical Chemistry Letters pp 9321-9327; https://doi.org/10.1021/acs.jpclett.1c02248

Abstract:
The prospects of sodium (Na) metal batteries have been fatally plagued by interfacial Na dendrites, mainly affected by preferred nucleation on the metal anode and the steep gradient of Na ions in the electrolyte, leading to limited Coulombic efficiency and short lifespans. Herein, an electrochemically inert potassium-based Na–K alloy demonstrates a liquid alloying diffusion mechanism that enables dendrite-free Na anodes. The extremely small Na fluctuation and flexible Na–K bonds in the liquid alloy phase bring isotropic nucleation of Na upon electroplating/stripping, which is directly observed by in situ optical imaging. Spontaneously, serving as (de)sodiation buffer with faster electron/mass transportation, the liquid inertia also provides attenuated concentration distribution of Na. Significantly, a record capacity retention of approximately 100% is rendered when coupled with Na3V2(PO4)3 cathodes (ca. 2 mg cm–2) over 500 cycles at 10C, advancing the possibility of using liquid alloy for stable metal anodes beyond Na storage systems.
Jonghyuk Im, Kyungryun Lee, Sohyun Jung, Eunhee Kim,
The Journal of Physical Chemistry Letters pp 9315-9320; https://doi.org/10.1021/acs.jpclett.1c02605

Abstract:
Intrinsically disordered proteins (IDPs) play an important role in cell signaling, and NMR is well-suited to study conformational ensembles and dynamics of IDPs. However, the intrinsic flexibility of IDPs often results in severe spectral overlap, which hampers accurate NMR data analysis. By labeling the longitudinal spin order of an α proton (i.e., Hαz) on multiple quantum coherences of backbone nuclei (e.g., NyC′xCαy), we were able to apply pre-homonuclear decoupling (PHD) to transverse relaxation-optimized spectroscopy (TROSY). The proposed scheme provides ultrahigh resolution in both amide proton and nitrogen dimensions, as illustrated in the analysis of Tau and alpha-synuclein (α-Syn) proteins. The PHD-TROSY readout enabled complete backbone resonance assignment of α-Syn using a single 3D HNCA experiment performed on a 600 MHz NMR spectrometer.
Moon Young Yang, Soo-Kyung Kim, Donghwa Kim, ,
The Journal of Physical Chemistry Letters pp 9293-9300; https://doi.org/10.1021/acs.jpclett.1c02162

Abstract:
Bitter taste receptors (TAS2Rs) function in taste perception, but are also expressed in many extraoral tissues, presenting attractive therapeutic targets. TAS2R5s expressed on human airway smooth muscle cells can induce bronchodilation for treating asthma and other obstructive diseases. But TAS2R5s display low agonist affinity and the lack of a 3D structure has hindered efforts to design more active ligands. We report the structure of the activated TAS2R5 coupled to the Gi protein and bound to each of 19 agonists, using computational approaches. These agonists bind to two polar residues in TM3 that are unique for TAS2R5 among 25 TAS2R subtypes. Our predicted results correlate well with experimental results of agonist-receptor signaling coefficients, providing validation of the predicted structure. These results provide highly specific data on how agonists activate TAS2R5, how modifications of ligand structure alter receptor activation, and a guide to structure-based drug design.
The Journal of Physical Chemistry Letters pp 9239-9247; https://doi.org/10.1021/acs.jpclett.1c02209

Abstract:
Photophysical and photochemical processes are ruled by the interplay between transient vibrational and electronic degrees of freedom, which are ultimately determined by the multidimensional potential energy surfaces (PESs). Differences between ground and excited PESs are encoded in the relative intensities of resonant Raman bands, but they are experimentally challenging to access, requiring measurements at multiple wavelengths under identical conditions. Herein, we perform a two-color impulsive vibrational scattering experiment to launch nuclear wavepacket motions by an impulsive pump and record their coupling with a targeted excited-state potential by resonant Raman processes with a delayed probe, generating in a single measurement background-free vibrational spectra across the entire sample absorption. Building on the interference between the multiple pathways resonant with the excited-state manifold that generate the Raman signal, we show how to experimentally tune their relative phase by varying the probe chirp, decoding nuclear displacements along different normal modes and revealing the multidimensional PESs. Our results are validated against time-dependent density functional theory.
Saptarsi Mondal, Jooyoun Kang, Kwanghee Park, Jong Min Lim, Jeong-Hyon Ha, ,
The Journal of Physical Chemistry Letters pp 9275-9282; https://doi.org/10.1021/acs.jpclett.1c02491

Abstract:
The role of water in the excellent biocompatibility of the acrylate-based polymers widely used for antibiofouling coating material has been realized previously. Here, we report femtosecond mid-infrared pump–probe spectroscopy of the OD stretch band of HOD molecule adsorbed on highly biocompatible poly(2-methoxyethyl) acrylate [PMEA] and poorly biocompatible poly(2-phenoxyethyl) acrylate [PPEA], both of which reveal that there are two water species with significantly different vibrational lifetime. PMEA interacts more strongly with water than PPEA through the H-bonding interaction between carbonyl (C═O) and water. The vibrational lifetime of the OD stretch in PPEA is notably longer by factors of 3 and 7 than those in PMEA and bulk water, respectively. The IR-pump visible-probe photothermal imaging further unravels substantial spatial overlap between polymer CO group and water for hydrated PMEA and a significant difference in surface morphology than those in PPEA, which exhibits the underlying relationships among polymer–water interaction, surface morphology, and biocompatibility.
Ruo Xi Yang,
The Journal of Physical Chemistry Letters pp 9253-9261; https://doi.org/10.1021/acs.jpclett.1c02515

Abstract:
The stability of halide perovskites has been a long-standing issue for their real-world application. Approaches to improve stability include nanostructuring, dimensionality reduction, and strain engineering, where surfaces play an important role in the formation of a stable structure. To understand the mechanism we compute the lattice dynamics of the surface of CsPbI3 using density functional theory. We demonstrate, for the first time, that CsPbI3 crystals exhibit surface phonons that are localized on the outermost layers of the slabs, and we perform a complete symmetry characterization including an identification of the Raman/IR active modes. These surface phonons are present in the optically active cubic phase but are absent in the optically inactive “yellow” phase. Furthermore, we show that the surface suppresses bulk instabilities by hardening soft modes of the bulk cubic phase, resulting in phase stabilization and quenching of dynamical disorder. This study is fundamental for understanding the structural behavior of halide perovskite materials with high surface area-to-volume ratios, and for guiding stabilization strategies.
Valentina Wieser, , Robert D. Barker, Hsiu-Wei Cheng,
The Journal of Physical Chemistry Letters pp 9248-9252; https://doi.org/10.1021/acs.jpclett.1c02572

Abstract:
Lipid bilayer interactions are essential to a vast range of biological functions, such as intracellular transport mechanisms. Surface charging mediated by concentration dependent ion adsorption and desorption on lipid headgroups alters electric double layers as well as van der Waals and steric hydration forces of interacting bilayers. Here, we directly measure bilayer interactions during charge modulation in a symmetrically polarized electrochemical three-mirror interferometer surface forces apparatus. We quantify polarization and concentration dependent hydration and electric double layer forces due to cation adsorption/desorption. Our results demonstrate that exponential hydration layer interactions effectively describe surface potential dependent surface forces due to cation adsorption at high salt concentrations. Hence, electric double layers of lipid bilayers are exclusively dominated by inner Helmholtz charge regulation under physiological conditions. These results are important for rationalizing bilayer behavior under physiological conditions, where charge and concentration modulation may act as biological triggers for function and signaling.
Sijia Du, Suqian Ma, , Wenjing Tian
The Journal of Physical Chemistry Letters pp 9233-9238; https://doi.org/10.1021/acs.jpclett.1c02726

Abstract:
Organic cocrystals whose unique polymorphic feature can provide a feasible way to investigate and understand the relationship between luminescence properties and aggregate structures have attracted increasing attention in the area of organic optoelectronics. Herein, we prepare polymorphic cocrystals (C1, C2) by using 9,10-bis((E)-2-(pyridin-3-yl)vinyl)anthracene (BP3VA) as chromophore and 1,3,5-trifluoro-2,4,6-triiodobenzene (FIB) as conformer. Both C1 and C2 stack with segregated stacking form, but different intermolecular interactions promote the formation of sheet cocrystals C1 and needle cocrystals C2. C1 exhibits anisotropic optical waveguide property and photoluminescent polarization, while C2 only exhibits the quasi-one-dimensional optical waveguide property. The different optical properties originate from the varieties of molecular packing modes and directions of the optical transition dipole in the two polymorphic cocrystals, which can be clarified through the structure analysis and theoretical calculation. The study can provide a deep understanding of the structure–property relationship of cocrystals and benefit the rational design of novel functional materials.
Gui-Duo Jiang, Zi-Yu Li, Li-Hui Mou,
The Journal of Physical Chemistry Letters pp 9269-9274; https://doi.org/10.1021/acs.jpclett.1c02683

Abstract:
Inspired by the fact that the active centers of natural nitrogenases are polynuclear iron–sulfur clusters, the reactivity of isolated iron–sulfur clusters toward N2 has received considerable attention to gain fundamental insights into the activation of the N≡N triple bond. Herein, a series of gas-phase iron–sulfur cluster anions FexSy– (x = 1–8, y = 0–x) were prepared and their reactivities toward N2 were investigated systematically by mass spectrometry. Among the 44 investigated clusters, only Fe5S2– and Fe5S3– showed superior reactivity toward N2. Theoretical results revealed that N2 binds molecularly to the iron sites of Fe5S2,3– in a common end-on coordination mode with an unprecedented back-donation interaction from the localized d–d bonding orbitals of Fe–Fe sites to the π* antibonding orbitals of N2. This is the first example to disclose the significant contribution of the dual metal sites rather than the single metal atom to N2 adsorption in the prevalent end-on binding mode.
The Journal of Physical Chemistry Letters pp 9262-9268; https://doi.org/10.1021/acs.jpclett.1c02597

Abstract:
Ligand-protected metal clusters are employed in a great many applications that include notably energy conversion and biomedical uses. The interaction between the ligands and the metallic cores, mediated by an often complex interface, profoundly influences the properties of small clusters, in particular. Nonetheless, the mechanisms of interaction remain far from fully understood. The Au144L60 class of cluster compounds has long played a central role in the study of monolayer-protected clusters, but total structure determination has been achieved only recently for a thiolated and an all-alkynyl cluster. Both ligands contain aromatic rings but differ in their ligation to the metal core: conjugation along a triple bond in the latter, saturation in the former. We demonstrate the paramount importance of the conjugation in the connection between aromatic ligand rings and metal cores for the electronic and optical properties and, by extension, the critical transport properties, providing a crucial element for the development of design-principle-based synthesis.
Kirill Karpov, Artem Mitrofanov, , Valery Tkachenko
The Journal of Physical Chemistry Letters pp 9213-9219; https://doi.org/10.1021/acs.jpclett.1c02477

Abstract:
The use of machine learning in chemistry has become a common practice. At the same time, despite the success of modern machine learning methods, the lack of data limits their use. Using a transfer learning methodology can help solve this problem. This methodology assumes that a model built on a sufficient amount of data captures general features of the chemical compound structure on which it was trained and that the further reuse of these features on a data set with a lack of data will greatly improve the quality of the new model. In this paper, we develop this approach for small organic molecules, implementing transfer learning with graph convolutional neural networks. The paper shows a significant improvement in the performance of the models for target properties with a lack of data. The effects of the data set composition on the model’s quality and the applicability domain of the resulting models are also considered.
Matthew D. Hanson, Janel A. Readnour, ,
The Journal of Physical Chemistry Letters pp 9226-9232; https://doi.org/10.1021/acs.jpclett.1c02254

Abstract:
Spectroscopic studies of protonated water clusters (PWCs) have yielded enormous insights into the fundamental nature of the hydrated proton. Here, we introduce a new coupled local-mode (CLM) approach to calculate PWC OH stretch vibrational spectra. The CLM method combines a sampling of representative configurations from density functional theory (DFT)-based ab initio molecular dynamics (AIMD) simulations with DFT calculations of local-mode vibrational frequencies and couplings. Calculations of inhomogeneous OH stretch vibrational spectra for H+(H2O)4 and H+(H2O)21 agree well with experiment and higher-level calculations, and decompositions of the calculated spectra in terms of the coupled modes aids in the interpretation of the spectra. This observation is consistent with the idea that capturing anharmonicity and coupling is as important to accuracy as the underlying level of electronic structure theory. The CLM calculations can easily discern the configuration that dominates the experimental measurement for H+(H2O)5, which can adopt several low-energy conformations.
Robert Stanton, Emma Russell, Hayden Brandt, Dhara J. Trivedi
The Journal of Physical Chemistry Letters pp 9175-9181; https://doi.org/10.1021/acs.jpclett.1c02550

Abstract:
The effective capture of common water contaminants using metal–organic frameworks (MOFs) presents a remedy for current environmental concerns arising from the pollution of water sources. The crystalline porous nature of MOFs, their high internal surface area, and exceptional tunability make them suitable candidates for sequestration and removal of pollutants. However, the efficiency of capture depends largely on the nature of the interactions between the anions and the MOF. In this work, to elucidate the host–guest interactions involved in the capture of such pollutants, we explore three characteristically different MOFs: ZIF-8, iMOF-2c, and MOF-74. We demonstrate by ab initio electronic structure calculations the importance of exploiting qualitatively different binding modes for strong host–guest interactions available in the selected MOFs. Our simulations reveal the relative performance of neutral and cationic adsorbents while underscoring the importance of employing MOFs containing open metal sites for the efficient uptake of anions.
, Francesco Tavani, Silvia Mauri, , Damjan Krizmancic, Alessandro Tofoni, Valentina Colombo, , Piero Torelli
The Journal of Physical Chemistry Letters pp 9182-9187; https://doi.org/10.1021/acs.jpclett.1c02585

Abstract:
In this work, we apply for the first time ambient pressure operando soft X-ray absorption spectroscopy (XAS) to investigate the location, structural properties, and reactivity of the defective sites present in the prototypical metal–organic framework HKUST-1. We obtained direct evidence that Cu+ defective sites form upon temperature treatment of the powdered form of HKUST-1 at 160 °C and that they are largely distributed on the material surface. Further, a thorough structural characterization of the Cu+/Cu2+ dimeric complexes arising from the temperature-induced dehydration/decarboxylation of the pristine Cu2+/Cu2+ paddlewheel units is reported. In addition to characterizing the surface defects, we demonstrate that CO2 may be reversibly adsorbed and desorbed from the surface defective Cu+/Cu2+ sites. These findings show that ambient pressure soft-XAS, combined with state-of-the-art theoretical calculations, allowed us to shed light on the mechanism involving the decarboxylation of the paddlewheel units on the surface to yield Cu+/Cu2+ complexes and their reversible restoration upon exposure to gaseous CO2.
, Hao Hu, Weiwei Liu, Yanying Wang, ,
The Journal of Physical Chemistry Letters pp 9205-9212; https://doi.org/10.1021/acs.jpclett.1c02809

Abstract:
Triplet exciton formation is essential for photosensitization-based photochemistry and photobiology. The heavy atom effect (HAE), in the form of either external or internal mode, is a basic mechanism for increasing the triplet exciton yield of photosensitizers. Herein, we report a new HAE mode by noncovalent cohosting of heavy atoms and photosensitizers in a double-stranded DNA (dsDNA) matrix. With dsDNA bearing several thymine (T) or cytosine (C) mismatches, heavy atoms (e.g., Hg2+ or Ag+) and dsDNA-staining dyes (photosensitizers) were spatially adjoined in close proximity, thus resulting in enhanced phosphorescence and 1O2 generation from the photosensitizers. The dsDNA-hosted HAE provides highly selective recognition for the heavy atoms, which is not applicable in either the external or the internal mode. Considering the simpleness and efficiency of the spatially adjoined HAE, as well as the functionality of DNA, the proposed HAE mode is appealing for various singlet oxygen- and phosphorescence-related applications.
Max D. J. Waters, Wenpeng Du, Andres Moreno Carrascosa, Brian Stankus, Martina Cacciarini, , Theis I. Sølling
The Journal of Physical Chemistry Letters pp 9220-9225; https://doi.org/10.1021/acs.jpclett.1c02334

Abstract:
Excited-state chemistry lacks generalized symmetry rules. With many femtochemistry studies focused on individual cases, it is hard to build up the same level of chemical intuition for excited states as that for ground states. Here, we unravel the degrees of freedom involved in ultrafast internal conversion (IC) by mapping the vibrational coherence of the initial wavepacket and the dependence on molecular symmetry in various cyclic tertiary amines. Molecular symmetry plays an important role in the preservation of vibrational coherence in the transit from one electronic state to another. We show here that it is sufficient for the molecule to simply have the possibility of a more symmetric structure to achieve the preservation of vibrational coherence. It can be transient and still lead to preservation. This finding provides an additional angle on how symmetry influences electronic transitions and an additional piece to the puzzle of establishing symmetry-based selection rules for excited-state processes.
Jun Bo, Xiaojuan Sun, Peng Wan, Dong Huang, Xingtong Chen, Mengyu Chen, Rui Li, Dongyang Shen, Qinyi Li, Wenlin Xia, et al.
The Journal of Physical Chemistry Letters pp 9115-9123; https://doi.org/10.1021/acs.jpclett.1c02472

Abstract:
All-inorganic perovskite quantum dots (PQDs), potentially applicable to high-performance display technologies, are facing challenges when the superior luminescence properties with high stability and uncompromised electrical conductivity are combined. Here, by introducing hexylamine sulfate and reducing the reaction rate, we managed to optimize the surface sacrificial coating of CsPbBr3 QDs. As a result, the colloidal PQDs show a photoluminescence quantum efficiency (PLQE) of 95.8% in solution, and an internal PLQE as high as 97.8% in solid-state films. As far as stability is concerned, the PQDs not only show excellent resistance to polar solvent but also can retain over 84% of the initial PL intensity after continuous heating at 100 °C for 60 min. More importantly, the superior stability is achieved without compromising electrical conductivity. The light-emitting diodes made from these PQDs show a current efficiency of 8.9 cd A–1 with excellent thermal stability.
Xiang Huang, Li-Yong Gan, Jiong Wang, , Chang-Chun He,
The Journal of Physical Chemistry Letters pp 9197-9204; https://doi.org/10.1021/acs.jpclett.1c02665

Abstract:
Developing earth-abundant transition metal (TM)-based electrocatalysts toward oxygen reduction reaction (ORR) is significant in overcoming the high cost of fuel cells. Herein, using an as-synthesized proton-conductive coordination polymer (termed TM-DHBQ) as a template, we investigate the ORR performance of a series of such TM-DHBQs via screening 3d, 4d, and 5d TMs. We find that most 3d TM-DHBQs exhibit distinguished durability under ORR turnover conditions. The formation energies of these TM-DHBQs and adsorption free energies of ORR intermediates show a good correlation with the number of outer electrons of TM ions in TM-DHBQs, enabling the formation energy as a robust ORR activity descriptor. The Sabatier-type volcano plot and microkinetic modeling coidentify Fe- and Co-DHBQs as two promising alternatives to Pt-based ORR electrocatalysts. For those TM-DHBQs showing strong bonding to oxygen species, the ORR intermediate is found to combine with the TM ion serving as the active center.
The Journal of Physical Chemistry Letters pp 9169-9174; https://doi.org/10.1021/acs.jpclett.1c02721

Abstract:
Potential energy surfaces fit with basis set expansions have been shown to provide accurate representations of electronic energies and have enabled a variety of high-accuracy dynamics, kinetics, and spectroscopy applications. The number of terms in these expansions scales poorly with system size, a drawback that challenges their use for systems with more than ∼10 atoms. A solution is presented here using dictionary learning. Subsets of the full set of conventional basis functions are optimized using a newly developed multipass greedy regression method inspired by forward and backward selection methods from the statistics, signal processing, and machine learning literatures. The optimized representations have accuracies comparable to the full set but are 1 or more orders of magnitude smaller, and notably, the number of terms in the optimized multipass greedy expansions scales approximately linearly with the number of atoms.
Hongmin Zhang, Zhiqiang Zhang, Yameng Liu, Xiuzhong Fang, Junwei Xu, ,
The Journal of Physical Chemistry Letters pp 9188-9196; https://doi.org/10.1021/acs.jpclett.1c02471

Abstract:
Cation or anion vacancies in semiconducting oxides usually benefit activity for CO oxidation. To study the nature of vacancy engineering for a thermocatalytic reaction, we adopted lattice doping of cations with varied valence states to construct anion and cation vacancies in n-type and p-type semiconducting CeO2 and NiO, respectively. Doping cations can effectively regulate the number of the vacancies, thus tailoring the activity for CO oxidation. The strong correlation of activation energy and specific activity with a catalyst band gap verified that the nature of vacancy engineering for activity of CeO2 and NiO for CO oxidation can be attributed to tailoring of the band gap. The larger the vacancy amount, the smaller the band gap, and the lower the activation energy, thus giving a higher specific activity. Band-gap engineering, widely used for photocatalytic processes, can be a new tool for tailoring the activity of semiconducting oxide catalysts for thermocatalytic reactions.
The Journal of Physical Chemistry Letters pp 9108-9114; https://doi.org/10.1021/acs.jpclett.1c02574

Abstract:
Vibrational spectroscopy is key in probing the interplay between the structure and dynamics of aqueous systems. To map different regions of experimental spectra to the microscopic structure of a system, it is important to combine them with first-principles atomistic simulations that incorporate the quantum nature of nuclei. Here we show that the large cost of calculating the quantum vibrational spectra of aqueous systems can be dramatically reduced compared with standard path integral methods by using approximate quantum dynamics based on high-order path integrals. Together with state-of-the-art machine-learned electronic properties, our approach gives an excellent description not only of the infrared and Raman spectra of bulk water but also of the 2D correlation and the more challenging sum-frequency generation spectra of the water–air interface. This paves the way for understanding complex interfaces such as water encapsulated between or in contact with hydrophobic and hydrophilic materials through robust and inexpensive surface-sensitive and multidimensional spectra with first-principles accuracy.
Yuyan Liu, Yujin Ji,
The Journal of Physical Chemistry Letters pp 9149-9154; https://doi.org/10.1021/acs.jpclett.1c02487

Abstract:
The synthesis of 2D MoSi2N4 marked the birth of a new family of 2D MA2Z4 materials, whose potential applications are expected to sweep the field of nanoscale devices and catalysis in the future. In this work, we propose a multilevel screening workflow to systematically explore the mechanic stabilities, electronic properties, and hydrogen evolution performances of the 2D MA2Z4 family, among which seven stable, metallic, and highly active 2D MA2Z4 monolayers (2H-α-VGe2N4, 2H-α-NbGe2N4, 2H-α-TaGe2N4, 2H-α-NbSi2N4, 2H-β-VGe2N4, 2H-β-NbGe2N4, and 2H-β-TiGe2P4) are predicted as promising hydrogen evolution reaction (HER) catalysts with near-zero hydrogen adsorption free energy (ΔGH). The lowest unoccupied state energy (ELUS) of the MA2Z4 basal plane is identified as a concise descriptor to influence the electron filling and eventually determine its ΔGH. The criteria of −6.0 < ELUS < −5.6 eV is confirmed as the HER active window to explore novel HER catalysts. In particular, group-VI-terminated MA2Z4 basal planes have a higher ELUS (> −5.6 eV), which leads to weak H adsorption and poor HER activities accordingly.
Yuechen Gao,
The Journal of Physical Chemistry Letters pp 9124-9131; https://doi.org/10.1021/acs.jpclett.1c02486

Abstract:
The magic-angle twisted bilayer graphene (MATBG) recently attracted intensive research attention because of its fascinating and unconventional electronic properties. Herein, we claim the magic-angle phenomenon originates from the Heisenberg uncertainty principle, which can provide intensive explanations on finite size effect and twist-dependent low energy band variations. We showed that flat bands could exist only near the AA stacking structure rather than AB. The finite-size effect gives the minimal size of graphene quantum dots (R ≳ 4 nm) for the emergence of the Dirac point, and the uncertainty relation provides the upper bound for moiré supercells (R ≲ 23.5 nm) in twisted bilayer graphene, which is the quantum mechanical boundary for the emergence of flat bands. Combining the twist dependence of moiré supercell size, we proved that there is only one possible magic angle in MATBG at θ ≈ 1.1°. Our result implies that the unconventional phenomena in MATBG originate from the fundamental feature of condensed matter physics.
Meng Yu, , Tao Zeng, Chang Chen, Xiaojing Lin, Zhouxiang Ji, Fei Guo, Yuxiang Li, , Yuliang Dong
The Journal of Physical Chemistry Letters pp 9132-9141; https://doi.org/10.1021/acs.jpclett.1c02414

Abstract:
Different nucleotides generate specific ionic currents that discriminate between the nucleotides while they are passing through the nanopore constriction. MspA is a commonly used nanopore for DNA sequencing. However, the reasons of the current variation remain ambiguous. Our work unveils the microscopic mechanism of current variation for an ssDNA passing through the MspA nanopore by all-atom molecular dynamic simulations. Besides the physical rigidity and dimensions of the nucleotides, nucleotide orientation is observed to induce nonignorable current variation. Besides the generally considered MspA nanopore constriction, it is also found that the region below constriction could be used to detect and differentiate single nucleotides when the single-stranded DNA translocates in the form of base–constriction–base meshing and ratcheting across the nanopore constriction compared to other regions. The work provides a novel insight into facilitating the development of low-cost and high-throughput nanopore DNA sequencing.
The Journal of Physical Chemistry Letters pp 9162-9168; https://doi.org/10.1021/acs.jpclett.1c02609

Abstract:
The thermodynamic stability of water next to graphitic surfaces is of fundamental interest, as it underlies several natural phenomena and important industrial processes. It is commonly assumed that water wets graphite more than graphene due to increased, favorable van der Waals interactions between the interfacial water molecules with multiple carbon sheets. Here, we employed extensive computer simulations and analysis of the molecular correlation functions to show that the interfacial water thermodynamics is in fact dominated by surface entropy. We show that on graphite, destabilization of the interfacial hydrogen bond network leads to an overcompensating increase in population of low frequency translational and librational modes, which is ultimately responsible for the increased interfacial stability compared to graphene. The spectroscopic signature of this effect is an enhancement of the modes near 100 and 300 cm–1. This subtle interplay between entropy and surface binding may have important consideration for interpretations of various phenomena, including the hydrophobic effect.
Hui Wang, Jifeng Yuan, Jiahao Xi, Jiuyao Du,
The Journal of Physical Chemistry Letters pp 9142-9148; https://doi.org/10.1021/acs.jpclett.1c02682

Abstract:
The mismatched energy-level alignment and interface defects of the SnO2 nanoparticles’ electron transport layer (ETL) and perovskite layer worsen the efficiency of the perovskite solar cell. Herein, we devise a multiple-function surface engineering of SnO2 nanoparticles. TBA+ ions improve the dispersion and stability of colloidal T-SnO2 nanoparticles and act as a bridge between the ETL and perovskite layer through the electrostatic interaction with anions, thus suppressing the charge recombination and reducing the energy loss. I– ions passivate oxygen vacancies of SnO2 nanoparticles but also halide vacancies of the perovskite layer. Furthermore, the conduction band edge of T-SnO2 is enhanced to match the energy alignment with the perovskite, which reduces the energy offset for electron transfer. As a result, the champion solar cell based on T-SnO2 presented a power conversion efficiency of 21.71% with a VOC of 1.15 V and negligible hysteresis, which are much higher than those of the reference device.
Yang Zhou,
The Journal of Physical Chemistry Letters pp 9155-9161; https://doi.org/10.1021/acs.jpclett.1c02300

Abstract:
One of the most challenging aspects of semiconductor nanotechnology is the presence of extremely efficient nonradiative decay pathways (known as Auger processes) that hinder any attempt at creating population inversion and obtaining gain in nanocrystals. What is even more frustrating is that, in most cases, the strategies adopted to slow down Auger in these nanostructures also lead to a comparable increase in the radiative recombination times, so that there is no overall improvement from the point of view of their applicability as emissive media. Here we present a comprehensive theoretical characterization of CdTe tetrapods and show that in these versatile nanostructures it is possible to achieve a complete decoupling between radiative and Auger processes, where the latter can be strongly suppressed compared to spherical structures, by careful shape engineering, without affecting the efficiency of radiative recombination.
, Feifei Qiu, Ce Song, , Yi Luo
The Journal of Physical Chemistry Letters pp 9094-9099; https://doi.org/10.1021/acs.jpclett.1c02578

Abstract:
Controlling the photon emission property of a single molecule is an important goal for nano-optics. We propose here a new mechanism for a single-molecule optical switch that utilizes the in situ electric field (EF) in biased metallic nanojunctions to control photon emission of molecules with through-space charge transfer (TSCT) excited states. The EF-induced Stark effect is capable of flipping the order of the bright noncharge transfer state and dark TSCT state, resulting in the anticipated switching behavior. The proposed mechanism was theoretically verified by scanning tunneling microscope-induced electroluminescence from a naphtalenediimide cyclophane molecule under experimentally accessible conditions. Simulations show that the proposed switching effect can be obtained by changing either bias polarity, which alters the polarization of the field, or tip-height, which affects the magnitude of the field. Our finding indicates that the in situ EF could play an important role in the design of optoelectronic molecular devices.
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