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This study explores the optical properties of porous porphyrin cages through the use of spectroscopic techniques. The findings reveal that cages featuring electron-donating nitrogen functional groups display distinct alterations in their absorption spectra, including a red-shift and broadening of Soret bands, and a decrease in the Soret:Q-band ratio. The extent of conjugation within the cages significantly impacts their molar absorptivity, demonstrating a linear correlation with the number of saturated cage linkages and a superlinear increase for highly conjugated cages. The emission spectra of the cages largely mirror that of the monomer, barring fully conjugated cages. The relative fluorescence quantum yields differ among the cages, with some showing enhancements and others reductions, likely due to variations in cage rigidity. Time-resolved emission measurements indicate that the number of porphyrins in the cages affects the emission lifetime, with increased conjugation resulting in a shorter lifetime due to exciton delocalization. These insights underscore the potential of highly conjugated cages in optoelectronic devices, photosensitizers, and photocatalysts, given their effective light absorption and energy distribution capabilities.

The molecular engineering of fluorescent organic/polymeric materials, specifically those emitting in the deep red to near-infrared spectrum, is vital for advancements in optoelectronics and biomedicine. Perylene diimide (PDI), a well-known fluorescent scaffold, offers high thermal and photophysical stability but suffers from fluorescence quenching in solid or aggregate states due to intense π-πinteractions. To mitigate this, simple and versatile methods for strong PDI aggregate emission without extensive synthetic demands are highly desirable but still lacking. Here, we report a straightforward strategy to enhance the solid-state emission of PDI by introducing certain degree of through-space charge transfer (TSCT) viacontrolled radical polymerization, which can efficiently distort the typical face-to-face PDI stacking, enabling greatly enhanced deep red emission. This is achieved by growing electron-donating star-shape styrenic (co)polymers from a multidirectional electron-accepting PDI initiator. The incorporation of polycyclic aromatic monomers further shifted the emission into the near-infrared region, albeit with a reduced intensity. Overall, the emission of the PDI-based TSCT polymers can be systematically manipulated by leveraging the balance between PDI stacking and the TSCT degree, as confirmed by both experimental study and theoretical calculations. Our approach circumvents complex synthetic procedures, offering highly emissive materials with large Stokes shifts and showing broad potential for optoelectronic technology.

Two-dimensional (2D) layered metal dichalcogenides constitute a promising class of materials for photodetector applications due to their excellent optoelectronic properties. The most common photodetectors, which work on the principle of photoconductive or photovoltaic effects, however, require either the application of external voltage biases or built-in electric fields, which makes it challenging to simultaneously achieve high responsivities across broad-band wavelength excitation─especially beyond the material’s nominal band gap─while producing low dark currents. In this work, we report the discovery of an intricate phonon–photon–electron coupling─which we term the acoustophotoelectriceffect─in SnS2that facilitates efficient photodetection through the application of 100 MHz order propagating surface acoustic waves (SAWs). This effect not only reduces the band gap of SnS2but also provides the requisite momentum for indirect band gap transition of the photoexcited charge carriers, to enable broad-band photodetection beyond the visible light range, while maintaining pA-order dark currents─ without the need for any external voltage bias. More specifically, we show in the infrared excitation range that it is possible to achieve up to 8 orders of magnitude improvement in the material’s photoresponsivity compared to that previously reported for SnS2-based photodetectors, in addition to exhibiting superior performance compared to most other 2D materials reported to date for photodetection.

The role of charge transfer states in multi-exciton mechanisms has recently become a point of discussion due to the difficulty associated with modeling their contributions accurately. Intermolecular packing has been shown experimentally to heavily influence multi-exciton mechanisms, and therefore understanding how this affects the coupling is key to controlling these processes. Using a gas phase perylene dimer in a weakly coupled configuration as a case study, we employ two separate methods to model the coupling between the bright and correlated triplet 1TTstates as a function of relative displacement. For singlet fission, displaced geometries are found to yield large charge transfer contributions within a wavefunction overlap paradigm, unlike for aligned geometries. Triplet–triplet annihilation charge transfer couplings are conversely very weak due to a large energy gap. We found that slipping of the dimer cofacial geometry is beneficial to both charge transfer-mediated processes within a wavefunction overlap scheme. However, within a fragment excitation difference (FED) scheme, a 1 Å slip is more beneficial than a 2 Å one. The resulting rates for singlet fission are in the femtosecond range, up to 22 ps–1, while for triplet fusion they are in the nanosecond range, up to 707 μs–1. By studying the dynamics of the triplet pair following singlet fission, we show that the decorrelation time scale depends on the nature of the relative molecular motion, ranging from picoseconds for fluctuations in the monomer orientations to microseconds for coplanar fluctuations. The direct comparison of the wavefunction overlap and FED methods yields an expected differential due to the method of calculation (linear-response vs multireference) but still strong agreement, suggesting that the more exact wavefunction overlap method can be substituted for the FED method in larger systems with minimal loss in accuracy vs computational complexity. These results provide a good stepping stone for further investigations into singlet fission related problems, correlating well with experiments despite the weakly coupled nature of the dimer.

• Newly designed janus semiconductor is a potential photocatalyst for overall water-splitting. • Clean fuel generation of hydrogen and oxygen through solar energy. • Very optimum electronic bandgap of 1.88 eV for water splitting. • Wide range of electronic and optical bandgap tuning possible by applying compressive strain. • Compressive strain application in a lattice direction improves not only solar light harvesting wavelength range but also the intensity. Photoelectrochemical water splitting using solar energy, generating oxygen and hydrogen is one of the clean fuel production processes. Inspired by surface-dependent characteristics of Janus structures, a newly designed Janus monolayer Silicon Phosphorous Arsenide (SiPAs) was analyzed with Density Functional Theory (DFT) methods. Hybrid exchange-correlation functional (HSE06) combined with Wannier90-based analysis for electronic and optical properties of SiPAs reveals that it can act as a photocatalyst. SiPAs show an indirect bandgap of 1.88 eV, absorbing visible light range is 350 to 500 nm. The phonon spectrum confirms dynamic stability. The exciton binding energy is computed with GW/BSE methods. The electronic band edge positions are at -5.75 and -4.43 eV, perfectly straddling the water redox potentials. Interestingly the strain application modifies the bandgap and also non-homogenously widens the absorption band. A novel range of photocatalyst designs with Group IV-V elements with great promise for water-splitting, photovoltaic, and narrow bandgap semiconductor (optoelectronics) applications may be feasible. [Display omitted] [ABSTRACT FROM AUTHOR]

The size-dependent pressure response of oleate-stabilized CdSe quantum dots (QDs) in paraffin is investigated using diamond anvil cell experiments and density functional theory (DFT). For QDs above 3.0 nm, the photoluminescence shows a blue-shift of around 43 meV/GPa, close to the value for bulk CdSe, but the shift increases strongly for nanocrystals less than 3 nm in size. Conversely, the absorption shift is 45 meV/GPa above 3.0 nm but weakens to 35 meV/GPa for particles 1.5 nm in size. No crystallographic phase transitions occur below 2 GPa, and the optical effects are reversible. DFT calculations confirm that shifts in the bulk modulus begin for sizes estimated to be 1/2 of the Bohr radius, which we term the extreme confinement regime.

The use of liquid gallium as a solvent for catalytic reactions has enabled access to well-dispersed metal atoms configurations, leading to unique catalytic phenomena, including activation of neighbouring liquid atoms and mobility-induced activity enhancement. To gain mechanistic insights into liquid metal catalysts, here we introduce a GaSn0.029Ni0.023liquid alloy for selective propylene synthesis from decane. Owing to their mobility, dispersed atoms in a Ga matrix generate configurations where interfacial Sn and Ni atoms allow for critical alignments of reactants and intermediates. Computational modelling, corroborated by experimental analyses, suggests a particular reaction mechanism by which Sn protrudes from the interface and an adjacent Ni, below the interfacial layer, aligns precisely with a decane molecule, facilitating propylene production. We then apply this reaction pathway to canola oil, attaining a propylene selectivity of ~94.5%. Our results offer a mechanistic interpretation of liquid metal catalysts with an eye to potential practical applications of this technology.

Benefiting from their ordered orientation and superior stability compared to traditional conjugated materials, hydrogen bonding (HB)-induced H-aggregates in organic small molecule hole-transport materials (HTMs) hold a big potential for high-performance inverted perovskite solar cells (IPSCs). However, H-aggregates can also lead to excessive face-aggregation by forming the gaps between aggregates, which is in turn unfavorable for charge mobility and thus for the overall device performance. Herein, we design and synthesize a new set of HB-containing triphenylamine-based small molecules to tailor the degree of H-aggregation, namely O1 (without HB), O2 (unilateral HB unit), and O3 (bilateral HB units). These HTMs make a clear trade-off effect on the charge mobility within the HTM and the interfacial properties of perovskite and HTM. Although the interfacial hole extraction process is promoted upon the HB-functionalized interface, the best performance of IPSCs is still achieved by O1 HTM, which is mainly influenced by the higher hole mobility without HB-induced H-aggregates. Nevertheless, the photo stability of as-fabricated devices is effectively improved upon the HB passivation effect on the interface of HTM (O2 or O3) and perovskite, as well as the better quality of atop perovskite layers with less grain boundary compared to the reference case (O1).

Indium nitride (InN) has been of significant interest for creating and studying two-dimensional electron gases (2DEG). Herein we demonstrate the formation of 2DEGs in ultrathin doped and undoped 2D InN nanosheets featuring high carrier mobilities at room temperature. The synthesis is carried out via a two-step liquid metal-based printing method followed by a microwave plasma-enhanced nitridation reaction. Ultrathin InN nanosheets with a thickness of ∼2 ± 0.2 nm were isolated over large areas with lateral dimensions exceeding centimeter scale. Room temperature Hall effect measurements reveal carrier mobilities of ∼216 and ∼148 cm2V–1s–1for undoped and doped InN, respectively. Further analysis suggests the presence of defined quantized states in these ultrathin nitride nanosheets that can be attributed to a 2D electron gas forming due to strong out-of-plane confinement. Overall, the combination of electronic and plasmonic features in undoped and doped ultrathin 2D InN holds promise for creating advanced optoelectronic devices and functional 2D heterostructures.

Ab initio treatments of interexcited state internal conversion (IC) are more often than not missing from exciton dynamic descriptions, because of their inherent complexity. Here, we define ”interexcited state IC” as a same-spin nonradiative transition between states iand j, where i≠ j≠ 0. Competing directly with multiexciton processes such as singlet fission or triplet photoupconversion, inclusion of this mechanism in the narrative of molecular photophysics would allow for strategic synthesis of chromophores for more efficient photon-harvesting applications. Herein, we present a robust formalism which can model these rates using density functional theory (DFT)-based methods within the Franck–Condon and Herzberg–Teller regime. Using an unsubstituted diketo-pyrrolopyrrole (DPP) core as a case study, we illustrate the exciton dynamics along the first four excited states for both singlet and triplet manifolds, showing ultrafast same-spin transfer mechanisms due to all excited states, excluding the first triplet level, being in close energetic proximity (within 0.8 eV of each other). The resulting electron same-spin rates outcompete the electron spin-flipping intersystem crossing (ISC) rates, with excitons firmly obeying Kasha’s rule as they cascade down from the high-lying excited states toward the lower states. Furthermore, we calculated that only the first singlet excited state displayed a reasonable probability of triplet exciton generation, of ∼40%, with a near-zero chance of the exciton reverting to the singlet manifold once the electron–hole pair are of parallel spin.

Lead-based halide perovskite nanocrystals (NCs) are recognized as emerging emissive materials with superior photoluminescence (PL) properties. However, the toxicity of lead and the swift chemical decomposition under atmospheric moisture severely hinder their commercialization process. Herein, we report the first colloidal synthesis of lead-free Cs4CuIn2Cl12layered double perovskite NCs via a facile moisture-assisted hot-injection method stemming from relatively nontoxic precursors. Although moisture is typically detrimental to NC synthesis, we demonstrate that the presence of water molecules in Cs4CuIn2Cl12synthesis enhances the PL quantum yield (mainly in the near-UV range), induces a morphological transformation from 3D nanocubes to 2D nanoplatelets, and converts the dark transitions to radiative transitions for the observed self-trapped exciton relaxation. This work paves the way for further studies on the moisture-assisted synthesis of novel lead-free halide perovskite NCs for a wide range of applications.

Insights into metal–matrix interactions in atomically dispersed catalytic systems are necessary to exploit the true catalytic activity of isolated metal atoms. Distinct from catalytic atoms spatially separated but immobile in a solid matrix, here we demonstrate that a trace amount of platinum naturally dissolved in liquid gallium can drive a range of catalytic reactions with enhanced kinetics at low temperature (318 to 343 K). Molecular simulations provide evidence that the platinum atoms remain in a liquid state in the gallium matrix without atomic segregation and activate the surrounding gallium atoms for catalysis. When used for electrochemical methanol oxidation, the surface platinum atoms in the gallium–platinum system exhibit an activity of ~2.8×107mAmgPt−1,three orders of magnitude higher than existing solid platinum catalysts. Such a liquid catalyst system, with a dynamic interface, sets a foundation for future exploration of high-throughput catalysis.

It is well-understood that during the liquid-to-solid phase transition of alloys, elements segregate in the bulk phase with the formation of microstructures. In contrast, we show here that in a Bi–Ga alloy system, highly ordered nanopatterns emerge preferentially at the alloy surfaces during solidification. We observed a variety of transition, hybrid and crystal-defect-like patterns, in addition to lamellar and rod-like structures. Combining experiments and molecular dynamics simulations, we investigated the influence of the superficial Bi and Ga2O3layers during surface solidification and elucidated the pattern-formation mechanisms, which involve surface-catalysed heterogeneous nucleation. We further demonstrated the dynamic nature and robustness of the phenomenon under different solidification conditions and for various alloy systems. The surface patterns we observed enable high-spatial-resolution nanoscale-infrared and surface-enhanced Raman mapping, which reveal promising potential for surface- and nanoscale-based applications.

We investigate dispersion interactions in a selection of atomic, molecular, and molecule–surface systems, comparing high-level correlated methods with empirically corrected density functional theory (DFT). We assess the efficacy of functionals commonly used for surface-based calculations, with and without the D3 correction of Grimme. We find that the inclusion of the correction is essential to get meaningful results, but there is otherwise little to distinguish between the functionals. We also present coupled-cluster quality interaction curves for H2, NO2, H2O, and Ar interacting with large carbon flakes, acting as models for graphene surfaces, using novel absolutely localized molecular orbital based methods. These calculations demonstrate that the problems with empirically corrected DFT when investigating dispersion appear to compound as the system size increases, with important implications for future computational studies of molecule–surface interactions.

We introduce a nonclassical model for nanocrystal nucleation in solution which centers on the dynamic interplay of chemical bond breakage and formation coupled with the desolvation of precursor molecules, which we term the molecular chemistry (MC) model. Departing from classical theory, our model employs the bond count as the key variable rather than particle size, thereby redefining the role of supersaturation and its role in determining the so-called critical nucleus size. We apply the model to CdSe nanocrystal formation in nonpolar solvents and showcase its efficacy in predicting solvent dynamics, precursor characteristics, crystal phase, stoichiometry, “magic number” behavior, and transition states. While the coupled-cluster method is used to determine the bond energy, we show that it is possible to derive reaction pathways by reducing the calculations to algebraic approximations for the nucleation energy. This singular set of bond energy parameters allows nanocrystal nucleation and growth to be conceptualized as a straightforward chemical reaction.

Excitons in organic crystalline semiconductors play a crucial role in the operation of optoelectronic devices, such as organic solar cells, light-emitting diodes, and photodetectors. The excitonic properties of materials are dramatically affected by the presence of surfaces and interfaces. Using the GW method and Bethe–Salpeter equation, we investigate the influence of a neutral hydrogen-passivated 1 × 2 reconstructed (100) silicon substrate on excitons within the crystalline tetracene layer deposited on the top of it. Our findings reveal that singlet excitons in the contact tetracene layer are situated within the continuum of unbound Wannier-Mott excitonic states in silicon, with noteworthy hybridization between these states. Consequently, in the contact tetracene layer, all singlet excitons exhibit a pronounced interlayer charge transfer character, while the triplet exciton remains confined to the tetracene layer. This makes the singlet fission effect highly improbable for the contact tetracene layer. Additionally, the presence of the silicon substrate results in a modification of the singlet–triplet gap by 144 meV. This change is solely attributed to hybridization with excitons in silicon, which influences the exchange energy. Our results show that the dynamic dielectric screening caused by the substrate does not impact the singlet–triplet gap but alters the exciton binding energies.

Two-dimensional (2D) organic–inorganic metal halide perovskites have gained immense attention as alternatives to three-dimensional (3D) perovskites in recent years. The hydrophobic spacers in the layered structure of 2D perovskites make them more moisture-resistant than 3D perovskites. Moreover, they exhibit unique anisotropic electrical transport properties due to a structural confinement effect. In this study, four lead-free Dion–Jacobson (DJ) Sn-based phase perovskite single crystals, 3AMPSnI4, 4AMPSnI4, 3AMPYSnI4, and 4AMPYSnI4[AMP = (aminomethyl)-piperidinium, AMPY = (aminomethyl)pyridinium] are reported. Results reveal structural differences between them impacting the resulting optical properties. Namely, higher octahedron distortion results in a higher absorption edge. Density functional theory (DFT) is also performed to determine the trends in energy band diagrams, exciton binding energies, and formation energies due to structural differences among the four single crystals. Finally, a field-effect transistor (FET) based on 4AMPSnI4is demonstrated with a respectable hole mobility of 0.57 cm2V–1s–1requiring a low threshold voltage of only −2.5 V at a drain voltage of −40 V. To the best of our knowledge, this is the third DJ-phase perovskite FET reported to date.

Two-dimensional (2D) metal organic framework (MOF) or metalloporphyrin nanosheets with a stable metal-N4complex unit present the metal as a single-atom catalyst dispersed in the 2D porphyrin framework. First-principles calculations on the 3d-transition metals in M-TCPP are investigated in this study for their surface-dependent electronic properties including work function and d-band center. Crystal orbital Hamiltonian population (-pCOHP) analysis highlights a higher contribution of the bonding state in the M–N bond and antibonding state in the N–N bond to be essential for N–N bond activation. A linear relationship between ΔGmaxand surface electronic properties, N–N bond strength, and Bader charge has been found to influence the rate-determining potential for nitrogen reduction reaction (NRR) in M-TCPP MOFs. 2D Ti-TCPP MOF, with a kinetic energy barrier of 1.43 eV in the final protonation step of enzymatic NRR, shows exclusive NRR selectivity over competing hydrogen reduction (HER) and nitrogenous compounds (NO and NO2). Thus, Ti-TCPP MOF with an NRR limiting potential of −0.35 V in water solvent is proposed as an attractive candidate for electrocatalytic NRR.

In this article, we present multiscale modeling of triplet exciton energy migrating through the archetypical poly(p-phenylene vinylene) (PPV) polymer in the crystal phase. We combine electronic structure calculations with coupled exciton-nuclear quantum dynamics in order to parameterize exciton evolution in J- and H-aggregate configurations. We then apply this parameterization to a master-equation approach to describe transport at the nanoscale. We find that triplet transport is characterized by two remarkably different components: a fast and coherent intrachain and a slow and incoherent interchain. Energy migration along the polymer backbone is accompanied by coherent superpositions developing between neighboring sites in the first 20 fs; however, no interchain coherence develops. The nonequilibrium exciton density exhibits an initial ultrafast ballistic spread followed by normal diffusive propagation. At room temperature, the diffusion coefficients along the respective interchain axes are found to be Da= 2.48 × 10–2cm2s–1, Db= 4.18 × 10–2cm2s–1, and Dc= 3.03 cm2s–1along the fast axis.

We report the synthesis of centimeter sized ultrathin GaN and InN. The synthesis relies on the ammonolysis of liquid metal derived two-dimensional (2D) oxide sheets that were squeeze-transferred onto desired substrates. Wurtzite GaN nanosheets featured typical thicknesses of 1.3 nm, an optical bandgap of 3.5 eV and a carrier mobility of 21.5 cm2V–1s–1, while the InN featured a thickness of 2.0 nm. The deposited nanosheets were highly crystalline, grew along the (001) direction and featured a thickness of only three unit cells. The method provides a scalable approach for the integration of 2D morphologies of industrially important semiconductors into emerging electronics and optical devices.

Liquid phase exfoliation techniques of layered crystals establish the basis for high yield production of two-dimensional (2D) flakes suspension. However, such techniques generally require a long processing time. The recent demonstration of the piezoelectric phenomenon in noncentrosymmetric layered transition metal dichalcogenides, such as molybdenum disulfide (MoS2), leads to new opportunities for fast and efficient exfoliation processes. Here we use concomitant electric field and mechanical shear force for producing a suspension of MoS2nanoflakes from exfoliation of their layered bulk powder particles. The electrical and mechanical fields are applied by a surface acoustic wave (SAW) microcentrifugation device. We show that the overall yield per unit of time of 3.816%/h can be achieved, which is at least an order of magnitude larger than previously reported liquid phase exfoliation methods. Simultaneously, the impressive monolayer yield is 58% in an excellent agreement with the computational estimation based on electric field assisted density functional theory calculations. The work therefore reports two major advancements. We show efficient exfoliation of layered MoS2. More importantly, we demonstrate the importance of the electric field in increasing the efficiency of liquid phase exfoliation. It is thus expected that these outcomes to fundamentally impact research activities focused on the exfoliation of piezoelectric 2D materials.

Atomically thin semiconductors are one of the fastest growing categories in materials science due to their promise to enable high-performance electronic and optical devices. Furthermore, a host of intriguing phenomena have been reported to occur when a semiconductor is confined within two dimensions. However, the synthesis of large area atomically thin materials remains as a significant technological challenge. Here we report a method that allows harvesting monolayer of semiconducting stannous oxide nanosheets (SnO) from the interfacial oxide layer of liquid tin. The method takes advantage of van der Waals forces occurring between the interfacial oxide layer and a suitable substrate that is brought into contact with the molten metal. Due to the liquid state of the metallic precursor, the surface oxide sheet can be delaminated with ease and on a large scale. The SnO monolayer is determined to feature p-type semiconducting behavior with a bandgap of ∼4.2 eV. Field effect transistors based on monolayer SnO are demonstrated. The synthetic technique is facile, scalable and holds promise for creating atomically thin semiconductors at wafer scale.

Insertion of interfacial molecules in bulk heterojunction and dye sensitized solar cells is effective to retard charge recombination reactions and thus to improve solar cell performance. So far, to extend charge separated state lifetime, the molecule was designed to increase distance between an n-type and a p-type semiconductors to reduce their electronic coupling. Here we investigated a series of thiophene–fluorene molecular wires on the TiO2nanoporous surface and propose a model to explain a long-lived charge separated state. The polymer wire acts as a sensitizer aligned in parallel to the TiO2surface and injects an electron into the TiO2with electron injection efficiency of >80%. Time-resolved microwave conductivity measurements suggest that a generated hole can be mobile, and we found with DFT calculation that a hole appears to be localized at the thiophene units which are not directly attached to the TiO2surface. Charge recombination between the mobile electron in the TiO2and the hole at the thiophene units is retarded to >100 ms compared to the reaction at the monomer/TiO2interface with ∼5 ms. Monte Carlo simulation supports that this slow charge recombination occurs with the localization of the hole at the thiophene units.

A non-empirical equation describing the effect of size on the temperature dependence of the optical bandgap of CdS (dEg/dT) is obtained on the basis of the Brus equation. Intriguingly, we find that dEg/dTdiverges strongly from bulk values only within the “extreme confinement” (EC) regime. We conducted both experimental and theoretical investigations of the absorption spectra of CdS clusters and quantum dots as a function of temperature above room temperature. Our results show that the value of dEg/dTobtained from absorption spectra in the EC regime is 2.5 times higher than in the strong confinement regime. Notable ligand sensitivities are also observed for dEg/dTin the case of CdS clusters. Ab initiomolecular dynamics simulations and density functional theory calculations reveal that thermal fluctuations are the crucial factor influencing the bandgap temperature coefficient. Our results help resolve some long-standing debates regarding the dEg/dTbehavior of semiconductor quantum dots.

Halide perovskites have attracted enormous attention due to their potential applications in optoelectronics and photocatalysis. However, concerns over their instability, toxicity, and unsatisfactory efficiency have necessitated the development of lead-free all-inorganic halide perovskites. A major challenge in designing efficient halide perovskites for practical applications is the lack of effective methods for producing nanocrystals with precise size and shape control. In this work, a layered perovskite, Cs4ZnSb2Cl12(CZS), is found from calculations to exhibit size- and facet-dependent optoelectronic properties in the nanoscale, and thus, a colloidal method is used to synthesize the CZS nanoparticles with size-tunable morphologies: zero- (nanodots), one- (nanowires and nanorods), two- (nanoplates), and three-dimensional (nanopolyhedra). The growth kinetics of the CZS nanostructures, along with the effects of surface ligands, reaction temperature, and time were investigated. The optoelectronic properties of the nanocrystals varied with size due to quantum confinement effects and with shape due to anisotropy within the crystals and the exposure of specific facets. These properties could be modulated to enhance the visible-light photocatalytic performance for toluene oxidation. In particular, the 9.7 nm CZS nanoplates displayed a toluene to benzaldehyde conversion rate of 1893 μmol g–1h–1(95% selectivity), 500 times higher than the bulk synthesized CZS, and comparable with the reported photocatalysts. This study demonstrates the integration of theoretical calculations and synthesis, revealing an approach to the design and fabrication of novel, high-performance colloidal perovskite nanocrystals for optoelectronic and photocatalytic applications.

Nitrogen dioxide (NO2) is a gas species that plays an important role in certain industrial, farming, and healthcare sectors. However, there are still significant challenges for NO2sensing at low detection limits, especially in the presence of other interfering gases. The NO2selectivity of current gas-sensing technologies is significantly traded-off with their sensitivity and reversibility as well as fabrication and operating costs. In this work, we present an important progress for selective and reversible NO2sensing by demonstrating an economical sensing platform based on the charge transfer between physisorbed NO2gas molecules and two-dimensional (2D) tin disulfide (SnS2) flakes at low operating temperatures. The device shows high sensitivity and superior selectivity to NO2at operating temperatures of less than 160 °C, which are well below those of chemisorptive and ion conductive NO2sensors with much poorer selectivity. At the same time, excellent reversibility of the sensor is demonstrated, which has rarely been observed in other 2D material counterparts. Such impressive features originate from the planar morphology of 2D SnS2as well as unique physical affinity and favorable electronic band positions of this material that facilitate the NO2physisorption and charge transfer at parts per billion levels. The 2D SnS2-based sensor provides a real solution for low-cost and selective NO2gas sensing.

The prediction of the photoluminescence line-shape of defect systems from first principles is becoming an important tool for the discovery of quantum emission defects in semiconductors. Using a sequence of density functional theory calculations based on the VASP code, PyPhotonics calculates the Huang-Rhys factor and plots the photoluminescence line-shape of the defect by processing the VASP output. Program title: PyPhotonics CPC Library link to program files: https://doi.org/10.17632/vy4ccz4hxz.1 Developer's repository link: https://github.com/sheriftawfikabbas/pyphotonics Licensing provisions: GNU General Public License 3 Programming language: Python 3.9 Nature of problem: While density functional theory (DFT) codes can calculate properties of crystal defects, there are no available codes to calculate the photoluminescence line-shape and the Huang-Rhys factors for the defects computed using DFT. Solution method: The PyPhotonics python code is a post-processing library written entirely in python, which takes as input the output files of the VASP and phonopy codes for a defect system, and calculates the Huang-Rhys factor and the PL lineshapes for that system. [ABSTRACT FROM AUTHOR]

Chemical reaction studies of N-methyl-N-propyl-pyrrolidinium-bis(fluorosulfonyl)imide-based ionic liquid with the lithium metal surface were performed using ab initio molecular dynamics (aMD) simulations and X-ray Photoelectron Spectroscopy (XPS). The molecular dynamics simulations showed rapid and spontaneous decomposition of the ionic liquid anion, with subsequent formation of long-lived species such as lithium fluoride. The simulations also revealed the cation to retain its structure by generally moving away from the lithium surface. The XPS experiments showed evidence of decomposition of the anion, consistent with the aMD simulations and also of cation decomposition and it is envisaged that this is due to the longer time scale for the XPS experiment compared to the time scale of the aMD simulation. Overall experimental results confirm the majority of species suggested by the simulation. The rapid chemical decomposition of the ionic liquid was shown to form a solid electrolyte interphase composed of the breakdown products of the ionic liquid components in the absence of an applied voltage.

The accuracy of total electronic energies obtained using the fixed-node diffusion quantum Monte Carlo (FN-DMC) method is determined by the choice of the many-body nodal surface. Here, we perform a systematic comparison of the quality of FN-DMC energies for a selection of atoms and diatomic molecules using nodal surfaces defined by single determinants of Hartree–Fock, B3LYP, and LDA orbitals. Through comparison with experimental results, we show that the use of Kohn–Sham orbitals results in significantly improved FN-DMC atomization energies over those obtained using Hartree–Fock orbitals. We also discuss the effect of spin contamination in the orbitals.

We use computer simulation to explore phenomena which could be used to grow arbitrary arrangements of nanostructures on metal surfaces via the vacuum deposition process. The method involves a three-stage process where, in the first “pattern formation stage”, a desired pattern of adatom islands is created on a base metal substrate, followed by a second “fixing stage” where an immiscible metallic species is vacuum deposited on the substrate at elevated temperatures to fill vacancy islands, and a final “growth stage” involving the further vacuum deposition of specific metal or nonmetal atomic species. In this work, we use molecular dynamic (MD) simulations to study the self-ordering behavior in the “fixing” and “growth” stage of assembly. We use the model immiscible systems Pt/Ag and Pt/Au with Pt as the base substrate. It was observed in the “fixing” stage that immiscible species deposited at higher temperatures would readily move off substrate adatom islands effectively “flooding” the vacancy areas around the islands, eventually forming a structurally stable, atomically smooth surface of alternating atomic species. In the “growth” stage, substrate species deposited at lower temperatures on such patterned surfaces were observed to preferentially move off surface regions covered by the immiscible species and onto the original adatom island areas, sometimes aggregating into nanostructures several atomic layers high.

We present the first benchmarking study of nonadiabatic matrix coupling elements (NACMEs) calculated using different density functionals. Using the S1→ S0transition in perylene solvated in toluene as a case study, we calculate the photophysical properties and corresponding rate constants for a variety of density functionals from each rung of Jacob’s ladder. The singlet photoluminescence quantum yield (sPLQY) is taken as a measure of accuracy, measured experimentally here as 0.955. Important quantum chemical parameters such as geometries, absorption, emission, and adiabatic energies, NACMEs, Hessians, and transition dipole moments were calculated for each density functional basis set combination (data set) using density functional theory based multireference configuration interaction (DFT/MRCI) and compared to experiment where possible. We were able to derive simple relations between the TDDFT and DFT/MRCI photophysical properties; with semiempirical damping factors of ∼0.843 ± 0.017 and ∼0.954 ± 0.064 for TDDFT transition dipole moments and energies to DFT/MRCI level approximations, respectively. NACMEs were dominated by out-of-plane derivative components belonging to the center-most ring atoms with weaker contributions from perturbations along the transverse and longitudinal axes. Calculated theoretical spectra compared well to both experiment and literature, with fluorescence lifetimes between 7.1 and 12.5 ns, agreeing within a factor of 2 with experiment. Internal conversion (IC) rates were then calculated and were found to vary wildly between 106–1016s–1compared with an experimental rate of the order 107s–1. Following further testing by mixing data sets, we found a strong dependence on the method used to obtain the Hessian. The 5 characterized data sets ranked in order of most promising are PBE0/def2-TZVP, ωB97XD/def2-TZVP, HCTH407/TZVP, PBE/TZVP, and PBE/def2-TZVP.

The reconstructed geometries, surface energies, surfactant adsorption energies, and work function have been calculated for the nonpolar (101̅0) and (112̅0) surfaces of wurtzite CdSe. This study was undertaken in the framework of ab initio density functional theory. Passivation with an amine or phosphine group lowers the surface energy of both nonpolar surfaces. However, thiol passivation of (101̅0) increases its surface energy. Both (101̅0) and (112̅0) tend to maintain their bulklike structure more so when passivated. The surface work function of (101̅0) and (112̅0) decreased with amine and phosphine passivation; amine had a more marked effect. Thiol passivation, on the other hand, increased the work function of both surfaces studied.

The stability of nitrogen incorporation at protonated titanium vacancy sites, V Ti+ nH, n= 0−4, and interstitial sites in anatase under oxygen-rich growth conditions has been investigated using density functional theory quantum mechanical modeling. The 0 K DFT energy results were corrected using thermodynamic free energy data to obtain defect formation energies, Ed, at a typical sol−gel calcination temperature of 700 K. Doping of sol−gel anatase was simulated using a 2 × 2 × 1 defected anatase supercell as host, in which one Ti atom was replaced by 4 H atoms, giving [H 4]Ti 15O 32. A number of different nitrogen configurations were found to be stable at V Tisites in the defected anatase, having negative or small positive Edvalues at 700 K. These included nitrogen bonded to one, two and three framework oxygen atoms and NH bonded to two framework oxygens, HNO 2. Maximum stability due to codoping with H was obtained with one H atom per V Ti, although models with up to 3 codoped H atoms gave negative Edvalues. An interesting observation was that extra stability was obtained in models where the structure relaxed to give bonding between the N at the V Tisite and one of the surrounding Ti atoms, with a Ti−N distance of ∼2 Å. Electronic structure calculations showed that the 2p orbitals of N at a V Tisite mix with both O 2p states at the top of the valence band and with Ti 3d states at the bottom of the conduction band. A small amount (∼0.1 eV) of band gap narrowing occurs for N doping at V Ti.

The stability of boron and carbon dopants (D) at vacant octahedral sites in rutile has been investigated using density functional theory quantum mechanical (QM) modeling. Three different types of sites were considered:  vacant Ti lattice site (Dvac), vacant Ti site Ti interstitial (DFrenkel), and interstitial site (Dint). The defect formation energies, Ed, at different temperatures and gas partial pressures were calculated from the QM total energies of the relaxed defect and host structures, combined with chemical potentials of the reservoir components that were corrected for both temperature and gas partial pressure variations. The contribution of vibrational free energy to Edas a function of temperature was evaluated for the BFrenkelmodel using ab initio phonon density of states calculations. The calculated vibrational and configurational free energy terms were of opposite sign and partially cancelled, giving a relatively small (0.3 eV at 700 K) combined contribution to Ed. Under strongly reducing conditions at 1500 K, boron incorporation at interstitial and Frenkel sites is favored, with Edvalues of 0.53 and 0.8 eV respectively, whereas the Edvalues for carbon doping were high (>4 eV) for all three models under high-temperature reducing conditions. Under oxygen-rich conditions relevant to sol−gel processing, the Dvacmodel was favored for both boron and carbon. Further stabilization of the Dvacmodel for boron was obtained at a protonated vacancy site, giving Ed1.16 eV for (BH)vacat 700 K.