The Journal of Physical Chemistry Letters最新文献

Both absorption and emission of light in semiconductor quantum dots occur through excitation or recombination of confined electron-hole pairs, or excitons, with tunable size-dependent resonant frequencies that are ideal for applications in various fields. Some of these applications require control over quantum dot shape uniformity, while for others, control over energy splittings among exciton states emitting light in different polarizations and/or between bright and dark exciton states is of key importance. These splittings, known as exciton fine structure, are very sensitive to the nanocrystal shape. Theoretically, nanocrystals of spheroidal shape are often considered, and their nonsphericity is treated perturbatively as stemming from a linear uniaxial deformation of a sphere. Here, we compare this treatment with a nonperturbative model of a cylindrical box, free of any restrictions on the cylinder's aspect ratio. This comparison allows one to understand the limits of validity of the traditional perturbative model and offers insights into the relative importance of various mechanisms controlling the exciton fine structure. These insights are relevant to both colloidal nanocrystals and epitaxial quantum dots of III-V and II-VI semiconductors.

Nanopore sensing is now reshaping analytical proteomics with its simplicity, convenience, and high sensitivity. Determining the length of polyglutamine (polyQ) is crucial for the rapid screening of Huntington's disease. In this computational study, we present a cross-nanoslit detection approach to determine the polyQ length, where the nanoslit is carved within a two-dimensional (2D) in-plane heterostructure of graphene (GRA) and hexagonal boron nitride (hBN). We designed a heterostructure with an hBN strip embedded in the graphene sheet. With such a design, polyQ peptides can spontaneously and linearly stretch out on the hBN stripe. By tuning the strength of an external in-plane electric field, molecular transportation of polyQ peptides along the hBN stripe can be effectively regulated. Subsequent cross-nanoslit motion can be applied to record time-dependent electric signals. The signal features are then utilized to train the machine learning classification models. The machine-learning-assisted recognition enables accurate determination of the protein's length. This nanoslit-sensing method may offer theoretical guidance on 2D heterostructure design for the detection of polyQ peptide lengths and rapid screening of protein-related diseases.

Self-powered broadband photodetection has evoked increased interest in next-generation photoelectronic devices. However, realizing self-powered broadband photodetection in a single material is still a challenge because of the harsh requirements, including powerful built-in field, excellent charge transport behaviors, as well as the broad absorption. Herein, we first realize broadband photodetection in the range from X-ray to UV-vis light in a polar two-dimensional perovskite (2-FBA)₂MAPb₂I₇ (2-FBA = 2-fluorobenzylamine, MA = methylamine) by incorporating an aromatic spacer into a three-dimensional prototype. As a result, (2-FBA)₂MAPb₂I₇ exhibited a superior response to UV-vis light (377 to 637 nm) without voltage bias. Specifically, a high switching ratio of 1.05 × 10⁴, an outstanding responsivity (R) of 1420 mA W^-1, and detectivity (D*) of 1.59 × 10¹³ Jones were achieved under light illumination at 520 nm. Moreover, (2-FBA)₂MAPb₂I₇ achieved a high sensitivity of 46.4 μC Gy^-1 cm^-2 without voltage bias, two times higher than that of a commercial α-Se film detector (20 μC Gy^-1 cm^-2). The sensitivity can be further improved to 3316 μC Gy^-1 cm^-2 at a 50 V bias. These results give insight into the design of 2D perovskites for self-powered broadband photodetection.

Reverse intersystem crossing (RISC) has become possible by minimizing the energy gap between the first excited singlet (S₁) and triplet state (T₁), which facilitates the thermally activated delayed fluorescence (TADF). Due to the small singlet-triplet energy gap, the S₁ and T₁ states exhibit comparable redox reactivity, leading organic TADF compounds to be potent photocatalysts. Here, we report such TADF compounds with multiple donor units designed as an efficient photocatalyst for the direct C(sp³)-H carbamoylation of saturated aza-heterocycles. The results obtained by photophysical investigations and chemical calculations confirm that both the S₁ and T₁ states are involved in the photocatalysis cycle, with the fast spin-flip from the S₁ to triplet states being a crucial factor in the enhancement of catalytic performance. The findings will be beneficial for the design of novel, efficient organic photocatalysis with TADF characteristics and aid in the development of organic photocatalysis.

The effects of methyl substitution on the ultrafast internal conversion from the S₂(¹B_1u, ππ*) state to the S₀ state of benzene were studied using ultrafast extreme-ultraviolet photoelectron spectroscopy and electronic structure calculations. The quantum yield of the internal conversion to the S₀ state reached ∼0.69 in benzene, while lower values of 0.35 and 0.12 were obtained for toluene and o-xylene, respectively. These results indicate that methyl substitution makes the conical intersections less accessible to the nuclear wave packet.

Choline chloride (ChCl) is used extensively as a hydrogen bond donor in deep eutectic solvents (DESs). However, determining its melting properties experimentally is challenging due to decomposition upon melting, leading to widely varying literature values. Accurate melting properties are crucial for understanding the solid-liquid phase behavior of ChCl-containing DESs. Here, we employ molecular dynamics simulations to compute the phase transitions of ChCl, testing a variety of atomistic force fields. We find that the results are sensitive to the choice of force field, but a melting temperature of 627 K and a melting enthalpy of 7.8 kJ/mol seem most reasonable, in good agreement with some literature values. We suggest these as the likely melting properties of ChCl, though the results are tentative due to limited experimental data for the liquid ChCl phase.

Molecular polaritons, the hybridization of electronic states in molecules with photonic excitation inside a cavity, play an important role in fundamental quantum science and technology. Understanding the decoherence mechanism of molecular polaritons is among the most significant fundamental questions. We theoretically demonstrate that hybridizing many molecular excitons in a cavity protects the overall quantum coherence from phonon-induced decoherence. The polariton coherence time can be prolonged up to 100 fs with a realistic collective Rabi splitting and quality factor at room temperature, compared to the typical electronic coherence time which is around 15 fs. Our numerically exact simulations and analytic theory suggest that the dominant decoherence mechanism is the population transfer from the upper polariton state to the dark state manifold. Increasing the collective coupling strength will increase the energy gap between these two sets of states and thus prolong the coherence lifetime. We further derived valuable scaling relations that directly indicate how polariton coherence depends on the number of molecules, Rabi splittings, and light-matter detunings.

We investigated the excited-state dynamics of a conjugated polymer (CP:P3HT)-based ternary hybrid system containing P3HT-coated gold nanoparticles and quantum dots. Transient absorption spectroscopy results revealed that polaron pairs (PPs) originating from nonrelaxed singlet (S₁) excitons of the CP aggregate in the ternary system have shorter electron-hole separation distances than those of PPs in the neat CP aggregate because of the photophysical effects of plasmonic and semiconductor nanocrystals. In particular, the shorter electron-hole distances of PPs led to more back-recombination to S₁ excitons than dissociation into positive polarons in the ternary system, resulting in increased S₁ radiative recombination compared with that in the neat CP system. Thus, the photoluminescence intensity of the CP aggregate in the ternary system increased. Our findings provide new insights into the excited-state dynamics of CPs and pave the way for the development of next-generation high-efficiency optoelectronic devices.

A drift-diffusion model is used to investigate the effect of device degradation on current-voltage and impedance measurements of perovskite solar cells (PSCs). Modifications are made to the open-source drift-diffusion software IonMonger to model degradation via an increasing recombination rate during the course of characterization experiments. Impedance spectroscopy is shown to be a significantly more sensitive measure of degradation than current-voltage curves, reliably detecting a power conversion efficiency drop of as little as 0.06% over a 4 h measurement. Furthermore, we find that fast degradation occurring during impedance spectroscopy can induce loops lying above the axis in the Nyquist plot, the first time this experimentally observed phenomenon has been replicated in a physics-based model.

The restructuring of dilute alloys under gas environments has shown a great impact on their catalytic performance due to intriguing structural sensitivity, but the structural dynamics and underlying mechanism remains elusive. Herein, we directly resolved the distinct dynamic behaviors of PdFe_0.08 dilute alloys under CO or O₂ environment by multidimensional imaging. The stronger binding of gaseous CO with Fe atoms stimulates Fe segregation out of the PdFe_0.08, resulting in 3D growth of Fe islands, whereas the dissociative adsorption of O₂ results in 2D layer-by-layer growth of segregated FeO as encapsulation overlayers that bind strongly with the Pd surface underneath. Such varied structures remarkably tune the catalytic activity for CO oxidation, showing a considerably high activity for a CO-treated sample. Our results reveal the competitive mechanism between adsorbate-metal and metal-metal interaction for gas-induced surface segregation, which should be highly considered for the rational design of dilute alloys with dynamically tuned structure and reactivity.