The Journal of Physical Chemistry Letters最新文献

Ultrafast time-resolved fluorescence (TRFL) and visible transient absorption (TA) measurements were performed to investigate excited-state dynamics of several electron donor–acceptor complexes (DACs) following charge-transfer (CT) excitation in solution. For all DACs studied, including benzene–tetracyanoethylene (BZ–TCNE), toluene–TCNE, fluorobenzene–TCNE, and (BZ)₂–TCNE, the CT-state lifetimes obtained from TRFL are consistently shorter than those from TA by factors of ∼2–5. This disparity, together with fluorescence lifetimes of ∼5–30 ps in dichloromethane, cannot be reconciled with the conventional assumption that CT excitation initially yields only emissive tight ion pairs (TIPs). The results instead support a revised concurrent mechanism in which CT excitation generates a locally hot and structurally diverse ion-pair ensemble that bifurcates into parallel relaxation pathways, leading to fluorescent TIPs and nonfluorescent loose ion pairs. The two species undergo independent charge recombination at different rates, yielding the distinct lifetimes observed in the TRFL and TA measurements.

In the metal porphyrin-based electrocatalysts for oxygen reduction reaction (ORR), unraveling the electronic effect in different levels of coordination sphere of central metal ions is appealing to boost their intrinsic catalytic performance. To understand the long-range electronic effect, herein, we synthesize four cobalt porphyrin molecules featuring electron-donating/withdrawing substituents located in the third coordination sphere, and then, we π-π stack them onto three-dimensional nitrogen-doped graphene/carbon nanotubes (N-G/CNTs). The results demonstrate that the N-G/CNTs carrier orientates the macrocyclic planarity of porphyrin molecules for the extended π-conjugation, by which electron-donating substituents can substantially drive electron accumulation around the Co–N₄ centers. Consequently, electron density of intrinsic Co–N₄ centers is efficaciously compensated and spin crossover of Co²⁺ ion is induced from low spin to high spin states, as to optimize the absorption/desorption of reactive intermediates and lower the reaction energy barriers. The resultant Co-tetra(methoxyphenyl)porphyrin stacked on the N-G/CNTs has the best ORR catalytic performance. An assembled Zn-air battery showcases a peak power density of 151 mW cm^–2, a specific capacity of 807 mAh g^–1, and an outstanding charge/discharge cycle stability of more than 300 cycles, outlining the promising alternative to the Pt/C-based Zn-air battery.

Ion migration is a key phenomenon that influences the performance and stability of metal halide perovskite solar cells (PSCs). In this work, we systematically study how ion mobility evolves under thermal stress at 85 °C, using capacitance–frequency (C–f) spectroscopy measured in the dark. Aided by drift-diffusion simulations, we demonstrate that the measured C–f spectra cannot be reproduced using a single anion density with a unique ion mobility, particularly in the low-frequency domain where nonideal behavior emerges. A double-Gaussian distribution of anion mobilities provides a substantially better fit even for fresh devices and remains necessary after prolonged aging under thermal stress. This evolution suggests that heat stress not only influences the redistribution of mobile ions but also induces morphology-related changes, such as interface modifications and interlayer degradation, which collectively alter the electrochemical response of the device. Furthermore, the experimental hysteresis index (HI) for fresh and aged devices cannot be captured by assuming a single ion mobility, indicating that a distribution of ion mobilities is necessary to fully describe hysteresis behavior. These findings elucidate the complex ion dynamics under thermal stress and point toward the presence of distinct ionic populations contributing to device behavior, with implications for improving PSC stability.

Photocatalytic conversion of CO₂ to renewable hydrocarbon fuels provides a sustainable avenue for mitigating the global greenhouse effect and the energy shortage crisis. However, the development of highly efficient CO₂ photoreduction catalysts remains a substantial challenge due to the weak light absorption, rapid carrier recombination, and inefficient active site. Herein, we suggest a plasmonic silver-deposited Bi₅O₇I photocatalyst synthesized via combination approaches of wet chemical and solid-state reaction methods, achieving an enhanced CO evolution rate of 23.01 μmol g^–1 h^–1 under simulated solar light without any sacrificial agents. Mechanism analysis indicated that the enhanced activity originates from the localized surface plasmon resonance effect and plasmonic metal/semiconductor junction, which can trigger stronger visible light absorption and facilitate the separation of photogenerated carriers. Moreover, the metal/semiconductor interface can provide highly efficient active sites to significantly enhance the adsorption capability of reaction intermediates and smooth the Gibbs free energy profiles, ultimately leading to superior photocatalytic CO₂ reduction (PCR) activity. To summarize, this work delivers an efficient strategy to achieve the simultaneous improvement of light absorption, carrier dynamics, and surface reaction and ultimately promote the PCR performance.

Electric dipoles are ubiquitous, and they are unequivocally important for vital processes in nature and in manmade devices. A recent examination of the dipole dynamics of molecular electrets (i.e., macromolecules with ordered electric dipoles) reveals enormous picosecond fluctuations ranging from 50% to 200% of the average magnitudes. Herein, we demonstrate their universality by exploring the dipole dynamics of aromatic molecules by using polarizable molecular dynamics and quantum mechanical calculations. Explicit solvent implementation leads to not only large fluctuations of the dipoles of polar species, such as coumarin 102, but also the emergence of fluctuating dipoles of nonpolar polycyclic aromatic hydrocarbons (PAHs), such as pyrene and pentacene. For the nonpolar PAHs in polar solvents, the magnitude of the dipole transients reaches up to 5 D. These results demonstrate key paradigms of fluctuating localized electric fields emerging from solvation dynamics with major implications for charge transfer, catalysis, energy conversion, and enzymatic transformations, among other phenomena.

Organic molecular crystals have gained significant research attention in recent years due to their intriguing photophysical properties and potential applications in photovoltaic and emissive devices. This growing interest has amplified the need for accurate and robust computational protocols to investigate their photophysical behavior. In this work, we present multiscale computational strategies designed to model the shape and broadening of UV–vis absorption spectra in organic crystalline materials. These protocols enable a quantitative assessment of spectral broadening originating from various sources in typical crystalline polyacenes. Adopting an ab initio approach, we employ self-consistent microelectrostatic embedding and Ewald-based ONIOM models to incorporate structural features and environmental effects as well as contributions from static disorder, excitonic coupling, and vibronic interactions. The developed protocols successfully quantify the spectral broadening, as demonstrated for naphthalene and anthracene crystals. This framework is broadly applicable and offers a reliable foundation for the investigation of a wide range of organic molecular crystals, enabling detailed studies of diverse fluorophores and systems of photophysical relevance.

Precise characterization of the graphene–water interface has been hindered by the experimental inconsistencies and limited molecular-level access to interfacial structures. In this work, we present a novel integrated computational approach that combines machine-learning-driven molecular dynamics simulations with first-principles vibrational spectroscopy calculations to reveal how graphene oxidation alters the interfacial water structures. Our simulations demonstrate that pristine graphene leaves the hydrogen-bond network of interfacial water largely unperturbed, whereas graphene oxide (GO) with surface hydroxyls induces a pronounced Δν̃ ≈ 100 cm^–1 redshift of the free OH vibrational band and a dramatic reduction in its amplitude. These spectral shifts in the computed surface-specific sum-frequency generation spectrum serve as sensitive molecular markers of the GO oxidation level, reconciling previously conflicting experimental observations. By providing a quantitative spectroscopic fingerprint of GO oxidation, our findings have broad implications for catalysis and electrochemistry, where the structuring of interfacial water is critical to the performance.

The search for quantum phenomena in quantum dots and related quantum materials is ultimately limited not by synthesis but by measurement precision. Ultrafast spectroscopy remains the tool of choice for revealing these effects, yet progress is often constrained by inadequate temporal resolution, poorly defined initial states, and unrecognized artifacts. In this Perspective, discovery follows precision. Time-resolved photoluminescence demonstrates how improving the instrument response from the nanosecond to the picosecond regime transforms multiexciton recombination from invisible background into resolved physical dynamics. Transient absorption illustrates the necessity of state-resolved pumping: resonant excitation with dual tunable optical parametric amplifiers replaces the common 3.1 eV convenience pump, producing well-defined excitonic populations that expose excited-state absorption and hot-exciton cooling pathways. Finally, coherent multidimensional spectroscopy represents a qualitative leap, resolving correlations and coherences that reveal exciton–polaron coupling at the system–bath level. Across these methods, sharper resolution, state selectivity, and artifact control consistently uncover new physics. The frontier in quantum materials lies in precision measurement itself─where rigor becomes the engine of discovery.

Organic synaptic devices with environmental stability are important for the development of smart electronic systems. However, there are challenges in preparing air-stable synaptic devices due to the sensitivity of organic semiconductors to moisture and oxygen. Here, poly(3-hexylthiophene)-block-poly(phenyl isocyanide) with pentafluorophenyl ester (P3HT-b-PPI(5F)), which combines both carrier transport and charge trapping functions, was selected to be blended with poly(methyl methacrylate) (PMMA) to prepare synaptic devices. Vertical phase separation was generated after deposition of the blended solution, enabling one-step preparation of the active and encapsulated layers of the device. P3HT-b-PPI(5F) and PMMA are the device active layer and encapsulation layer, respectively. The synaptic device has high stability, with the postsynaptic current remaining above 90% after 2 weeks in air. Basic synaptic behavior was successfully simulated under green light stimulation. The energy consumption of a single synaptic event can be as low as 0.6 fJ after reducing the operating voltage. Further, high-pass filtering and optical decoding of “Morse code” were simulated. In addition, biomimetic visual learning and forgetting behaviors were simulated. This work demonstrates a method for preparing air-stable synaptic devices with potential applications in the field of bionic electronics.