The Journal of Physical Chemistry A最新文献

Predictingand rationalizing the singlet oxygen (¹O₂) photosensitizationefficiency of Re(I) tricarbonyl complexesremains challenging due to the complex interplay of electronic andenvironmental factors. In this work, we employ Density FunctionalTheory (DFT) and Conceptual DFT (C-DFT) analysis to systematicallyrationalize the substituent- and solvent-dependent sensitization trendsof a family of pyrazolyl–pyridazine fac-Re(I)(CO)₃Br complexes. While the global quantum yields (Φ_Δ) initially exhibited an unintelligible verticaldispersion in high-polarity media when plotted against the electronicdescriptors, a rigorous mathematical deconstruction into triplet quenchingefficiency (P^T) and the fraction of productiveenergy transfer (f^T)successfully unraveled the underlying photophysics. In non-proticenvironments (benzene, dichloromethane, and acetonitrile), the systemsadhere to a conventional diffusion-controlled dynamic quenching regimesuccessfully mirrored by continuous-dielectric C-DFT indices─specificallythe global electrophilicity (ω) and the rheniumcontribution to the HOMO (% Re). In contrast, analyzing these relationshipsin dimethylformamide and ethanol revealed an “unphysical”regime in which f^T approaches2 or dynamic quenching fails (P^T = 0)yet significant ¹O₂ generation is detected.This mathematical divergence provides compelling diagnostic proofof a solvent-induced mechanistic switch toward ground-state staticaggregates or upper-precursor-mediated pathways. These results highlightthat the boundaries where continuous computational models collapsecan serve as a diagnostic tool to map specific solute-solvent interactions,providing new principles for designing high-efficiency transition-metalphotosensitizers.

We develop a robustalgorithm for locating bound states in coupled-channelcalculations. Bound states exist at energies where an individual eigenvalueof a log-derivative or ratio matching matrix passes through zero.We describe an algorithm to identify the required eigenvalue of thematching matrix over the full range of energy where it exists. Thisallows much simpler programming than previous methods. We also considerthe choice of the matching distance R_match, where the matching matrix is defined; coupled-channel methods aremost efficient if R_match is chosen tobe in the classically allowed region for all channels that supportbound states of interest, but not very close to a node in the wavefunction.

Simulating photodissociationbecomes challenging when the numberof states involved grows large. The computational complexity is usuallyreduced by restrictions that limit the model’s scope. We presenta first-principles quantum model for strong-field photodissociationthat treats rotational dynamics explicitly. The random-phase thermalwavefunction method reduces the large computational cost. The simulationyields experimental observables, such as the momentum angular distributionof the photofragments. We study how these observables converge attwo field intensities, with each set at a different temperature. Themethod is designed to reach conditions where exact numerical methodsbecome intractable; here, we validate it against exact results inthe regime where both are available. Beyond the conventional dependenceon system size and number of realizations, we find that convergencedepends on the observable’s sensitivity to coherence.

Metal-free triplet–tripletannihilation upconversion(TTA-UC)under long-wavelength excitation rules out metal toxicity and improvesbiocompatibility, showing great potential for biomedical use of photonupconversion materials. Intermolecular hydrogen bonding commonly occursin biological environments, yet its effects on organic upconversionperformance have rarely been clarified. Herein, we present a cationicNile blue derivative (SeNB) as an effective sensitizer that producesfar-red to visible upconversion luminescence, and adopt this moleculeas a model to explore hydrogen-bonding impacts on organic upconversion.Transient electronic spectroscopy measurements show solvent hydrogenbonding weakens upconversion by disrupting excited states of boththe sensitizer and annihilator, and by slowing intermolecular tripletenergy transfer via the solvent cage effect. Such interactions directlyquench the triplet state of SeNB, greatly reducing intersystem crossingrates and triplet quantum yields. The diketopyrrolopyrrole (DPP) annihilatorcarries hydrogen-bond accepting sites, and undergoes accelerated tripletquenching and shortened triplet lifetimes under hydrogen-bonding interactions.At low annihilator content, solvent cage effects driven by hydrogenbonding hinder Dexter-type triplet energy transfer from the sensitizerto the annihilator, which further lowers upconversion efficiency.This study demonstrates that Nile blue derivatives are effective sensitizersfor TTA-UC, but also reveals that intermolecular hydrogen bondingseverely suppresses their upconversion performance in protic solvents.These findings provide fundamental insights into solvent-regulatedphotophysical behaviors of ionic sensitizers and highlight the needfor molecular engineering strategies to mitigate hydrogen-bondingeffects for future applications in biological environments.

Polycyclic aromaticnitrogen heterocycles (PANHs) represent anintriguing class of prebiotic molecules whose cosmic origins remainpoorly understood. While there have been detections of several PANHsin carbonaceous meteorites, their apparent absence in the interstellarmedium, where their pure carbon counterparts are widespread, raisesintriguing questions regarding their formation and destruction pathways.Here, we present the laboratory rotational spectroscopy and astronomicalsearch for all seven isomers of the cyanoisoquinoline (isoquinolinecarbonitrile)PANH family toward the dense core of the cold dark cloud TMC-1 usingobservations from the GOTHAM spectral line survey. We report nondetectionsfor all seven isomers and upper limits on their column densities.We then discuss potential formation pathways, including the formationof isoquinoline through bottom-up, top-down, and grain-surface icechemistry processes, followed by the addition of CN to isoquinoline.The nondetection of these species may reflect observational challengessuch as the dilution of signal across isomers, or it may point todifferences in the formation and destruction pathways of PANHs comparedto PAHs. These findings illustrate the complexity of PANH formationand emphasize the need for continued investigation into the processesthat link the organic material present in interstellar and meteoriticenvironments.

Nitrousoxide (N₂O) and ethylene (C₂H₄) blendingfuel is one of the most representative nitrousoxide fuel blend propellants. To address deficiencies in the studyof the C₂H₄/N₂O model at intermediatetemperatures, this work investigates the C₂H₄ + N₂O potential energy surface using quantum chemistryat the CCSD(T)/aug-cc-pVQZ//B3LYP/6-311++G(d,p) level. Rate constantsover 333–2000 K and 0.1–100 atm are calculated basedon RRKM/ME theory. According to our calculation results, the additionreaction C₂H₄ + N₂O → CH₂CH₂N₂O is identified as the dominantchain-initiation step under the present investigated conditions, whichdecomposes via two primary pathways. The CH₂CH₂N₂O → CH₂O + CH₂NN pathwaycompetes strongly with the CH₂CH₂N₂O → CH₃CHO + N₂ channel due to theirclose energy barriers. Well-skipping reactions of C₂H₄ + N₂O → CH₃CHO + N₂ and C₂H₄ + N₂O → CH₂O + CH₂NN, as well as a newly computed pathwayCH₂NN → CH₂ + N₂, are alsoimportant under combustion-relevant conditions. These obtained reactionpathways and their related rate constants are incorporated into fourdifferent models, i.e., GRI 3.0 model, Konnov 2009 model, Glarborg2018 model, and Zhang 2023 model. The updated reactions significantlyimprove all their predictions of ignition delay times at intermediatetemperatures. The impact of the theoretical calculation results onthe mechanism of N₂O/C₂H₄ oxidationis analyzed. At intermediate temperatures, chain-initiation reactionsbetween N₂O and C₂H₄ successfullybypass the unimolecular decomposition of N₂O that requireshigh activation energy. Therefore, C₂H₄ tendsto react directly with N₂O, and aldehyde-related reactionsare responsible for chain propagation and OH formation. In contrast,at high temperatures, the decomposition of N₂O is activated,and the reactions between C₂H₄ and reactiveradicals become another important pathway for fuel consumption. Consequently,the contribution of the direct reaction between C₂H₄ and N₂O is weakened.

Femtosecond pulse excitation gave the time evolutionof the transientabsorption spectra (TAS) of trans- and cis-stilbene (t- and c-St) in methanol.Global analysis of t-St TAS gives the spectrum ofthe singlet excited state of t-St, ¹t*, with a lifetime, 46 ps, consistent with previous measurements.The spectrum of the singlet excited state of c-St, ¹c*, has bands at 360 and 630 nm in agreementwith early literature spectra in other solvents. However, the ¹c* spectrum obtained on multiexponentialglobal analysis of c-St TAS is much more intensein the UV relative to the visible in disagreement with the observedTAS. Although the lifetime of the 630 nm band, 0.47 ps, agrees withthe reported lifetimes, monoexponential fits in the UV region yieldlifetimes that are significantly longer. We attribute this discrepancyto interference by the twisted phantom singlet, ¹p*, whose growth and decay occur in the same UV region.The 360 nm band rises together with a weak 405 nm band that decaysfaster and may be the Franck–Condon ¹c* transient or a ¹c* transient on theway to dihydrophenanthrene formation. Also observed on exciting c-St is the TAS of ¹t*. A mechanisminvolving two-photon sequential excitation of c-Staccounts for this result.

Enantiorecognitionis conventionally rationalized throughstereochemicalmodels, such as lock-and-key, induced-fit, and three-point interactionschemes, in which a chiral selector discriminates between enantiomersthrough geometry and noncovalent interactions. Nevertheless, suchmodels are blind to electron spin. Chiral-induced spin selectivity(CISS) brings electron spin explicitly into this picture. Here, weargue that spin-selective charge transfer can provide an additional,predominantly kinetic contribution to enantiorecognition, most clearlyexpressed out of equilibrium, where it affects adsorption, reaction,or charge-transfer rates. We organize this view as a generator-and-readerscheme: a chiral element under a nonequilibrium drive generates ahandedness-locked spin polarization, which is then read either bya ferromagnet, through exchange, or by a second chiral element, throughspin matching, with no external magnet required. Recent experimentson magnetic adsorption, electrochemical junctions, organic photoelectrochemicaltransistors, and magnetization-controlled growth of helical aggregatesfrom achiral units converge on this generator-and-reader structure.Across these platforms (spanning molecular, axial, and emergent mesoscopicchirality), a common signature recurs: a handedness-dependent, spin-selectivecurrent at a chiral charge-transfer interface. Rather than replacingstereochemical models, this framework adds a spin-resolved electroniccoordinate to them: one that becomes experimentally visible when chiralrecognition is coupled to nonequilibrium charge transfer.

Superthermal (“hot”) oxygen atoms deposittheir energyin planetary upper atmospheres and in hypersonic shock layers throughcollisions with N₂, but the rate at which they do so isset not by the magnitude of the collision cross section, which isdominated by forward diffraction, but by transport-weighted momentsof the differential cross section (DCS). We derive momentum-transferand viscosity cross sections, mean collisional deflections, and energy-relaxationrates for O(³P) + N₂ from our previously reportedquantum coupled-channel DCSs, for ¹⁶O, ¹⁷O,and ¹⁸O over collision energies 0.31–4.0 eV. Themomentum-transfer cross section is well represented by σ_m = 9.90 × 10^–16E_k^–0.385 cm² (E_k in eV), a factor of 28–32 below the collisioncross section, with mean deflection ⟨1 – cos θ⟩= 0.031–0.036. Rotationally inelastic channels supply 72–88%of it, so transport treatments built on elastic angular distributionsunderestimate the stopping power of N₂ several-fold. Theheavy-isotope enhancement of the integral elastic cross section (1–5%)does not survive transport weighting. σ_m is isotope-independentto within 0.4% above 0.6 eV, because the enhancement resides in thetransport-inert forward cone, so isotopic effects in thermalizationare kinematic (+2.9% recoil per collision for ¹⁸O relativeto ¹⁶O). The mean energy loss per collision rises from10 to 68 meV, and Monte Carlo slowing down gives ≈120 collisionsand a stopping column of 3.7 × 10¹⁵ cm^–2 to thermalize a nascent 3.48 eV atom in pure N₂, some20 times the isotropic hard-sphere estimate. A loss law that satisfiesdetailed balance in a 460 K bath raises the number of collisions by6.5%. Comparing the isotopes at equal velocity instead of equal energyshifts σ_m by 1.5–2.8%, and this shift is purelykinematic.

In hydrocarbon fuel oxidation, propanal is a key intermediateandoxygenated pollutant. Its combustion rate constants are mostly estimatedby analogy, bringing large uncertainties to kinetic models. This workcomprehensively investigates H-abstraction from propanal by H/CH₃/C₂H₅/OH radicals. High-precision rateconstants and branching ratios were determined by multistructuralvariational transition state theory with small-curvature tunnelingacross 240–2000 K. Our findings emphasize that conformationalflexibility and torsional anharmonicity greatly affect both the rateconstants and branching ratios. Across the full temperature range,α-site abstraction (R1α) is the primary process in thepropanal + H system. For propanal + CH₃, the rate constantof β-site channel (R2β) is dominant. In the propanal +C₂H₅ system, the α-site reaction (R3α)remains prominent, whereas for propanal + OH, the branching ratiosof the β-site and γ-site channels (R4β, R4γ)increase with temperature, while that of the α-site (R4α)decreases. Excellent agreement with available experimental data isachieved by the fitted expression k_R4 = 0.0017 × T^4.835 exp(2621.61/T) (in cm³ mol^–1 s^–1) for the total rate constant of propanal + OH. The new rate constantswere adopted to update Veloo et al.’s kinetic model, followedby sensitivity analysis. The revised model enables more reliable simulationof propanal combustion and emission behaviors.