The Journal of Physical Chemistry A最新文献

The temperature dependence of concerted proton-electron transfer (CPET) reactions of two anthracene-phenol-pyridine (An-PhOH-py) triads is investigated in toluene. Light excitation forms an anthracene local excited state (^1*An), which undergoes CPET to form a charge separated state (CSS, An^•--PhO^•-pyH⁺), which in turn undergoes CPET charge recombination (CR). In toluene, compared with polar solvents, the CSS is energetically destabilized. First, this makes another reaction competitive with CPET, which we propose is proton-coupled energy transfer (PCEnT) from ^1*An to form the short-lived excited state keto tautomer of the phenol-pyridine subunit (*[PhO═pyH]). Second, it puts CR deep into the Marcus inverted region, and CSS lifetimes therefore reach several nanoseconds at room temperature. The slow kinetics makes CR to the anthracene triplet state (^3*An) competitive, as well as another reaction that is strongly activated and dominates CSS deactivation at T ≥ 240 K for one of the triads. The latter is proposed to be CR via initial formation of the same [*PhO═PyH] state as above by an unusual electron transfer (ET) from An^•- to pyH⁺, instead of CR with the juxtaposed PhO^•. The two different pathways to form *[PhO═pyH] lead to CSS yields and lifetimes that vary significantly with temperature, and in markedly different ways between the triads. This is rationalized by the differences in the energies of the states involved. The results broaden the scope and understanding of the still rare phenomena of inverted CPET and PCEnT and may aid toward their use in solar fuels and photoredox catalysis.

The redox mediators help prevent cathode passivation and promote the formation and decomposition of Li₂O₂ within the electrolyte of the battery. Understanding the mechanistic properties of the soluble catalyst from an atomic level is crucial for developing an all-in-one multifunctional soluble catalyst for Li–O₂ batteries. With the help of density functional theory and atom-centered density matrix propagation molecular dynamics simulations, we report how butylated hydroxytoluene (BHT), an experimentally reported soluble catalyst, mediates the stabilization of reactive intermediates and the mechanism behind the formation and decomposition of Li₂O₂. The hydroxy group in BHT facilitates the stabilization of O₂^•– via hydrogen bonding and the solvation of Li⁺, LiO₂^•, and Li₂O₂. This characteristic of BHT helps to promote the solution-phase mechanism and suppress parasitic reactions induced by O₂^•–. During the charging process, the reversibility of BHT and BHT^•+ happens and the disappearance of the hydrogen bonding interaction facilitates the delithiation process. The Mulliken charge distribution analysis shows that the reversibility of BHT and BHT^•+ is due to the electron delocalization between the oxygen atom and benzene ring of BHT. We observe the two benefits of the hydrogen bond: the presence and absence of hydrogen bonding enhance the formation and decomposition of Li₂O_2, respectively. We find that tetraethylene glycol dimethyl ether solvent plays a significant role in stabilizing lithium–oxygen-containing species such as LiO₂^• and Li₂O₂. However, the presence of BHT further improves the results. This finding highlights the cooperative activity of BHT in conjugation with the tetraethylene glycol dimethyl ether solvent. The atom-centered density matrix propagation method reveals that BHT facilitates Li₂O₂ decomposition through protonation, whereas BHT^•+ induces Li₂O₂ decomposition by promoting the formation of LiO₂^• and the BHT:Li⁺ complex without transferring the proton.

The static dipole polarizabilities of group 11 elements (Cu, Ag, and Au) are computed using the relativistic coupled-cluster method with single, double, and perturbative triple excitations. Three types of relativistic effects on dipole polarizabilities are investigated: scalar-relativistic, spin-orbit coupling (SOC), and fully relativistic Dirac-Coulomb contributions. The final recommended values, including uncertainties, are 46.91 ± 1.31 a.u. for Cu, 50.97 ± 1.93 a.u. for Ag, and 36.68 ± 0.78 a.u. for Au. Our results show close agreement with the values recommended in the 2018 table of static dipole polarizabilities for neutral elements [Mol. Phys. 2019, 117, 1200], with reduced uncertainties for Ag and Au. The analysis indicates that scalar-relativistic effects are the dominant relativistic contribution for these elements, while SOC effects are negligible. The influence of electron correlation across all relativistic regimes is also evaluated, demonstrating its significant role in the accurate calculation of dipole polarizabilities.

Graphitic carbon nitride (g-CN) has attracted vast interest as a promising inexpensive metal-free photocatalyst for water splitting with solar photons. The heptazine (Hz) molecule is the building block of graphitic carbon nitride. The photochemistry of the Hz molecule and derivatives thereof in protic environments has been the subject of several recent experimental and computational studies. In the present work, the hydrogen-bonded Hz···H₂O complex was adopted as a model system for the exploration of photoinduced electron and proton transfer processes in this complex with quasi-classical nonadiabatic trajectory simulations, using the ab initio ADC(2) electronic-structure method and a computationally efficient surface-hopping algorithm. The population of the optically excited bright ¹ππ* state of the Hz chromophore relaxes through three ¹nπ* states and a low-lying charge-transfer state, which drives proton transfer from H₂O to Hz, to the long-lived optically dark S₁(ππ*) state of Hz. The imaging of this ultrafast and complex dynamics with femtosecond time-resolved transient absorption (TA) pump–probe (PP) spectroscopy and two-dimensional (2D) electronic spectroscopy (ES) was computationally explored in the framework of the quasi-classical doorway-window approximation. By comparison of the spectra of the Hz···H₂O complex with those of the free Hz molecule, the effects of the hydrogen bond on the ultrafast internal conversion dynamics can be identified in the spectroscopic signals. Albeit the TA PP and 2D ES spectroscopies are primarily sensitive to electronic excited-state dynamics and less so to proton transfer dynamics, they nevertheless can provide mechanistic insights which can contribute to the acceleration of the optimization of photocatalysts for water splitting.

The ground-state spin multiplicity as well as the energy difference between the lowest-energy spin-singlet (S₁) and spin-triplet (T₁) excited states of topologically frustrated organic (diradical) molecules can be tuned by doping with a pair of heteroatoms (N or B atoms). We have thus systematically studied here a set of Clar's Goblet derivatives upon a controlled substitution at different C sites, to alter the electronic structure of the molecules and disclose the positions at which: (i) the ground-state multiplicity becomes a closed-shell singlet and (ii) the energy difference between S₁ and T₁ is considerably small (i.e., below 0.1-0.2 eV to induce a triplet exciton recovery upon thermal effects). This electronic structure outcome is driven by strong correlation effects; therefore, we have here applied a variety of single-reference [TD-DFT, CIS(D), SCS-CC2] and multireference [CASSCF, NEVPT2, RAS-srDFT] methods. For TD-DFT, we have covered global hybrid (PBE0, M06-2X), range-separated hybrid (ωB97X), and double-hybrid (PBE-QIDH, SOS1-PBE-QIDH, and PBE0-2) functionals to ascertain whether the results were highly dependent on the functional choice. Overall, we found that the heterosubstitution strategy could largely modify the electronic and optical properties of the pristine diradical system, with these organic forms thus constituting a new set of compounds with further optoelectronic applications.

In order to explore the effects of high levels of electron correlation on the real-time coupled cluster formalism and algorithmic behavior, we introduce a time-dependent implementation of the CC3 singles, doubles, and approximate triples method. We demonstrate the validity of our derivation and implementation using specific applications of frequency-dependent properties. Terms with triples are calculated and added to the existing CCSD equations, giving the method a nominal $O$(N⁷) scaling. We also use a graphics processing unit accelerated implementation to reduce the computational cost, which we find can speed up the calculation by up to a factor of 13 for test cases of water clusters. In addition, we compare the impact of using single-precision arithmetic compared to conventional double-precision arithmetic. We find no significant difference in polarizabilities and optical-rotation tensor results but a somewhat larger error for first hyperpolarizabilities. Compared to linear response CC3 results, the percentage errors of RT-CC3 polarizabilities and RT-CC3 first hyperpolarizabilities are under 0.1 and 1%, respectively, for a water-molecule test case in a double-ζ basis set. Furthermore, we compare the dynamic polarizabilities obtained using RT-CC3, RT-CCSD, and time-dependent nonorthogonal orbital-optimized coupled cluster doubles (TDNOCCDs) in order to examine the performance of RT-CC3 and the orbital-optimization effect using a set of ten-electron systems.

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) materials have attracted extensive attention due to their 100% exciton utilization efficiency and narrowband emissions. Numerous tube-shaped MR-TADF emitters with full-color narrowband emissions have been reported, and updated molecular design strategies need to be proposed to find more molecular "recipes" to narrow the emission spectral range. Upon changing the shape of the fluorophore from a tubular to fan-shaped structure, the investigated molecules exhibit narrowband emissions based on the analysis of the geometric and electronic structures, reorganization energies, charge transfer characters upon excitation, and absorption and emission properties. The small reorganization energies and short-range charge transfer properties upon excitation are the key to narrowing the spectral range of the molecules. Such theoretical investigations give an in-depth insight into the structure-property relationship, and the updated molecular design strategies would provide important guidance for the design of multiple-resonance molecules with narrowband emissions.

Characterization of the structural and electron transport properties of single chiral molecules provides critical insights into the interplay between their electronic structure and electrochemical environments, providing broader implications given the significance of molecular chirality in chiroptical applications and pharmaceutical sciences. Here, we examined the topographic and electronic features of a recently developed chiral molecule, B,N-embedded double hetero[7]helicene, at the edge of Cu(100)-supported NaCl thin film with scanning tunneling microscopy and spectroscopy. An electron transport energy gap of 3.2 eV is measured, which is significantly larger than the energy difference between the highest occupied and the lowest unoccupied molecular orbitals given by theoretical calculations or optical measurements. Through first-principles calculations, we demonstrated that this energy discrepancy results from the Coulomb interaction between the tunneling electron and the molecule's electrons. This occurs in electron transport processes when the molecule is well decoupled from the electrodes by the insulating decoupling layers, leading to a temporary ionization of the molecule during electron tunneling. Beyond revealing properties concerning a specific molecule, our findings underscore the key role of Coulomb interactions in modulating electron transport in molecular junctions, providing insights into the interpretation of scanning tunneling spectroscopy features of molecules decoupled by insulating layers.

This study deals with the understanding of hydrogen atom scattering from graphene, a process critical for exploring C-H bond formation and energy transfer during atom surface collision. In our previous work [Shi, L.; J. Chem. Phys. 2023, 159, 194102], starting from a cell with 24 carbon atoms treated periodically, we have achieved quantum dynamics (QD) simulations with a reduced-dimensional model (15D) and a simulation in full dimensionality (75D). In the former work, the H atom attacked the top of a single C atom, enabling a comparison of QD simulation results to classical molecular dynamics (cMD). Our approach required the use of sophisticated techniques such as Monte Carlo canonical polyadic decomposition (MCCPD) and multilayer multiconfiguration time-dependent Hartree (ML-MCTDH), as well as further development of quantum flux calculations. We could benchmark our calculations by comparison to cMD calculations. We now refined our method to better mimic experimental conditions. Specifically, rather than sending the H atom to a specific position on the surface, we employed a plane wave for the H atom in directions parallel to the surface. Key findings for these new simulations include the identification of discrepancies between classical molecular dynamics (cMD) simulations and experiments, which are attributed to both the potential energy surface (PES) and quantum effects. Additionally, this study sheds light on the role of classical collective normal modes during collisions, providing insights into energy transfer processes. The results validate the robustness of our simulation methodologies and highlight the importance of considering quantum mechanical effects in the study of hydrogen-graphene interactions.