Excited S1 Research Articles

Pion photoproduction of nucleon excited states with Hamiltonian effective field theory

We refine our previous calculation of multipole amplitude E0+ for pion photoproduction process, γN→πN. The treatment of final-state interactions is based upon an earlier analysis of pion-nucleon scattering within Hamiltonian effective field theory, supplemented by incorporating contributions from the N*(1650) and the KΛ coupled channel. The contribution from the bare state corresponding to the N*(1650) significantly enhances our results. Additionally, we also compute the multipole amplitude M1−, which is of direct relevance to the Roper resonance. The results are comparable with other dynamical coupled-channel models, even though the contribution from the bare state (interpreted as a 2s excitation) in this channel is small because of its large mass. Published by the American Physical Society 2024

Attosecond formation of charge-transfer-to-solvent states of aqueous ions probed using the core-hole-clock technique

Charge transfer between molecules lies at the heart of many chemical processes. Here, we focus on the ultrafast electron dynamics associated with the formation of charge-transfer-to-solvent (CTTS) states following X-ray absorption in aqueous solutions of Na+, Mg2+, and Al3+ ions. To explore the formation of such states in the aqueous phase, liquid-jet photoemission spectroscopy is employed. Using the core-hole-clock method, based on Auger–Meitner (AM) decay upon 1s excitation or ionization of the respective ions, upper limits are estimated for the metal-atom electron delocalization times to the neighboring water molecules. These delocalization processes represent the first steps in the formation of hydrated electrons, which are determined to take place on a timescale ranging from several hundred attoseconds (as) below the 1s ionization threshold to only 20 as far above the 1s ionization threshold. The decrease in the delocalization times as a function of the photon energy is continuous. This indicates that the excited electrons remain in the vicinity of the studied ions even above the ionization threshold, i.e., metal-ion electronic resonances associated with the CTTS state manifolds are formed. The three studied isoelectronic ions exhibit quantitative differences in their electron energetics and delocalization times, which are linked to the character of the respective excited states.

In Search of Covalency Measure of Gd(III)-Ligand Interactions.

Experimental electron density distribution of the [C(NH2)3]3[Gd(EDTA)F2]·H2O crystal was determined. The derived experimental and theoretical (DFT) topological parameters such as ∇2ρc, ρc, bond degree (BD), kinetics, and potential energy were used to study the nature of Gd-O, Gd-F, and Gd-N interactions. The natural charge of the Gd is 1.86; the natural configuration of the cation is [Xe]6s0.134f7.105d0.83, and the covalency of the Gd-L bond is mainly connected with the transfer of charge from the spx ligand orbitals onto the 5d orbitals of the Gd cation. Simultaneously, the donation of charge onto the 6s and 4f orbitals occurs to a lesser extent. Moreover it was found that the donation of the ligand charges onto the Gd(III) is larger for compounds with a lower coordination number. The obtained topological parameters were analyzed in the context of the Gd(III) f-f transition properties, i.e., energy of the excited 2S+1LJ states, Judd-Ofelt intensity parameters, and luminescence lifetimes, of 18 Gd(III) compounds with various O, N, and F donor ligands (DOTA, EDTA, CDTA, DTPA, NTA, EGTA, ODA, F-, H2O, and CO32-). The calculated nephelauxetic β parameter may reflect the penetration degree of electron lone pairs of ligands inside the metal basin. Finally, it was found for the first time that the sum of the Gd(III)-L bond energy (∑EGdL) is correlated with the position of the gravity center of the 8S7/2 → 2S+1LJ transitions and increase of covalency of the Gd(III)-L bonds is associated with decrease of their bond energy. The obtained results may shed light on chemical bonding in systems containing f-elements. Such subtle differences in the covalent contribution to the Ln-L or An-L bond may tune the selectivity of the partitioning processes of lanthanides and actinides.

Wavelength-dependent photoisomerization of trans-4,4′-azopyridine: Nonadiabatic dynamics simulation

The trans–cis photoisomerization processes of 4,4′-azopyridine upon S1 and S2 excitations have been investigated by nonadiabatic dynamics simulations based on multi-reference CASSCF calculations. 119 sampling trajectories were simulated starting from the trans form excited to the S1 (S2) state and the cis-isomer quantum yield is evaluated to be (3 ± 2)% ((18 ± 4)%), which is qualitatively in agreement with the recent experimental results in ethanol. We found that rotation around the central N-N bond accompanied by the N-N-C symmetrical bending vibrations is the main mechanism in photoisomerization of the target molecule excited to the S1 and S2 states. Upon S1 excitation, S1-S0 transition occurs earlier along the C-N-N-C torsional coordinate, leading to a low cis-isomer quantum yield. Upon S2 excitation, half of the simulated trajectories are trapped in a potential well on the S2 state, from which the twisted conical intersections are more easily reached in the internal conversion, resulting in a higher cis-isomer quantum yield.

Ratiometric Chemosensors That Are Capable of Quantifying Hydrostatic Pressure Stimulus: A Case of Porphyrin Tweezers.

Investigating chemosensors that are capable of quantifying pressure in solution, particularly hydrostatic pressure, which is one of the mechanical forces, is an attractive challenge in chemistry from the viewpoint of "mechano"-science. Herein, we report the investigation of chiral porphyrin tweezers, Por-Cy and Por-DPhEt, comprising different flexible linkers; Por-Cy and Por-DPhEt displayed distinct ratiometric signaling by using the higher excited S2 state with a standard excited S1 level. A novel operative mechanism using the S1/S2 fluorescence ratio was revealed using hydrostatic pressure-ultraviolet/visible (UV/vis), fluorescence/excitation, circular dichroism spectroscopy, and lifetime measurements, which can be further controlled by the open-closed conformational change inherent in the tweezer skeleton. Furthermore, the fluorescent chiral tweezers exhibited a promising |g lum| of 2.9 × 10-3, indicating that they are potential candidates for sensory applications in chiral environments. This study provides opportunities for the development of smart pressure-responsive chemosensors.

Solar overall water-splitting by a spin-hybrid all-organic semiconductor

Direct solar-to-hydrogen conversion from pure water using all-organic heterogeneous catalysts remains elusive. The challenges are twofold: (i) full-band low-frequent photons in the solar spectrum cannot be harnessed into a unified S1 excited state for water-splitting based on the common Kasha-allowed S0 → S1 excitation; (ii) the H+ → H2 evolution suffers the high overpotential on pristine organic surfaces. Here, we report an organic molecular crystal nanobelt through the self-assembly of spin-one open-shell perylene diimide diradical anions (:PDI2-) and their tautomeric spin-zero closed-shell quinoid isomers (PDI2-). The self-assembled :PDI2-/PDI2- crystal nanobelt alters the spin-dependent excitation evolution, leading to spin-allowed S0S1 → 1(TT) → T1 + T1 singlet fission under visible-light (420 nm~700 nm) and a spin-forbidden S0 → T1 transition under near-infrared (700 nm~1100 nm) within spin-hybrid chromophores. With a triplet-triplet annihilation upconversion, a newly formed S1 excited state on the diradical-quinoid hybrid induces the H+ reduction through a favorable hydrophilic diradical-mediated electron transfer, which enables simultaneous H2 and O2 production from pure water with an average apparent quantum yield over 1.5% under the visible to near-infrared solar spectrum.

Advancing Triplet Exciton Harvesting Through Heavy Atom Selenium Manipulation in Multiple Resonance Thermally Activated Delayed Fluorescent Emitters

AbstractIn the development of organic light‐emitting diodes (OLEDs) with high efficiency and minimal efficiency roll‐off, fast reverse intersystem crossing (RISC) in multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials is critical. The RISC process is typically hindered by insufficient spin‐orbital coupling (SOC). Incorporating heavy atom selenium into the MR‐TADF structure has the potential to enhance SOC through the heavy atom effect. However, the specific placement of selenium within the molecule results in different enhancements of SOC, with the detailed interplay between these factors yet to be elucidated. The introduction of a selenium‐containing moiety, phenoxaselenine, into the MR‐TADF structure at different substituted positions is undertaken, revealing that the molecule with 3‐substituted phenoxaselenine exhibits faster RISC transition and a significant increase in SOC between higher triplet excited states and S1 state, compared to the molecule with 2‐substituted phenoxaselenine. Significantly reduced efficiency roll‐off is achieved for the narrow‐band emission OLEDs based on the molecule with 3‐substituted phenoxaselenine owing to the enhanced heavy atom effect, giving an impressive external quantum efficiency above 20% even under 10 000 cd m−2 in the corresponding OLED device. These results underscore the potential of strategic heavy atom effect manipulation in MR‐TADF materials for efficient spin‐flipping.

Influence of Selective Carbon 1s Excitation on Auger-Meitner Decay in the ESCA Molecule.

Two-dimensional spectral mapping is used to visualize how resonant Auger-Meitner spectra are influenced by the site of the initial core-electron excitation and the symmetry of the core-excited state in the trifluoroethyl acetate molecule (ESCA). We observe a significant enhancement of electron yield for excitation of the COO 1s → π* and CF3 1s → σ* resonances unlike excitation at resonances involving the CH3 and CH2 sites. The CF3 1s → π* and CF3 1s → σ* resonance spectra are very different from each other, with the latter populating most valence states equally. Two complementary electronic structure calculations for the photoelectron cross section and Auger-Meitner intensity are shown to effectively reproduce the site- and state-selective nature of the resonant enhancement features. The site of the core-electron excitation and the respective final state hole locality increase the sensistivity of the photoelectron signal at specific functional group sites. This showcases resonant Auger-Meitner decay as a potentially powerful tool for selectively probing structural changes at specific functional group sites of polyatomic molecules.

Temperature effect on spectral characters and dipole moment in short-lived excited singlet S1 state of 3HBI-7D-2HChromen-2-one laser dye in non-associative and highly viscous glycerol solvent

Steady state method is employed to study the effect of temperature on the absorption and emission characteristics of 3-(1H-benzo[d]imidazol-2-yl)-7-(diethylamino)-2H-chromen-2-one(3HBI-7D-2HChromen-2-one) laser dye in glycerol solvent. Temperature induces thermal effect on maxima absorption, emission wavelength, fluorescence intensity etc. Radiative and non-radiative transition probabilities mechanism, fluorescence lifetime, frequency assisted parameters decay rate constants, and activation energy is estimated. Advance thermochromic shift method is adopted to determine the ground and excited state dipole moments.

Helium atom embedded in non‐ideal classical plasmas: Doubly excited singlet S states

AbstractThe influence of the non‐ideality (NI) of the classical plasmas on the doubly excited singlet S states of the helium atom (He) embedded in the plasma has been investigated theoretically. A pseudopotential containing the Debye length and the non‐ideality parameter (NIP) as its characteristics is used to represent the screened interaction potentials in the plasma. Using a large wavefunction within the framework of the stabilization method, it has been possible to recognize six doubly excited singlet S states (five lying below the He+(2S) excitation threshold and one lying below the He+(3S) excitation threshold) for the plasma‐free case. The energies and the autoionization life‐times of those states are computed by fitting the density of states to the Lorentzian form. Convergence of the computed results is corroborated by increasing the number of terms in the employed wavefunction. For the plasma‐free case, these results are in excellent agreement with the established results in the literature. A comprehensive analysis has been made on changes induced on those doubly excited states by varying NI over a wide range. It has been observed that the energies of the states gradually approach the corresponding threshold energies with the increasing NI of the plasma, whereas the change in the life‐times (alternatively the widths of the states) of the states shows distinctive features depending on the angular momentum of an individual electron.

TD-DFT analysis of excitation of the closed-form spironaphthopyran in methanol solution: The contribution of vibronic transitions and intermolecular hydrogen bonds

A set of forty hybrid functionals, combined with a 6–31++G(d,p) basis set and an IEFPCM solvent description, was applied to calculate the S0→S1 excitation of the spironaphthopyran (SNP) photochromic compound. None of the hybrid functionals resulted in Cspiro-O bond cleavage upon optimization of the S1 excited state of the SNP, in contrast to the spiropyran BIPS which we studied earlier. At the same time, the deformations of the SNP during excitation turned out to be very small (in contrast to those for BIPS) which made it possible to calculate its vibronic absorption spectrum. The best agreement between the calculated and experimental absorption bands was demonstrated by the SOGGA11X functional. The main result of this work is confirmation of the vibration participation in the breaking of the Cspiro-O bond in the S1 excited state of the SNP. This assumption based on experimental data was previously put forward by other authors. Strong H-bonds between the SNP and two methanol molecules enhance the photoinduced distortions of the latter and are slightly weakened upon excitation.

Shortwave infrared polymethine dyes for bioimaging: ultrafast relaxation dynamics and excited-state decay pathways.

Excited-state relaxation in two prototypical shortwave infrared (SWIR) polymethine dyes developed for bioimaging, heptamethine chromenylium Chrom7 and flavylium Flav7, is studied by means of femtosecond transient absorption with broadband ultraviolet-to-SWIR probing complemented by steady-state and time-resolved fluorescence and phosphorescence measurements. The relaxation processes of the dyes in dichloromethane are resolved with sub-100 fs temporal resolution using SWIR, near-IR, and visible photoexcitation. Different population members of the ground-state inhomogeneous ensemble are found to equilibrate via skeletal deformation changes with time constants of 90 fs and either 230 fs (Chrom7) and 350 fs (Flav7) followed by slower evolution matching the 1-ps timescale of diffusive solvation dynamics. Molecules excited into high-lying singlet electronic states (Sn) by visible excitation repopulate with time constants of 400 fs (Chrom7) and 450 fs (Flav7) the corresponding first excited singlet S1 states, which decay within several hundreds of picoseconds in dichloromethane and chloroform solvents. Vibrational relaxation in S1 for both Chrom7 and Flav7 in dichloromethane occurs with time constants of 350 and 800 fs for excess of vibrational energy of ∼1000 and 10 000 cm-1 deposited by near-IR and visible excitation, respectively. Two competing non-radiative processes are present in S1: temperature-independent internal conversion, and thermally-activated twisting about a carbon-carbon bond of the conjugated chain, which is substantial at room temperature but essentially nonreactive, producing traces of isomer product. Intersystem crossing in S1, and thus the triplet quantum yield, is minor. The importance of absorption bands from the excited S1 state in applications requiring high-intensity excitation conditions is discussed.

Photoswitching of arylazopyrazoles upon S1 (nπ*) excitation studied by transient absorption spectroscopy and ab initio molecular dynamics.

Arylazopyrazoles (AAPs) are an important class of molecular photoswitches with high photostationary states (PSS) and long thermal lifetimes. The ultrafast photoisomerization of four water-soluble arylazopyrazoles, all of them featuring an ortho-dimethylated pyrazole ring, is studied by narrowband femtosecond transient absorption spectroscopy and ab initio molecular dynamics simulations. Upon S1 (nπ*) photoexcitation of the planar E-isomers (E-AAPs), excited-state bi-exponential decays with time constants τ1 in the 220-440 fs range and τ2 in the 1.4-1.8 ps range are observed, comparable to those reported for azobenzene (AB). This is indicative of the same photoisomerization mechanism as has been reported for ABs. In contrast to the planar E-AAPs, a twisted E-AAP with two methyl groups in ortho-position of the phenyl ring displays faster initial photoswitching with τ1 = 170 ± 10 fs and τ2 = 1.6 ± 0.1 ps. Our static DFT calculations and ab initio molecular dynamics simulations of E-AAPs on the S0 and S1 potential energy surfaces suggest that twisted E-isomer azo photoswitches exhibit faster initial photoisomerization dynamics out of the Franck-Condon region due to a weaker π-coordination of the central CNNC unit to the aromatic ligands.

Photoinduced isomerization mechanism of isatin N<sup>2</sup>-diphenylhydrazones molecular switch

Hydrazone molecular switches have significant application value in supramolecular chemistry. A new type of hydrazone molecular switch, named isatin N<sup>2</sup>-diphenylhydrazone, has been synthesized. Owing to its cis-trans isomerization characteristics under visible light excitation, ease of synthesizing of derivatives, and sensitivity to external stimuli, it has important application value in the field of biochemistry. Because of its forward and backward visible light excitation characteristics, it is considered a class of compound that is very suitable for molecular switches, and it has a wide application value in fields such as biotechnology. In addition, the derivatives compound exhibits strong interactions with negative ions, which enhances its function as a molecular switch, making it a four-state molecular switch that can be achieved by a single molecule. However, the photo-induced isomerization mechanism of these new molecular switches is not yet clear, and whether there are novel phenomena in the isomerization process is also unknown. In this work, a semi empirical OM2/MRCI based trajectory surface hopping dynamics method is adopted to systematically study a photo induced isomerization mechanism based on the E-Z isomerization process of the isatin N<sup>2</sup>-diphenylhydrazones molecular switch. Optimization configuration and the average lifetime of the first excited S<sub>1</sub> state are obtained by using the semi-empirical OM2/MRCI method of molecular switch. It is found that the average lifetime of the S<sub>1</sub> excited state of the E-configuration molecular switch is about 107 fs, and the quantum yield of E-Z isomerization of the molecular switch is 16.01%. By calculating the photo induced isomerization process of the molecular switch, two different isomerization mechanisms of the molecular switch are identified. In addition to the traditional molecular switch isomerization mechanism revolving around the C=N bond, a new isomerization mechanism, i.e. the face-to-face twisting of the molecular switch rotor part is elucidated. By calculating the time-resolved fluorescence radiation spectrum, it is predicted that there may be a very fast fluorescence quenching phenomenon occurring in about 75 fs in the isomerization process, slightly faster than the S<sub>1</sub> average decay events (107 fs). The information about wavelength-resolved attenuation at different times is also calculated, which reflects the ultrafast fluorescence quenching process accompanied by fluorescence red shift, ranging from 2.1 × 10<sup>4</sup> cm<sup>–1</sup> to 3.4 × 10<sup>4</sup> cm<sup>–1</sup>. By comparing the calculated fluorescence spectra with the average lifetime of excited states, the existence of “dark states” is proposed, and possible explanations for the existence of “dark states” are provided, and those “dark states” may be related to lower quantum yields. The research results can provide theoretical guidance for the design and application of new molecular switches. The ease of synthesis and sensitivity to external stimuli of its derivatives make those compounds extremely valuable in molecular switching and light measurement applications.

The higher order leaky Lamb wave sensitivity of a notch in a fluid-immersed plate

We present an ultrasonic method of detecting cracks in pipelines based on using normally incident transducers in a pitch-catch setup, which can only excite Lamb modes of higher order than the fundamental modes A0 and S0 commonly used in crack detection applications. By excitation and measurements of the Lamb modes S1, S2, and A3, in a steel plate immersed in fluid with and without a notch (to emulate a crack), the performance of the modes towards crack detection is quantified by assessing whether it returns a high leaky component and whether the notch has a large impact on the leaky component. In order to narrow the scope of measurements necessary to investigate notch sensitivity for different system parameters, and to potentially optimize the system setup, we present a computationally efficient theoretical model based on angular spectrum method (ASM) and the theoretical sensitivity kernel formulation from the field of seismology that accounts for a scatterer in the wave path between the transmitter and receiver. The model is compared against measurements, which show that the frequency components of the S2 mode has both the largest leaky frequency component in the given setup and the largest sensitivity at a frequency close to the maximum leaky frequency such that a difference caused by the notch is easily measured. By using the measurements and the validation calculation as baseline reference, we calculate the expected S2 mode sensitivity and leaky components for larger plate thicknesses and larger standoffs, which exemplifies how the model can be applied in measurement system design and optimization.

Theoretical Study on the Optoelectronic Properties of Merocyanine-Dyes.

Merocyanines, as prototypes of highly polar π-conjugated molecules, have been intensively investigated for their self-assembly and optoelectronic properties, both experimentally and theoretically. However, an accurate description of their structural and electronic properties remains challenging for quantum-chemical methods. We assessed several theoretical approaches, TD-DFT, GW-BSE, STEOM-DLPNO-CCSD, and CASSCF/NEVPT2-FIC for their reliability in reproducing optoelectronic properties of a series of donor/acceptor (D/A) merocyanines, focusing on the first excitation energy. Additionally, we tested an all-electron perturbative method based on time-dependent coupled-perturbed density functional theory, denoted as TDCP-DFT. Particular focus was set on direct and indirect solvent effects, which affect excited-state energies by electrostatic interaction and molecular geometry. The molecular configuration space was sampled at the semiempirical tight-binding level. Our results corroborate previous investigations, showing that the S0 - S1 excitation energy strongly depends on the merocyanine molecular structure and the dielectric constant of the solvent. We found significant effects of the polar solution environment on the geometry of the merocyanines, which strongly affect the calculated excitation energies. Taking these effects into account, the best agreement between calculated and measured excitation energies was obtained with TDCP-DFT and GW-BSE. We also calculated excitation energies of molecular crystals at the TDCP-DFT level and compared the results to the corresponding monomers.

Resonance X(7300): excited 2S tetraquark or hadronic molecule χc1χc1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\chi _{c1}\\chi _{c1}$$\\end{document}?

We explore the first radial excitation X4c∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$X_{\ extrm{4c}}^{*}$$\\end{document} of the fully charmed diquark-antidiquark state X4c=ccc¯c¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$X_{\ extrm{4c}}=cc{\\overline{c}}{\\overline{c}} $$\\end{document} built of axial-vector components, and the hadronic molecule M=χc1χc1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathcal {M}} =\\chi _{c1}\\chi _{c1}$$\\end{document}. The masses and current couplings of these scalar states are calculated in the context of the QCD two-point sum rule approach. The full widths of X4c∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$X_{\ extrm{4c}}^{*}$$\\end{document} and M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathcal {M}}$$\\end{document} are evaluated by taking into account their kinematically allowed decay channels. We find partial widths of these processes using the strong couplings gi∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g_i^{*}$$\\end{document} and Gi(∗)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$G_i^{(*)}$$\\end{document} at the X4c∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$X_{\ extrm{4c}}^{*}$$\\end{document}(M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathcal {M}}$$\\end{document} )-conventional mesons vertices computed by means of the QCD three-point sum rule method. The predictions obtained for the parameters m=(7235±75)MeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m=(7235 \\pm 75)~ \ extrm{MeV}$$\\end{document}, Γ=(144±18)MeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma =(144 \\pm 18)~\ extrm{MeV}$$\\end{document} and m~=(7180±120)MeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\widetilde{m}}=(7180 \\pm 120)~\ extrm{MeV}$$\\end{document}, Γ~=(169±21)MeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\widetilde{\\Gamma }}=(169 \\pm 21)~\ extrm{MeV}$$\\end{document} of these structures, are compared with the experimental data of the CMS and ATLAS Collaborations. In accordance to these results, within existing errors of measurements and uncertainties of the theoretical calculations, both the excited tetraquark and hadronic molecule may be considered as candidates to the resonance X(7300). Detailed analysis, however, demonstrates that the preferable model for X(7300) is an admixture of the molecule M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathcal {M}}$$\\end{document} and sizeable part of X4c∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$X_{\ extrm{4c}}^{*}$$\\end{document}.

Role of Spin Polarization and Dynamic Correlation in Singlet-Triplet Gap Inversion of Heptazine Derivatives.

The new generation of proposed light-emitting molecules for organic light-emitting diodes (OLEDs) has raised considerable research interest due to its exceptional feature─a negative singlet-triplet (ST) gap violating Hund's multiplicity rule in the excited S1 and T1 states. We investigate the role of spin polarization in the mechanism of ST gap inversion. Spin polarization is associated with doubly excited determinants of certain types, whose presence in the wave function expansion favors the energy of the singlet state more than that of the triplet. Using a perturbation theory-based model for spin polarization, we propose a simple descriptor for prescreening of candidate molecules with negative ST gaps and prove its usefulness for heptazine-type molecules. Numerical results show that the quantitative effect of spin polarization decreases linearly with the increasing highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) exchange integral. Comparison of single- and multireference coupled-cluster predictions of ST gaps shows that the former methods provide good accuracy by correctly balancing the effects of doubly excited determinants and dynamic correlation. We also show that accurate ST gaps may be obtained using a complete active space model supplemented with dynamic correlation from multireference adiabatic connection theory.

Channel Competition and Control of Relaxation Pathways in S1 State of Acrolein: Role of Conical Intersection and Surface Crossing.

Channel competition and further photochemical control of relaxation pathways in excited molecules are of primary importance in photochemistry and related areas. Acrolein, as the simplest and most typical α,β-enone, is suitable to provide a model for understanding the photochemistry and photophysics of α,β-enones. Here, the ultrafast dynamics in acrolein following S1(nπ*) excitation has been studied by time-resolved photoelectron imaging (TRPEI) and mass spectroscopy. The competition between intersystem crossing (ISC) and internal conversion (IC) is investigated. The key factor influencing the decay pathways and the relative contributions are revealed to be the position of the excitation relative to the energy of the S1/S0 conical intersection (CI), which is obtained to be 3.65-3.76 eV experimentally. If the excitation is above the CI, IC is superior to ISC and most excited molecules go back to the ground. Otherwise, ISC will dominate the relaxation and lead the triplet products formation. These results show the potential of affecting the dynamics and governing the fate of excited molecules by adjusting the excitation conditions from the point of view of chemical control.

Synthesis and Reactivity of Highly Electron-Rich Zerovalent Group 10 Diborabenzene Pogo-Stick Complexes.

A cyclic alkyl(amino)carbene (CAAC)-stabilized 1,4-diborabenzene (DBB, 1) reacts with the group 10 precursor [Ni(CO)4] to yield the DBB pogo-stick complex [(η6-DBB)Ni(CO)] (2) as a dark-green crystalline solid. The IR-spectroscopic and X-ray crystallographic data of 2 highlight the strong π-donor properties of the DBB ligand. The reaction of 1 with [M(nbe)2] (M = Pd, Pt; nbe = norbornene) yields the unique zerovalent heavier group 10 arene pogo-stick complexes [(η6-DBB)M(nbe)] (3-M), isolated as dark-purple and black crystalline solids, respectively. 3-Pd and 3-Pt show strong near-IR (NIR) absorptions at 835 and 904 nm, respectively. Time-dependent density functional theory (TD-DFT) calculations show that these result from the S0→S1 excitation, which corresponds to a transfer of electron density from a metal d orbital aligned with the z direction (dxz or dyz) to a d orbital located in the xy plane (dxy or dx2-y2), with the redshift for 3-Pt resulting from the higher spin-orbit coupling (SOC). In complex 2, electron donation from the nickel center into the carbonyl 2π* orbital destabilizes the DBB···Ni interaction, resulting in an absorption at a higher energy. Complexes 2 and 3-M react with [Fe(CO)5] to yield the doubly CO-bridged M(0)→Fe(0) (M = Ni, Pd, Pt) metal-only Lewis pairs (MOLPs) 4-M as black (M = Ni, Pt) and dark-turquoise (M = Pd) crystalline solids. Furthermore, 3-Pt undergoes oxidative Sn-H addition with Ph3SnH to yield the corresponding Pt(II) stannyl hydride, [(η6-DBB)PtH(SnPh3)] (5).