Lowest Excited State Research Articles

Varying primordial state fractions in exo- and endothermic SIDM simulations of Milky Way-mass haloes

Abstract Self-interacting dark matter (SIDM) is increasingly studied as a potential solution to small-scale discrepancies between simulations of cold dark matter (CDM) and observations. We examine a physically motivated two-state SIDM model with both elastic and inelastic scatterings. In particular, endothermic, exothermic, and elastic scattering have equal transfer cross sections at high relative velocities (vrel ≳ 400 km s−1). In a suite of cosmological zoom-in simulation of Milky Way-size haloes, we vary the primordial state fractions to understand the impact of inelastic dark matter self-interactions on halo structure and evolution. In particular, we test how the initial conditions impact the present-day properties of dark matter haloes. Depending on the primordial state fraction, scattering reactions will be dominated by either exothermic or endothermic effects for high and low initial excited state fractions respectively. We find that increasing the initial excited fraction reduces the mass of the main halo, as well as the number of subhaloes on all mass scales. The main haloes are cored, with lower inner densities and higher outer densities compared with CDM. Additionally, we find that the shape of the main halo becomes more spherical the higher the initial excited state fraction is. Finally, we show that the number of satellites steadily decreases with initial excited state fraction across all satellite masses.

Fine tuning of excited states by trifluoromethylphenyl for blue-shifted color and enhanced EQEs in thermally activated delayed fluorescence emitters

3,6-di-tert-butyl-9H-carbazole and 3,6-diphenyl-9H-carbazole have been widely used to construct blue thermally activated delayed fluorescence (TADF) emitters. However, it is difficult for related emitters to achieve maximum external quantum efficiency (EQEmax) above 20 % with the Commission Internationale de l'Eclairage (CIE) y ≤ 0.12. A new type of donor was developed to construct blue TADF molecules, namely CF3P-BuCz-TRZ and CF3P-PhCz-TRZ. The weak electron-withdrawing trifluoromethylphenyl (CF3P) with moderate steric hindrance was introduced into the 1-site of carbazole donor for improving the color purity for blue TADF emitters. More importantly, the introduction of CF3P tightly compacts the energy levels for the significant excited states in RISC process. The energy gap between the lowest singlet excited (S1) state and the lowest triplet (T1) state (Δ E(S1−T1)), as well as between T1 and the higher triplet (Tn, n ≥ 2) states (Δ E(Tn−T1)) were reduced, so that Tn (n ≥ 2) could be effectively harvested to further promote reverse intersystem crossing (RISC). As a result, the OLEDs based on CF3P-BuCz-TRZ and CF3P-PhCz-TRZ displayed blue electroluminescence with CIE coordinates of (0.156, 0.107) and (0.155, 0.115). In particular, the maximum EQEs of the CF3P-PhCz-TRZ device reached 20.43 % without employing any light out-coupling enhancement or TADF-sensitized structure. This strategy should be valuable for designing more pure-blue and deep-blue TADF emitters.

Broken seniority symmetry in the semimagic proton mid-shell nucleus Rh95

Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research () Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian. Published by the American Physical Society 2024

Photophysical Studies of a Zr(IV) Complex with Two Pyrrolide-Based Tetradentate Schiff Base Ligands.

The reaction of two equivalents of N,N'-bis(2-pyrrolylmethylidene)-1,2-phenylenediamine (H2bppda) with tetrabenzylzirconium provided the air- and moisture-stable eight-coordinate complex Zr(bppda)2. Temperature-dependent steady-state and time-resolved emission spectroscopy established weak photoluminescence (ΦPL = 0.4% at 293 K) by a combination of prompt fluorescence and thermally activated delayed fluorescence (TADF) upon visible light excitation at and around room temperature. TADF emission is strongly quenched by 3O2 and shows highly temperature-sensitive emission lifetimes of hundreds of microseconds. The lifetime of the lowest energy singlet excited state, S1, was established by transient absorption spectroscopy and shows rapid deactivation (τ = 142 ps) by prompt fluorescence and intersystem crossing to the triplet state, T1. Time-dependent density functional theory (TD-DFT) calculations predict moderate ligand-to-metal charge transfer (LMCT) contributions of 25-30% for the S1 and T1 states. A comparison of Zr(bppda)2 to related zirconium pyridine dipyrrolide complexes, Zr(PDP)2, revealed important electronic structure changes due to the eight-coordinate ligand environment in Zr(bppda)2, which were correlated to differences in the photophysical properties between the two compound classes.

Multi-state vibronic dynamics of the benzene cation: Combined multi-mode Jahn-Teller and Pseudo Jahn-Teller Effects

The multi-state vibronic interactions in the benzene radical cation are investigated theoretically, based on an ab initio quantum dynamical approach. The three lowest doubly degenerate and two lowest non-degenerate electronic states are included, amounting to eight electronic component states and 28 vibrational degrees of freedom. The multi-mode dynamical Jahn-Teller as well as pseudo Jahn-Teller effects are included on an equal footing. This becomes possible by employing the Multiconfigurational Time-Dependent Hartree Method and its multi-layer extension for the wavepacket propagation underlying the dynamical treatment. The results indicate a step wise population transfer from higher to lower-energy electronic states. The transfer between the highest ( E∼ and D∼ states) is extremely fast which is made plausible by their energetic proximity. On the other hand the transfer is not complete and does not comprise the X∼ ground state. Rather, a substantial part of the population gets trapped in the lowest excited ( B∼ ) state. The phenomenon is briefly discussed and calls for future work on this intricate dynamical system.

Inversion isomerism induced by the Pseudo Jahn-Teller Effect in X2CE molecules (X = H, F; E = O, S, Se) in their reduced and excited states

The pseudo-Jahn-Teller effect (PJTE) is employed to reveal the origin of molecular geometry changes induced by reduction and excitation, using a series of X2CE molecules (X = H, F, Cl; E = C, S, Se) as examples. Their nuclear configuration is planar with C 2v symmetry in the ground electronic state. However, when reduced, they acquire a nonplanar pyramidal structure with an elongated C-E bond in their ground and lowest excited electronic states 1A2 and 3A2. It is shown that these distortions are due to the PJT mixing of the reference electronic states with appropriate excited states via the b 1 vibrational mode. The PJTE is shown to reasonably parametrize the adiabatic potential energy curve ε(Qb 1) along the instability coordinate Qb 1.

Excited-state properties of Cu-TADF complexes: A density functional theory study

Organometallic complexes, including copper atom, have attracted great interest as thermally activated delayed fluorescence (TADF) emitters for light emitting diode (LED) applications. This is ascribed to the potential low-cost, abundant availability of copper and most importantly to the ability of copper to enhance the spin–orbit couplings and, consequently, increase the reverse intersystem crossing rates. In this article, we use density functional theory (DFT) to investigate the excited state properties of six copper complexes based on N-heterocyclic carbene ligand, monoamido-amino carbene and diamido carbene, and carbazole ligand. The DFT calculations show that the lowest excited states consist of three groups, i.e., (i) local carbazole excitations, (ii) carbazole-to-carbene intramolecular charge transfer states, and (iii) metal-to-ligand charge transfer states. Only the latter states are characterized with large spin–orbit couplings. The DFT calculations show that the surrounding medium could have a major effect on electronic spectrum by reordering the states. Our results suggest that the TADF properties of the investigated complexes can be affected by the chemical structure of the ligands as well as by the dielectric properties of the LED device active layer.

First-principles design of heavy-atom-free singlet oxygen photosensitizers for photodynamic therapy.

In photodynamic therapy (PDT) treatment, heavy-atom-free photosensitizers (PSs) are a great source of singlet oxygen photosensitizer. Reactive oxygen species (ROS) are produced by an energy transfer from the lowest energy triplet excited state to the molecular oxygen of cancer cells. To clarify the photophysical characteristics in the excited states of a few experimentally identified thionated (>C=S) molecules and their oxygenated congeners (>C=O), a quantum chemical study is conducted. This study illustrates the properties of the excited states in oxygen congeners that render them unsuitable for PDT treatment. Concurrently, a hierarchy is presented based on the utility of the lowest-energy triplet excitons of thionated compounds. Their non-radiative decay rates are calculated for reverse-ISC and inter-system crossover (ISC) processes. In addition, the vibronic importance of C=O and C=S bonds is clarified by the computation of the Huang-Rhys factor, effective vibrational mode, and reorganization energy inside the Marcus-Levich-Jörtner system. ROS generation in thionated PSs exceeds their oxygen congeners as kf ≪ kISC, where radiative decay rate is designated as kf. As a result, the current work offers a calculated strategy for analyzing the effectiveness of thionated photosensitizers in PDT.

Probing the electronic structure and ground state symmetry of gas phase C60+ via VUV photoionization and comparison with theory.

Recently, some of us reviewed and studied the photoionization dynamics of C60 that are of great interest to the astrochemical community as four of the diffuse interstellar bands (DIBs) have been assigned to electronic transitions in the C60+ cation. Our previous analysis of the threshold photoelectron spectrum (TPES) of C60 [Hrodmarsson et al., Phys. Chem. Chem. Phys. 22, 13880-13892 (2020)] appeared to give indication of D3d ground state symmetry, in contrast to theoretical predictions of D5d symmetry. Here, we revisit our original measurements taking account of a previous theoretical spectrum presented in the work of Manini et al., Phys. Rev. Lett. 91(19), 196402 (2003), obtained within a vibronic model parametrized on density functional theory/local-density approximation electronic structure involving all hg Jahn-Teller active modes, which couple to the 2Hu components of the ground state of the C60+ cation. By reanalyzing our measured TPES of the ground state of the C60 Buckminsterfullerene, we find a striking resemblance to the theoretical spectrum calculated in the work of Manini et al., Phys. Rev. Lett. 91(19), 196402 (2003), and we provide assignments for many of the hg modes. In order to obtain deeper insights into the temperature effects and possible anharmonicity effects, we provide complementary modeling of the photoelectron spectrum via classical molecular dynamics (MD) involving density functional based tight binding (DFTB) computations of the electronic structure for both C60 and C60+. The validity of the DFTB modeling is first checked vs the IR spectra of both species which are well established from IR spectroscopic studies. To aid the interpretation of our measured TPES and the comparisons to the abinitio spectrum we showcase the complementarity of utilizing MD calculations to predict the PES evolution at high temperatures expected in our experiment. The comparison with the theoretical spectrum presented in the work of Manini et al., Phys. Rev. Lett. 91(19), 196402 (2003), furthermore, provides further evidence for a D5d symmetric ground state of the C60+ cation in the gas phase, in complement to IR spectroscopy in frozen noble gas matrices. This not only allows us to assign the first adiabatic ionization transition and thus determine the ionization energy of C60 with greater accuracy than has been achieved at 7.598 ± 0.005eV, but we also assign the two lowest excited states (2E1u and 2E2u) which are visible in our TPES. Finally, we discuss the energetics of additional DIBs that could be assigned to C60+ in the future.

Multireference Correlated Oscillator Strengths from Adiabatic Connection Approaches Based on Extended Random Phase Approximation.

We show that accurate oscillator strengths can be obtained from adiabatic connection (AC) approaches based on the extended random phase approximation (ERPA) combined with multireference (complete active space, CAS) wave functions. The oscillator strengths calculated using the perturbation-corrected ERPA transition density matrices, proposed in this work, and the excitation energies calculated with recently introduced AC correlation energy methods, AC0 and AC0D, compete with accuracy in the perturbational CASPT2 approach and require less computational effort. AC0 and AC0D methods scale more favorably with the number of active orbitals than multiconfigurational perturbation approaches like CASPT2 and NEVPT2 thanks to their dependence on reduced density matrices up to the order of 2. Importantly, the newly developed approach for computing correlated transition dipole moments does not entail any additional costs, as all intermediate quantities become available when AC0 energies are being computed. We also test the performance of the recently proposed AC method corrected for the negative-transition contributions to the correlation energy, AC0D, for triplet excitation energies. Similarly, as for the singlet excitations, the correction improves the performance of the AC0 method, particularly for the low-lying excited states.

Excited States in Single-Stranded and i-Motif DNA with Silver Ions.

We have studied the excited states and structural properties for the complexes of cytosine (dC)10 chains with silver ions (Ag+) in a wide range of the Ag+ to DNA ratio (r) and pH conditions using circular dichroism, steady-state absorption, and fluorescence spectroscopy along with the ultrafast fluorescence upconversion technique. We also calculated vertical electronic transition energies and determined the nature of the corresponding excited states in some models of the cytosine-Ag+ complexes. We show that (dC)10 chains in the presence of silver ions form a duplex stabilized by C-Ag+-C bonds. It is also shown that the i-motif structure formed by (dC)10 chains is destabilized in the presence of Ag+ ions. The excited-state properties in the studied complexes depend on the amount of binding ions and the binding sites, which is supported by the calculations. In particular, new low-lying excited states appear when the second Ag+ ion interacts with the O atom of cytosine in the C-Ag+-C pairs. A similar picture is observed in the case when one Ag+ ion interacts with one cytosine via the N7 atom.

Spectroscopy of End-On Copper(II) Superoxido Complexes: A Wave Function-Based Analysis.

Wave function methods are employed to analyze the ground and low-lying excited states of bipyramid trigonal copper(II) superoxido complexes, up to their characteristic ligand to metal charge transfer band. Several multireference methods have been combined to provide new insights into the interpretation of their experimental absorption spectra. We show that the intraligand transition on the dioxygen leads to a dark state. Among the results, we shall highlight the finding of doubly excited states in the region of the d-d transitions and the subtle interplay between Cu(I) and Cu(II) in the ground and excited states. Some of these findings could be obtained only with multireference methods.

Ab initio spectroscopic studies of AlF and AlCl molecules

In this work, we report the results from our spectroscopic study on AlF and AlCl molecules. We carry out detailed electronic structure calculations in both the molecules, including obtaining the potential energy surfaces of the [Formula: see text] ground electronic state and some of the low-lying excited electronic states belonging to [Formula: see text] and [Formula: see text] symmetries. This is followed by evaluating the spectroscopic constants and molecular properties such as electric dipole moments and electric quadrupole moments. Throughout, we employ the multi-reference configuration interaction method and work with high-quality quadruple zeta basis sets. Further, transition dipole moments between the ground electronic state and singlet excited states are also studied. The relevant vibrational parameters are computed by solving the vibrational Schrödinger equation. Subsequently, the vibrational energy spacings and transition dipole moments between the vibrational levels belonging to the same electronic states are used to evaluate the spontaneous and black-body radiation-induced transition rates, followed by computing the lifetimes. Finally, the energy differences between rotational levels belonging to different vibrational levels and within an electronic state as well as the Einstein coefficients are reported.

Stabilization of Charge-Transfer Excited States in Biological Systems: A Computational Focus on the Special Pair in Photosystem II Reaction Centers.

Charge-transfer (CT) excited states play an important role in many biological processes. However, many computational approaches often inadequately address the equilibration effects of nuclear and environmental degrees of freedom on these states. One prominent example of systems in which CT states are of utmost importance is reaction centers (RC) in photosystems. Here we use a multiscale approach combined with time-dependent density functional theory to explore the lowest CT excited state of the special pair PD1-PD2 in the Photosystem II-RC of a cyanobacterium. We find that the nonequilibrium CT excited state resides near the Soret band, making an exciton the lowest-energy excited state. However, accounting for nuclear and state-specific dielectric equilibration along the CT potential energy surface (PES), the CT state PD1--PD2+ stabilizes energetically below the excitonic state. This underscores the crucial role of state-specific solvation in mapping the PES of CT states, as demonstrated in a simplified dimer model.

Nonlinear optical response of 1H-indene-based donor-acceptor chromophores. Influence of the higher-lying states on the first hyperpolarizability

The hyperpolarizabilities often fall short of the fundamental quantum limits. However, in case of 5-(diphenylamino)thiophen-2-yl substituted 1H-indene based donor-π-acceptor (D-π-A) chromophores, in spite of the preponderance of twisted intramolecular charge transfer state, we find that the first hyperpolarizability is modulated (limited!) due to the possible interference of the higher-lying excited states of significant oscillator strength with the lower-lying excited state.

Electronic and optical properties of tetrapod quantum dots under applied electric and magnetic fields

In this work, the ground and low-lying excited states in GaAs tetrapod-shaped nanocrystals and in CdTe/CdS core/shell tetrapod-shaped nanocrystals are computed in the case of a finite confinement potential model using the finite element method and the effective mass approximation. For the single material tetrapod, electron energy levels are studied as a function of size parameters and the intensity of externally applied electric and magnetic fields, while for the core/shell tetrapod the electron and hole states are analyzed relative to size parameters of the core and shell thickness. The results show that the energies are strongly influenced by the tip-arm geometry, arm diameter, shell thickness and the intensity of the electric and magnetic fields.

The Excited-State Lifetime of Poly(NDI2OD-T2) Is Intrinsically Short.

Conjugated polymers composed of alternating electron donor and acceptor segments have come to dominate the materials being considered for organic photoelectrodes and solar cells, in large part because of their favorable near-infrared absorption. The prototypical electron-transporting push-pull polymer poly(NDI2OD-T2) (N2200) is one such material. While reasonably efficient organic solar cells can be fabricated with N2200 as the acceptor, it generally fails to contribute as much photocurrent from its absorption bands as the donor with which it is paired. Moreover, transient absorption studies have shown N2200 to have a consistently short excited-state lifetime (∼100 ps) that is dominated by a ground-state recovery. In this paper, we investigate whether these characteristics are intrinsic to the backbone structure of this polymer or if these are extrinsic effects from ubiquitous solution-phase and thin-film aggregates. We compare the solution-phase photophysics of N2200 with those of a pair of model compounds composed of alternating bithiophene (T2) donor and naphthalene diimide (NDI) acceptor units, NDI-T2-NDI and T2-NDI-T2, in a dilute solution. We find that the model compounds have even faster ground-state recovery dynamics (τ = 45, 27 ps) than the polymer (τ = 133 ps), despite remaining molecularly isolated in solution. In these molecules, as in the case of the N2200 polymer, the lowest excited state has a T2 to NDI charge-transfer (CT) character. Electronic-structure calculations indicate that the short lifetime of this state is due to fast nonradiative decay to the ground state (GS) promoted by strong CT-GS electronic coupling and strong electron-vibrational coupling with high-frequency (quantum) normal modes.

Role of the Center of Mass Correction in Magnetic Form Factors for 19O and 21Na Exotic Nuclei with Different Interactions

The transverse magnetic electron scattering form factors of 19O and 21Na exotic nuclei were studied in the plane wave Born approximation (PWBA). The shell model calculations with three sd-shell interactions, USDA, USDB, and Wildenthal, were carried out for the ground and low-lying excited states. The exact center of mass correction in the Born approximation picture through the translation-invariant shell model (TISM) was included to modify the transverse form factors. The measured magnetic dipole moments were well reproduced with the core polarization (CP) effect introduced through the effective g-factors. The occupancies percentage with respect to the valence nucleons was also calculated.

3,4-Dimethylenecyclobutene: A Building Block for Design of Macrocycles with Excited State Aromatic Low-Lying High-Spin States.

3,4-Dimethylenecyclobutene (DMCB) is an unusual isomer of benzene. Motivated by recent synthetic progress to substituted derivatives of this scaffold, we carried out a theoretical and computational analysis with a particular focus on the extent of (anti)aromatic character in the lowest excited states of different multiplicities. We found that the parent DMCB is non-aromatic in its singlet ground state (S0), lowest triplet state (T1), and lowest singlet excited state (S1), while it is aromatic in its lowest quintet state (Q1) as this state is represented by a triplet multiplicity cyclobutadiene (CBD) ring and two uncoupled same-spin methylene radicals. Interestingly, the Q1 state, despite having four unpaired electrons, is placed merely 4.8 eV above S0, and there is a corresponding singlet tetraradical 0.16 eV above. The DMCB is potentially a highly useful structural motif for the design of larger molecular entities with interesting optoelectronic properties. Here, we designed macrocycles composed of fused DMCB units, and according to our computations, two of these have low-lying nonet states (i. e., octaradical states) at energies merely 2.40 and 0.37 eV above their S0 states as a result of local Hückel- and Baird-aromatic character of individual 6π- and 4π-electron monocycles.

Photoaquation of cis-[Rh(dppz)(phen)Cl2]Cl complex prospective as potential light-activated anti-cancer agent

The photoactivated drug usage in anti-cancer therapy, the working mechanism of which doesn’t rely on the formation of reactive oxygen species, allows reducing damage to healthy tissue by controlling toxicity. For instance, light-activated Rh(III) complexes show nuclease activity after irradiation with UV and visible light. However, literature analysis shows a lack of descriptions of basic photochemical mechanisms. Here we report the study of cis-[Rh(dppz)(phen)Cl2]Cl (DPPZPHEN, dppz is dipyrido[3,2-a:2′,3′-c]phenazine, phen is 1,10-phenanthroline) photochemistry in water solutions using stationary photolysis, nanosecond laser flash photolysis and ultrafast pump–probe spectroscopy. After the irradiation with 308 nm light, DPPZPHEN undergoes aquation, which results in the substitution of one chloride ligand by a water molecule and leads to the formation of [Rh(dppz)(phen)(H2O)Cl]Cl2. UV–vis spectra of complex and capillary electrophoresis data were collected and discussed. Laser flash photolysis (355 nm) demonstrates intermediate absorption attributed to the lowest electronic excited state (triplet) of the initial complex. The study of primary photophysical processes showed a rather complicated behavior of transient absorption, which could be described by a set of four exponential functions. The early photophysical processes were described by the scheme including the formation of two excited states of different natures, namely a dppz-based IL state and an LMCT state.