Doubly-excited States Research Articles

Strong-Coupling Modification of Singlet-Fission Dynamical Pathways.

We investigate theoretically the influence of strong light-matter coupling on the initial steps of the phototriggered singlet-fission process. In particular we focus on intramolecular singlet fission in a TIPS-pentacene dimer derivative described by a vibronic Hamiltonian including the optically active singlet excited states, doubly excited and charge transfer states, as well as the final triplet-triplet pair state. Quantum dynamics simulations of up to four dimers in the cavity indicate that the modified resonance condition imposed by the cavity strongly quenches the passage through the intermediate charge transfer and double-excitation states, thus largely reducing the triplet-triplet yield in the bare system. Subsequently, we modify the system parameters and construct a model Hamiltonian where the optically active singlet excitation lies below the final triplet-triplet state such that the yield of the bare system becomes insignificant. In this case we find that using the upper polariton as the doorway state for photoexcitation can lead to a much enhanced yield. This pathway is operative provided that the system is sufficiently rigid to prevent vibronic losses from the upper polariton to the dark-states manifold.

Tautomeric enhancement of 2-(1H-pyrazol-5-yl)pyridine in photoinduced proton transfer by water-assisted molecules

Theoretical insight of excited state proton transfer (ESPT) in 2-(1H-pyrazol-5-yl)pyridine abbreviated as PPP interacting with water wires: PPP(H2O)n where n = 13 has been presented in both static and dynamics studies. Explicit water molecules placed around PPP have been simulated to elucidate the intermolecular hydrogen bonding interactions between them. Hydrogen bond strengthening in the excited state (S1) has been verified by shorter bond distances and redshift of IR vibrational spectra involving the proton transfer (PT) process. Furthermore, on-the-fly excited state dynamics simulations of all complexes have been performed to provide detailed information on the PT mechanism. The dynamic results show that one water molecule added to the neighboring PPP as an intermolecular hydrogen bonding bridge can promote double excited state intermolecular proton transfer up to 36% compared with its intrinsic intramolecular hydrogen bond of the PPP system. Meanwhile adding a second or third water molecule could decrease the probabilities of PT. Especially in PPP(H2O)3, a rearrangement of water molecules is observed that PT occurs via one water molecule. Hence, the models with explicit water molecules interacting with PPP as intermolecular hydrogen bonding bridge are a great representative role played by water molecules of the PT process at the molecular level.

Analysis of extreme ultraviolet radiation and hydrodynamics simulation at the core of laser-produced nickel plasmas

The non-uniformity and transient nature of laser-produced plasma are critical factors that affect the analysis of the extreme ultraviolet spectra of highly charged ions and the diagnosis of plasma states. This paper systematically investigates the characteristics of extreme ultraviolet radiation and the hydrodynamic evolution of laser-produced nickel plasmas from two perspectives: high-spatio-temporal-resolution extreme-ultraviolet spectroscopic measurement and radiation hydrodynamics simulation. The consistency between the four-band experimental spectra and their theoretically simulated spectra confirms the accuracy of the atomic structure parameters and plasma state parameters. We also analyze the significant contribution of the 3d-4f double-excited state radiation to the spectral profile and discuss the influence of the self-absorption caused by plasma opacity on the characteristics of extreme ultraviolet radiation. The findings are crucial for accurately understanding the characteristics of extreme ultraviolet radiation, the hydrodynamic evolution, and the application of medium- and high-Z laser-produced plasma as a pulsed short-wavelength light source.

A thermochromic salicylaldehyde Schiff bases derivative with AIE properties due to twisted structure

Great attention has been attracted to the salicylaldehyde Schiff base due to its thermochromic and photochromic characteristics in the solid state. However, the boundary between photochromic and thermochromic salicylaldehyde Schiff base structures is still unclear, and few studies have been conducted to investigate their thermochromic behavior and structures in depth and systematically. In the present work, we have synthesized a novel salicylaldehyde Schiff base derivative (2,2′-((1E,1′E)-((2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diyl)-bis(azaneylylidene))bis(methaneylylidene))diphenol, BTB) with twisted structure, which possesses both thermochromic and aggregation-induced emission (AIE) characteristics, and systematically investigated its thermochromic properties, enol-keto isomerization, AIE properties, aggregated state, and excited state intramolecular proton transfer (ESIPT) process. Interestingly, in our study, we found that the color of the BTB molecule changed gradually during the heating process, and it can be found that the thermochromism of BTB is produced by the reversible equilibrium shift of the enol form and the keto forms due to the temperature change by the color difference test, the in-situ IR spectra and the DSC curves. Finally, the pathway of BTB proton transfer was analyzed through quantum chemical calculations, and it was found that enol ketone isomerization is achieved through single excited state intramolecular proton transfer, rather than the expected double excited state intramolecular proton transfer.

Experimental measurement of state selective double electron capture in 1.4-20 keV/u Ar<sup>8+</sup> collision with He

Electron(s) capture in highly charged ions collision with atoms and molecules is a fundamental process related to the electron transition between bound states belongs to two atomic-centers. The X-ray emission following electron capture is important for X-ray astrophysical modeling, fusion plasma diagnosing, and ion irradiated biophysics. Over past decades, momentum-imaging cold-target recoil ion momentum spectroscopy is one of significantly developed techniques and has been widely applied to measure the quantum state-selective population in electron(s) capture processes. Based on the cold target recoil ion momentum spectroscopy mounted at the 150 kV highly charged ion platform in Fudan University, the state-selectivity of double electron capture in 1.4-20 keV/u Ar<sup>8+</sup> on He collision was measured, and the relative cross sections of the 3<i>l</i>3<i>l</i>’to 3<i>l</i>7<i>l</i>’ double excited states were obtained. It is found that with the increase of collision energy, more quantum state-selectivity channels are open in the double electron capture (DEC) of Ar<sup>8+</sup>-He collision. It is also found that the relative cross section of the quantum state population is strongly dependent on the collision energy of the projectile ion. This present measurement not only enriches the state-selective cross-section repository and collision dynamics for highly charged ion charge exchange processes, but also provides experimental benchmarks for the available theoretical calculations.

Properties of ground state and quench dynamics of one-dimensional contact repulsive single-spin flipped Fermi gases

Based on the exact solution method, the ground state and quench dynamics properties of one-dimensional single-spin flipped Fermi gas with repulsion interaction are studied. With the Bethe wave function, the single-body correlation function and two-body correlation function of the ground state and those between different eigen-states can be reduced into a summation of simple functions, thereby greatly reducing the computational difficulty. For the system in the ground state, the single-body correlation functions and two-body correlation functions as well as momentum distributions for spin-up particles are investigated in real space with different interaction strengths. As the interaction strength increases, the number of nodes in the single-body correlation function remains unchanged, while the amplitude of oscillation decreases. Meanwhile, the number of peaks in the two-body correlation function increases by one due to interaction, indicating that the spin-down particle behaves as a spin-up particle. The momentum distribution becomes more smooth around Fermi surface with the interaction strength increasing. The interaction quench dynamics is investigated. The system is prepared in the ground state of ideal Fermi gas, and then the interaction strength is quenched to a finite positive value. The system evolves under time-dependent Schrödinger equation. The overlap between the initial state and eigen-state of post-quench interaction strength is expressed in the form of continued multiplication. The square of the modulus of this overlap, which represents the occupation probability, is calculated. We find that the occupation probabilities of the ground state and doubly degenerated excited state always have the first and the second largest value for an arbitrary interaction strength, respectively, which means that the difference in eigenenergy between these two states gives the primary period of oscillation. For relatively large particle number (<inline-formula><tex-math id="M2">\begin{document}$ N\geqslant10$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231425_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231425_M2.png"/></alternatives></inline-formula>), the primary period always does not change under different interaction strengths.It is found that in the case of interaction quenching, the momentum distribution and the correlation function show periodic oscillations. When the interaction strength is adjusted to a relatively small value, the oscillation periodicity is well-defined and the oscillation amplitude is small. The system can be approximated by a two-level model. When the interaction strength increases to a very large value, the oscillation periodicity worsens and the amplitude increases, but a primary period remains unchanged. Although the overall deviation is far from the initial state, it is very close to the initial state at time <inline-formula><tex-math id="M3">\begin{document}$ t=mL^2/(2\pi\hbar)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231425_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231425_M3.png"/></alternatives></inline-formula>. This is because the difference between most energy eigenvalues is almost an integral multiple of energy unit <inline-formula><tex-math id="M4">\begin{document}$ 2\times\left(2\pi/L\right)^{2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231425_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231425_M4.png"/></alternatives></inline-formula>.

Auger Shake-Up Assisted Electron Recapture.

The presence of doubly excited states (DESs) above the core-hole ionization threshold nontrivially modulates the x-ray absorption because the participator Auger decay couples DESs to the underlying low-energy core-hole continuum. We show that coupling also affects the high-energy continuum populated by the spectator Auger decay of DESs. For the K-L_{23}^{2} Auger decay of the 1s^{-1}3p^{-1}4s^{2}^{1}P state in argon, the competing nonresonant path is assigned to the recapture of the 1s photoelectron caused by emission of the fast electron from the shake-up K-L_{23}^{2} decay of the 1s^{-1} ion.

Leveling the Mountain Range of Excited-State Benchmarking through Multistate Density Functional Theory.

The performance of multistate density functional theory (MSDFT) with nonorthogonal state interaction (NOSI) is assessed for 100 vertical excitation energies against the theoretical best estimates extracted to the full configuration interaction accuracy on the database developed by Loos et al. in 2018 (Loos2018). Two optimization techniques, namely, block-localized excitation and target state optimization, are examined along with two ways of estimating the transition density functional (TDF) for the correlation energy of the Hamiltonian matrix density functional. The results from the two optimization methods are similar. It was found that MSDFT-NOSI using the spin-multiplet degeneracy constraint for the TDF of spin-coupling interaction, along with the M06-2X functional, yields a root-mean-square error (RMSE) of 0.22 eV, which performs noticeably better than time-dependent density functional theory (DFT) at an RMSE of 0.43 eV using the same functional and basis set on the Loos2018 database. In comparison with wave function theory, NOSI has smaller errors than CIS(D∞), LR-CC2, and ADC(3) all of which have an RMSE of 0.28 eV, but somewhat greater than STEOM-CCSD (RMSE of 0.14 eV) and LR-CCSD (RMSE of 0.11 eV) wave function methods. In comparison with Kohn-Sham (KS) DFT calculations, the multistate DFT approach has little double counting of correlation. Importantly, there is no noticeable difference in the performance of MSDFT-NOSI on the valence, Rydberg, singlet, triplet, and double-excitation states. Although the use of another hybrid functional PBE0 leads to a greater RMSE of 0.36 eV, the deviation is systematic with a linear regression slope of 0.994 against the results with M06-2X. The present benchmark reveals that density functional approximations developed for KS-DFT for the ground state with a noninteracting reference may be adopted in MSDFT calculations in which the state interaction is key.

Facilitation of controllable excitation in Rydberg atomic ensembles

Strongly-interacting Rydberg atomic ensembles have shown intense collective excitation effects due to the inclusion of single Rydberg excitation shared by multiple atoms in the ensemble. In this paper we investigate a counter-intuitive Rydberg excitation facilitation with a strongly-interacting atomic ensemble in the strong probe-field regime, which is enabled by the role of a control atom nearby. Differing from the case of a single ensemble, we show that, the control atom's excitation adds to a second two-photon transition onto the doubly-excited Rydberg state, arising an excitation facilitation for the ensemble atoms. Our numerical studies depending on the method of quantum Monte Carlo wave function, exhibit the observation constraints of this excitation facilitation effect under practical experimental conditions. The results obtained can provide a flexible control for the excitation of Rydberg atomic ensembles and participate further uses in developing mesoscopic Rydberg gates for multiqubit quantum computation.

Can anions possess bound doubly-excited electronic states?

Anions play an important role in many fields of chemistry. Many molecules possess stable anions, but these anions often do not have stable electronic excited states and the anion loses its excess electron once excited. All the known stable valence excited states of anions are singly-excited states, i.e., valence doubly-excited states have not been reported. As excited states are relevant for numerous applications, and constitute basic properties, we searched for valence doubly-excited states which are stable, i.e., exhibit energies below that of the ground state of the respective neutral molecule. We concentrated on two promising prototype candidates, the anions of the smallest endocircular carbon ring Li@C12 and of the smallest endohedral fullerene Li@C20. By employing accurate state-of-the-art many-electron quantum chemistry methods, we investigated the low-lying excited states of these anions and found that they possess several low-lying stable singly-excited states and, in particular, a stable doubly-excited state each. It is noteworthy that the found doubly-excited state of Li@C12- possesses a cumulenic carbon ring in sharp contrast to the ground and singly-excited states. The findings shed light on how to design anions with stable valence singly- and doubly-excited states. Possible applications are mentioned.

Rydberg Wire Gates for Universal Quantum Computation

Rydberg atom arrays offer flexible geometries of strongly interacting neutral atoms, which are useful for many quantum applications such as quantum simulation and quantum computation. Here, we consider an all-optical gate-based quantum computing scheme for the Rydberg atom arrays, in which auxiliary atoms (wire atoms) are used as a mean of quantum-mechanical remote-couplings among data-qubit atoms, and optical individual-atom addressing of the data and wire atoms is used to construct universal quantum gates of the data atoms. The working principle of our gates is to use the wire atoms for coupling mediation only, while leaving them in noncoupling ground states before and after each gate operation, which allows the double-excited states of data qubits to be accessible by a sequence of π or π/2 pulses addressing the data and wire atoms. Optical pulse sequences are constructed for standard one-, two-, and multi-qubit gates, and the arbitrary two-qubit state preparation is considered for universal computation prospects. We further provide a detailed resource estimate for an experimental implementation of this scheme in a Rydberg quantum simulator.

Direct measurement of biexcitons in monolayer WS2

The optical properties of atomically thin transition metal dichalcogenides are dominated by Coulomb bound quasi-particles, such as excitons, trions, and biexcitons. Due to the number and density of possible states, attributing different spectral peaks to the specific origin can be difficult. In particular, there has been much conjecture around the presence, binding energy and/or nature of biexcitons in these materials. In this work, we remove any ambiguity in identifying and separating the optically excited biexciton in monolayer WS2 using two-quantum multidimensional coherent spectroscopy (2Q-MDCS), a technique that directly and selectively probes doubly-excited states, such as biexcitons. The energy difference between the unbound two-exciton state and the biexciton is the fundamental definition of biexciton binding energy and is measured to be 26 ± 2 meV. Furthermore, resolving the biexciton peaks in 2Q-MDCS allows us to identify that the biexciton observed here is composed of two bright excitons in opposite valleys.

Dipole transition‐matrix elements and oscillator strengths for the C4+doubly excited states with Coulomb and screened Coulomb (Debye–Hückel) potentials

AbstractThe dipole transition‐matrix elements (DTMEs) and oscillator strengths (OSs) for the doubly excited states (DESs) in heliumlike carbon are investigated using the correlated exponential wavefunctions (CEW). The interactions between the charged particles are taken care of by using both Coulomb and screened Coulomb (Debye–Hückel) potentials. The singly excited 1s3p1P state and doubly excited 2p2 1Destate are also calculated using CEW. The singly excited states of C4+in terms of Debye length (DL) are calculated using the Ritz variational principle. The DESs for different DLs are determined using the stabilization method. The DTMEs and OSs for the transitions between the 2p2 1Destate and the 1s2p1P, 1s3p1P, 2s2p+1Po, 2s3p−1Po, 2s3p+1Po, 2p3d1Postates, along with the 2p2 1Deresonance parameters are reported for various DLs. The benchmark data for DTMEs and OSs for the DESs in the C4+ion in pure Coulomb and screened Coulomb environments, obtained by employing highly CEW functions and utilizing the stabilization method, are reported for the first time.

Excited States from State-Specific Orbital-Optimized Pair Coupled Cluster.

The pair coupled cluster doubles (pCCD) method (where the excitation manifold is restricted to electron pairs) has a series of interesting features. Among others, it provides ground-state energies very close to what is obtained with doubly occupied configuration interaction (DOCI), but with a polynomial cost (compared with the exponential cost of the latter). Here, we address whether this similarity holds for excited states by exploring the symmetric dissociation of the linear H4 molecule. When ground-state Hartree–Fock (HF) orbitals are employed, pCCD and DOCI excited-state energies do not match, a feature that is assigned to the poor HF reference. In contrast, by optimizing the orbitals at the pCCD level (oo-pCCD) specifically for each excited state, the discrepancies between pCCD and DOCI decrease by 1 or 2 orders of magnitude. Therefore, the pCCD and DOCI methodologies still provide comparable energies for excited states, but only if suitable, state-specific orbitals are adopted. We also assessed whether a pCCD approach could be used to directly target doubly excited states, without having to resort to the equation-of-motion (EOM) formalism. In our Δoo-pCCD model, excitation energies are extracted from the energy difference between separate oo-pCCD calculations for the ground state and the targeted excited state. For a set comprising the doubly excited states of CH+, BH, nitroxyl, nitrosomethane, and formaldehyde, we found that Δoo-pCCD provides quite accurate excitation energies, with root-mean-square deviations (with respect to full configuration interaction results) lower than those of CC3 and comparable to those of EOM-CCSDT, two methods with a much higher computational cost.

Doubly excited states in hot and dense plasmas: Beryllium-like ions for [formula omitted

Effects of the hot and dense plasma on the doubly excited states (DES) of the four-electron beryllium-like ions (BLI) with Z varying from 4 to 10 have been investigated by applying the stabilization method. The Debye–Huckel model has been used to describe the effective potential in the plasma. The four-electron ions are treated as an effective three-body problem by means of the method of model potential. One, four and five DESs lying above the 1s2 2p threshold are found to exist in the ions having Z=4, Z=5 and Z=6−10 respectively. For the plasma-free case our results for the energy and width of the DESs are in agreement with the available results in the literature. A detailed study is made on the changes of energy and width of the DESs of the ions with varying plasma screening strength. Particular emphasis is given to explore the effects of the plasma on the whole sequence of ions.

Energy calculations of the (2P2 1D); (3D2 1G) and (4F2 1I) doubly excited states of helium isoelectronic sequence (z ≤ 20) via the modified atomic orbital theory

We report in this paper the total energies of the 2p2 1D, 3d2 1G, 4f2 1I doubly excited states of Helium isoelectronic sequence with nuclear charge Z ≤ 20. Calculations are performed using the Modified Atomic Orbital Theory (MAOT) [1;2] in the framework of a variational procedure. The purpose of this study required a mathematical development of the Hamiltonian applied to Slater-type wave function [3] combining with Hylleraas-type wave function [4]. The study leads to analytical expressions which are carried out under special MAXIMA computational program. This proposed MAOT variational procedure, leads to accurate results in good agreement as well as with available other theoretical results than experimental data. In the present work, a new correlated wave function is presented to express analytically the total energies for each 2p2 1D, 3d2 1G, 4f 2 1I Doubly Excited States (DES) in the He-like systems. The present accurate data may be a useful guideline for future experimental and theoretical studies in the (nl2 ) systems.

Double-excited states of charge transfer band and 4f-4f in single-phase K3Gd(VO4)2:Tb3+/Sm3+ phosphors with superior sensing sensitivity for potential luminescent thermometers

Temperature is one of the fundamental parameters for thermodynamics and its accurate detection is necessary. The novel strategy of luminescent materials based on the fluorescence intensity ratio technique has been promised for thermometers in more practical environments to overcome the drawbacks of conventional thermometers in recent. Herein, the novel single-phase K3Gd(VO4)2:Tb3+/Sm3+ phosphors were successfully prepared, and the 4G5/2 → 6H9/2 (Sm3+) and 5D4 → 7F5 (Tb3+) transitions could be promised for luminescent thermometers. Besides, under the double-excited states of charge transfer band (CTB, 317 nm) and 4f-4f (478 nm) excitations, the K3Gd(VO4)2:Tb3+/Sm3+ phosphors exhibited different concentration quenching mechanisms in energy transfer processes and also showed superior absolute sensing sensitivity (Sa) and relative sensing sensitivity (Sr). Especially, the maximum Sa and Sr values reached up to 0.568 K−1 and 11.24% K−1, respectively and the temperature resolution of the KGV:0.2Tb3+/0.01Sm3+ phosphor was higher than 0.004 K under the excitation wavelength of CTB (317 nm), indicating that the double-excited states in the single-phase KGV:Tb3+/Sm3+ phosphors with superior sensing sensitivity could be a novel candidate for potential optical thermometers.

Double photoionization of atomic oxygen: Feshbach resonances in the two-electron continuum

We describe a joint experimental and theoretical investigation on oxygen double photoionization—the emission of two electrons from atomic oxygen following single photon absorption. High-resolution experimental measurements were performed at the Advanced Light Source, revealing sharp resonance structure superimposed on the more familiar Wannier-like, nearly-linear background. These resonance features are attributed to ionization-plus-excitation Feshbach resonances embedded in the double ionization continuum, doubly-excited states that lie above the double-ionization threshold. Such features are absent in the double photoionization cross section of He, or other quasi-two-electron systems, for which the doubly-ionized atomic core remains inert. For a corresponding theoretical analysis, the R-matrix with pseudostates (RMPS) method was invoked by calculating final-state, two-electron resonances-plus-continua wavefunctions and corresponding single-photon absorption cross sections. Overall agreement is found in the direct, background double photoionization cross section. However, the RMPS method, using a small basis due to practical computational limitations, was unable to reproduce quantitatively the smooth background or the sharper resonance features observed in the measurements, showing instead large-scale oscillations about the experimental background, and characteristic pseudoresonance jitter, associated with an insufficient convergence of the pseudostate representation to the true two-electron infinite series of Feshbach resonances embedded in the two-electron continuum. The prominent resonance structure observed highlights the need to consider multiple excitation processes in atoms more complex than He or quasi-two-electron systems.

Classical analytical description of negative hydrogen ions

Studies of negative hydrogen ions (NHI), such as, H– and D–, are important from both practical and fundamental points of view. One of the reasons for their practical importance has to do with heating tokamak plasmas by external beams of NHI. Another practical use is the injection of NHI in high-power proton accelerator facilities to enhance their performance. In addition, NHI are also important for studies of opacities of the atmospheres of the Sun and of A-type stars. We present a classical analytical description of NHI in the situation where the underlying hydrogen (or deuterium) atom constitutes a rapid subsystem while the outer electron represents a slow subsystem. We focus on the case where the inner electron is in a circular state, so that the subsystem “nucleus plus inner electron” does not have the average electric dipole moment — in distinction to previous studies where the presence of the average dipole moment was the crucial requirement. By using the separation of rapid and slow subsystems, we show analytically that there is a classical bound state in such system and studied its parameters. In particular, we calculate analytically the primary frequency of the radiation of such system. This could be used for its experimental detection. The states that we found for the above systems could be considered as classical counterparts of the double-excited states of NHI previously studied in the literature in frames of quantum mechanics. The existence of classical counterparts of the double-excited states of NHI is a counterintuitive result.

An unsymmetrical thermally activated delayed fluorescence emitter enables orange-red electroluminescence with 31.7% external quantum efficiency.

The thermally activated delayed fluorescence (TADF) emitters based on donor-acceptor (D-A) configuration were continuously developed in the past few years, whereas an unsymmetrical TADF emitter with A-D-A' configuration has never been reported. Herein, an A-D-A' type TADF emitter of TRZ-SBA-NAI was firstly developed by simultaneously integrating 2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione and 2,4,6-triphenyl-1,3,5-triazine acceptors into a spirobiacridine donor core. Due to the coexistence of double charge-transfer excited states, TRZ-SBA-NAI displayed dual emission containing a dominant orange-red emission and an anti-Kasha's rule sky-blue emission shoulder in solution. As doped into the host matrix, TRZ-SBA-NAI only exhibited an orange-red emission, together with a high photoluminescence quantum yield of 87%. The linear molecular shape imparted TRZ-SBA-NAI with a high horizontal dipole ratio of 88%. As a result, the TRZ-SBA-NAI based devices achieved a record-high external quantum efficiency of 31.7% with an electroluminescence peak at 593 nm. This finding not only enriches the diversity in TADF molecular design, but also unlocks the huge potential of A-D-A' type TADF emitters for excellent device performance.