Multi-resonance Effect Research Articles

Indolocarbazole Derivatives for Highly Efficient Organic Light‐Emitting Diodes

AbstractSince the discovery of the organic light‐emitting diode (OLED), scientists worldwide have dedicated extensive efforts to enhance the efficiency and reliability of devices, striving for superior performance. Various molecular structures have undergone structural modifications to assess their suitability in achieving the desired outcomes. This review focuses on indolo[3,2,1‐jk]carbazole (ICz), a building block that has garnered considerable attention within the OLED community. The rigid and fused ICz core induces a multiresonance effect through an alternating distribution of frontier molecular orbitals. Notably, ICz‐based thermally activated delayed fluorescence emitters exhibit a full width at half maximum below 20 nm, ensuring high color purity, and boast an external quantum efficiency above 30%, comparable to state‐of‐the‐art narrow‐emitting boron–nitrogen‐type materials. Furthermore, the ICz core is a building block in host and metal complexes, enhancing stability, efficiency, and color purity. Consequently, the ICz core is promising as a central component in host and emitters, improving OLED device performance. This review aims to succinctly summarize studies on ICz‐based organic materials within the OLED field, offering insights into future perspectives regarding developing and applying ICz‐derived organic compounds.

Broadband, thin thickness and low filling ratio microwave absorption by constructing Sm2Fe17/Fe(Sm) hard/soft magnetic nanoparticles in Sm2O3-doped porous carbon matrix

Exchange-coupled hard/soft magnetic composites are supposed to be promising microwave absorber, due to the multiple-resonance peaks in permeability. However, due to insufficient magnetization and dielectric loss, soft/hard ferrite magnets are difficult to achieve further breakthroughs in microwave absorption performance. In this work, the special hard/soft magnetic composites are successfully fabricated, in which Sm2Fe17/Fe(Sm) hard/soft hybrid nanoparticles are embedded in ∼5 nm Sm2O3-doped porous carbon matrix. The hard/soft magnetic exchange-coupling result in the multiple-resonance peaks beyond Snoek’s limitation at broad wave band and the Sm2O3-doped carbon supplements dielectric loss capacity. Multiple-resonance effect is modified by adjusting the ratio of hard and soft magnetic components and the dielectric loss capacity is supplemented by Sm2O3-doped carbon. Herein, the hard/soft magnetic exchange-coupling and dielectric matrix are dexterously integrated to achieve broad absorption band with thin matching thickness and low filling ratio. By varying the ratio of Fe3+/Sm3+ in raw material, 20 wt% Sm2Fe17/Fe(Sm)-paraffin composites can reach the maximum effective absorption bandwidth of 6.8 GHz with matching thickness of 1.6 mm, the minimal reflection loss of −47.15 dB with 1.5 mm and the optimal microwave absorption efficiency of 71.1 dB·GHz/mm with 1.4 mm. Overall, this work provides a simple approach to introduce multi-resonance effect, which broadens the path for advanced absorbers with broad band and thin thickness and low filling ratio.

Modulating excited state properties of thermally activated delayed fluorescence molecules by hybrid long-range and short-range charge transfer strategy

Balancing the rapid radiative decay process and the fast reverse intersystem crossing (RISC) process of thermally activated delayed fluorescence (TADF) molecule remains a great challenge and efficient molecular design strategies are highly desired. Herein, from a theoretical perspective, excited state properties of three reported TADF molecules (1TICz, 1BOICz and 2BOICz) are investigated based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations coupled with the thermal vibration correlation function (TVCF) method. Results indicate that, by introducing the multi-resonance (MR) acceptor, 1BOICz possesses hybrid long-range and short-range charge transfer features, balanced small energy gap (ΔEST) and large oscillator strength (f) is obtained. Furthermore, by incorporating double equivalent MR acceptors in 2BOICz, largely enhanced f with slightly changed ΔEST is achieved, inner mechanism for remarkable photophysical property is illustrated. Keep this strategy, seven new TADF molecules (2pDBA-bICz-1, 2pDBA-bICz-2, 2OSBA-bICz, 2DQAO-bICz, 2QAO-bICz, 2SQAO-bICz and 2OQAO-bICz) are theoretically designed, detailed physical parameters are analyzed and excited state energy consumption process is studied. Strong electrophilicity on acceptor is determined and the strength of nucleophilic sites on the bridge-phenyl of 2DQAO-bICz, 2QAO-bICz, 2SQAO-bICz and 2OQAO-bICz is increased, this promotes the short-range charge transfer property. In addition, the excitation processes for all studied molecules are dominated by long-range charge transfer from donor to acceptors, and supplemented by the short-range charge transfer on the bridge-phenyl with MR effect. Compromise energy gap and oscillator strength as well as large spin orbit coupling (SOC) constant are obtained for designed molecules. Thus, by regulating the long-range and short-range charge transfer ratios, excited state properties are successfully modulated and new efficient TADF molecules are proposed. Our research aims to provide deeper insight into long-range and short-range charge transfer features in balancing small ΔEST and large f, which could facilitate the development of novel efficient TADF molecules.

Naphthalene Embedded Multi-Resonance Emitters Enabling Efficient Narrow Emissive Blue OLEDs.

Achieving high color purity for blue emitters remains a challenge in organic light emitting diodes. In this study, we have designed and synthesized three naphthalene (NA) embedded multi-resonance (MR) emitters, named SNA, SNB and SNB1, based on N-B-O frameworks with isomer variations for finely adjusting the photophysical properties. These emitters show tunable blue emission with emission peaks of 450-470 nm. Small full width of half maximumof 25-29 nm are achieved in these emitters, indicating the well maintaining of molecular rigidity and MR effect with NA extension. Such design also ensures a fast radiative decay. No obvious delayed fluorescence is observed in all three emitters due to the relatively large energy differences between the first singlet and triplet excited states. Both SNA and SNB enable high electroluminescent (EL) performance in doped devices with external quantum efficiency (EQE) of 7.2% and 7.9%, respectively. When applying the sensitized strategy, devices based on SNA and SNB show huge improvement with EQE of 29.3% and 29.1%. More importantly, SNB with twist geometry enables stable EL spectra with almost unchanged FWHM under different doping concentrations. This work demonstrates the potential of NA extension design in constructing narrowband emissive blue emitters.

Helically Chiral Donor–Acceptor Double Hetero[4]helicenes with Circularly Polarized Thermally Activated Delayed Fluorescence

AbstractAlthough helically chiral heterohelicenes are widely adopted in chiroptical studies, those with circularly polarized thermally activated delayed fluorescence (CP‐TADF), which are highly valuable for circularly polarized organic light‐emitting diodes (CP‐OLEDs), are rarely realized. Moreover, the core skeletons of known CP‐TADF heterohelicenes are limited to the p‐ and n‐doped structures with multiresonance effect. In this study, a new type of helically chiral CP‐TADF heterohelicenes featuring a fused donor–acceptor core skeleton is successfully designed and constructed. Enantiomers possessing high configurational stability are achieved and separated, and they efficiently emit CP light with dissymmetry factors reaching 3.1 × 10−3 in doped films. Owing to the excellent photophysical properties, a high‐performance CP‐OLED with the maximum external quantum efficiency of up to 20.0% and an electroluminescence dissymmetry factor reaching 2.9 × 10−3 is obtained. This new type of CP‐TADF heterohelicenes provides a large space for the development of high‐performance CP‐TADF materials for various applications.

Selenium-Doped Polycyclic Aromatic Hydrocarbon Multiresonance Emitters with Fast Reverse Intersystem Crossing for Narrowband Blue Emission.

Two kinds of boron- (B), selenium- (Se), and nitrogen-doped (N) polycyclic aromatic hydrocarbon (PAH) emitters (Cz-BSeN and DCz-BSeN) with a multiresonance effect are developed for narrowband blue emission by embedding boron as an electron-deficient atom and selenium and nitrogen as electron-donating atoms into a benzo[a]naphtho[1,2,3-hi]aceanthrylene skeleton. It is found that both emitters exhibit strong spin-orbit coupling and fast reverse intersystem crossing (rate constant of 7.5-8.8 × 106 s-1) due to the heavy-atom effect of selenium, which is 2 orders of magnitude faster than its B, N-doped PAH analogue. Meanwhile, compared to parent B, Se, N-doped PAH emitter Cz-BSeN, incorporating carbazole moieties on the para position of the boron atom in DCz-BSeN not only blueshifts the emission by 7 nm without broadening its spectra but also results in an enhanced photoluminescent quantum efficiency of 93% in the doped film. The organic light-emitting diode (OLED) employing DCz-BSeN as emitter revealed narrowband blue emission at 481 nm with a small full-width at half-maximum (fwhm) of 32 nm, as well as a maximum external quantum efficiency of 22.3%, accompanied by alleviated efficiency roll-off compared to its B, N-containing counterpart.

Multiple resonance type thermally activated delayed fluorescence by dibenzo [1,4] azaborine derivatives.

We studied the photophysical and electroluminescent (EL) characteristics of a series of azaborine derivatives having a pair of boron and nitrogen aimed at the multi-resonance (MR) effect. The computational study with the STEOM-DLPNO-CCSD method clarified that the combination of a BN ring-fusion and a terminal carbazole enhanced the MR effect and spin-orbit coupling matrix element (SOCME), simultaneously. Also, we clarified that the second triplet excited state (T2) plays an important role in efficient MR-based thermally activated delayed fluorescence (TADF). Furthermore, we obtained a blue–violet OLED with an external EL quantum efficiency (EQE) of 9.1%, implying the presence of a pronounced nonradiative decay path from the lowest triplet excited state (T1).

Highly efficient and stable deep-blue OLEDs based on narrowband emitters featuring an orthogonal spiro-configured indolo[3,2,1-de]acridine structure.

High-efficiency and stable deep-blue bottom-emitting organic light-emitting diodes with Commission Internationale de l'Eclairage y coordinates (CIEys) < 0.08 remain exclusive in the literature owing to the high excited-state energy of the emitters. Here, we propose the utilization of narrowband emitters to lower the excited-state energy for stable deep-blue devices by taking advantage of their high color purity. Two proof-of-concept deep-blue emitters with nitrogen-containing spiro-configured polycyclic frameworks are thereafter developed to introduce a multi-resonance effect for narrow emissions and sterically orthogonal configurations for alleviated molecular interactions. Both emitters show bright ultrapure deep-blue emissions with an extremely small full-width-at-half-maxima of only 18–19 nm, which can be maintained even in heavily doped films. Small CIEys of 0.054 and 0.066 are therefore measured from the corresponding electroluminescence devices with peak energies of only 2.77 eV (448 nm) and 2.74 eV (453 nm), accounting for the remarkably long LT80s (lifetime to 80% of the initial luminance) of 18 900 and 43 470 hours at 100 cd m−2, respectively. Furthermore, by adopting a thermally activated delayed fluorescence sensitizer, impressive maximum external quantum efficiencies of 25% and 31% are recorded respectively, representing state-of-the-art performances for deep-blue devices.

Solution-Processed Pure Blue Thermally Activated Delayed Fluorescence Emitter Organic Light-Emitting Diodes With Narrowband Emission.

There is a need to satisfy the high color purity requirement of display technology with a simply fabricated process. Herein, solution-processed blue thermally activated delayed fluorescence organic light-emitting diodes (OLEDs) with a narrow spectrum with a full width at half maximum (FWHM) of 32 nm and y color coordinate below 0.2 are demonstrated by employing a molecule containing boron and nitrogen atoms (TBN-TPA) as the guest emitter in the emissive layer. The opposite resonance positions of B-N atoms of TBN-TPA endows a multi-resonance effect, leading to high color purity.

Multi-resonance interaction in rectangular waveguide grating structure

For developing millimeter and sub-millimeter wave devices, the rectangular waveguide grating sheet beam system is a very promising way to realize a high power operation. To further improve the interaction efficiency, we can substitute the cyclotron beam for the rectilinear one and utilize the multi-resonance effect. In rectangular coordinates, we rigorously derive the formulae to describe the Lorentz forces acting on the electrons and the coupling coefficients of each concerned resonance. The theoretical calculation demonstrates that the combined gain is evidently enhanced when the multi-resonance condition is satisfied, the occurrence of which is always caused by the coupling of two major resonances. The results also show that the multi-resonance effect will rapidly disappear if the beam voltage and the magnetic field deviate from their exact values. Although the parameters should be carefully sustained, the multi-resonance can be excited by using the fundamental TEx10 hybrid mode, which is beneficial for the stable operation. So, as an available mechanism to upgrade the future device performance, it is worth being particularly studied.

Laboratory investigation on the role of tubular shaped micro resonators phononic crystal insertion on the absorption coefficient of profiled sound absorber

This paper emphasizes the influence of tubular shaped microresonators phononic crystal insertion on the sound absorption coefficient of profiled sound absorber. A simple cubic and two different bodies centered cubic phononic crystal lattice model were analyzed in a laboratory test procedure. The experiment was conducted by using transfer function based two microphone impedance tube method refer to ASTM E-1050-98. The results show that sound absorption coefficient increase significantly at the mid and high-frequency band (600 - 700 Hz) and (1 - 1.6 kHz) when tubular shaped microresonator phononic crystal inserted into the tested sound absorber element. The increment phenomena related to multi-resonance effect that occurs when sound waves propagate through the phononic crystal lattice model that produce multiple reflections and scattering in mid and high-frequency band which increases the sound absorption coefficient accordingly

Bandwidth enhancement of a CPW-fed monopole antenna with small fractal elements

In this paper, a technique of adding small fractal elements to the polygon shape radiator of a CPW-fed monopole antenna for bandwidth enhancement is proposed and experimentally studied. Based on the multi-resonance effect of the fractal elements, three closely spaced resonant frequencies are produced over the antenna bandwidth which leads to coverage of the standard UWB bandwidth (3.1–10.6GHz). Effects of increasing the number of the polygon sides on S11 and radiation patterns are also investigated. Finally, three prototypes of the proposed antenna are fabricated and measured in order to verify the simulation results.

Size reduction and multi-resonance effects of slotted single-layer edge-fed patch antennas

In this work, easy to fabricate edge-fed, single-substrate, slotted, square-patch antennas were designed, fabricated, and measured. Effects of slots on patch antenna, such as the size reduction effect and the multi-resonance effect, are demonstrated by examples. Measurements show that up to four additional resonant frequencies below the original patch antenna’s TM020 frequency are obtainable and that the size of the antenna can be reduced to less than approximately 40% its original size. The size reduction property of the proposed antenna may be suitable for miniaturized planar and conformal antennas that are needed for personal communication devices, and the multifrequency property of the proposed antenna has the advantage of serving multiple frequencies with one antenna.

Modelling of edge localized modes with a current relaxation model on JET and TEXTOR

The mitigation of edge localized modes (ELMs) has been investigated using external resonant magnetic perturbations (RMPs) on JET. An interesting observation encountered is the formation of resonant structures in the dependence of ELM frequency on the edge safety factor. Using a theory based on an extended Taylor relaxation process, initialized by an external peeling mode, this behaviour is modelled and analysed leading to a prediction of a condition that a low edge current density is required for the resonant nature to be observed. This model is outlined and the results compared with recent experimental observations from JET.The TEXTOR tokamak already has a low edge current density due to its limiter configuration and so is predicted to show the resonant behaviour even without the RMP fields being applied. Similar experiments investigating the effect of the edge safety factor on the ELM frequency are conducted on TEXTOR to validate this prediction. It was found from the model that a case with a low normalized edge current density of 0.01 shows good agreement with observations. For such a case the multi-resonance effect is less well defined than observed on JET due to the appearance of highly detailed structure in the model predictions.

Observations of multi-resonance effect in ELM control with magnetic perturbation fields on the JET tokamak

Multiple resonances of the edge-localized mode (ELM) frequency caused by the application of low n (=1 or 2) magnetic perturbations for ELM control have been observed on JET. With a low n field applied, a strong increase in ELM frequency, fELM, by a factor of ∼4.5 was found in many separated narrow windows of q95 (resonant q95), while the fELM increased only by a factor of ∼2 for non-resonant q95 values. The fractions of increase in fELM with different resonant q95 values are not the same. An analysis of ideal external peeling modes shows that both the dominant unstable peeling mode number and fELM depend on the amplitude of the normalized edge current density as well as the edge safety factor, qa.

A Localized Enhanced Power Plane Topology for Wideband Suppression of Simultaneous Switching Noise

Using a complementary spiral resonator mounted on the power plane, simultaneous switching noise and ground bouncing noise can be suppressed over a very wideband from 0.22 to 12.5 GHz under a noise suppression margin of -25 dB. Not only the suppression characteristic under 12.5 GHz is possible, but also over the higher frequency band, because the proposed structure operates like an RF choke. Therefore, the proposed structure can satisfy the 10% noise margin for the voltage swing ratio for both periodic and random clock signals. A size of 3.2 mm is necessary for the diameter of the resonator on the power plane, and is comparable to a clearance pad size with diameter of 3.0 mm in a ground plane. Hence, the small size helps to reduce the discontinuity of the return current path; therefore, signal integrity problems and the degrees of freedom for power plane design of an electromagnetic bandgap structure are enhanced. Moreover, the effects of inductance and capacitance in the spiral resonator are analyzed for modeling. As a result, the suppression bandwidth and resonance frequency are controlled by the arm length and gap of spiral resonator. In addition, by applying two different sizes of resonators, it is shown that a multiresonance effect is also obtained.