Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials have emerged as promising emitters for high-performance organic light-emitting diodes (OLEDs) due to their narrowband emission and high exciton utilization efficiency. However, the trade-off between efficient reverse intersystem crossing (RISC) and high color purity remains a key challenge, explorations of the internal physical mechanism are highly desired. In this work, systematic theoretical investigations are carried out on a series of MR-TADF molecules, including three experimentally reported compounds (TSBA, TSBA-Cz, TSBA-PhCz) and six newly designed derivatives (TSBA1, TSBA2, TSBA3, CzBO-Cz, CzBS-Cz, and CzBSe-Cz). Basic geometric and electronic properties for ground and excited states are studied by density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively. Related energy gaps are corrected by SCS-ADC(2) method and excited state decay processes are investigated by thermal vibration correlation function (TVCF) method. The results reveal that molecular substitution significantly modulates the frontier molecular orbital distribution, excited-state character, and singlet-triplet energy gap (ΔEST). Hybrid local and charge-transfer (HLCT) characteristics are determined and this is beneficial for balancing oscillator strength and a small ΔEST. In contrast, molecules with strong charge-transfer (CT) character show extremely small ΔEST and fast RISC rates but suffer from severely reduced radiative decay and enhanced non-radiative decay rates. Furthermore, structural rigidity and excited-state geometric relaxation play a crucial role in determining emission bandwidth. Molecules with high planarity and small structural reorganization exhibit weaker vibronic coupling and narrower emission spectra. Analysis indicates that TSBA-PhCz, TSBA1, CzBS-Cz, and CzBSe-Cz achieve an optimal balance among radiative decay (kr), intersystem crossing (kISC), and reverse intersystem crossing (kRISC), demonstrating superior photophysical performance. In contrast, TSBA2 and TSBA3, despite their ultrafast RISC process, show poor emission efficiency due to dominant CT character. This work reveals the quantitative relationship between structure and performance and provides specific design guidelines for photophysical processes in MR-TADF systems, offering valuable design guidelines for developing high-efficiency and high color purity OLED emitters.

Orange-red thermally activated delayed fluorescence (TADF) molecules show great potential for OLEDs. Based on density functional theory (DFT) and the thermal vibration correlation function (TVCF) method, the luminescence mechanisms of the bridged open-ring structure T-DMAC-PPyM and the bridged closed-ring structure P-DMAC-BPyM are investigated in both toluene and the solid state. The fluorescence efficiency (Phi F) of the T-DMAC-PPyM in toluene is slightly higher than that of P-DMAC-BPyM, which is due to the larger radiation rate (kr) and smaller non-radiative decay rate (knr). In contrast, the sharply increased kr of P-DMAC-BPyM in the solid state leads to a much higher Phi F than that of T-DMAC-PPyM. In addition, P-DMAC-BPyM reduces LEST in the solid state and increases the spin-orbit coupling (SOC) constant, which is beneficial to improve the reverse intersystem crossing rate (RISC). Studies have shown that T-DMAC-PPyM has better intrinsic fluorescence properties, while P-DMAC-BPyM has better TADF properties in the solid state.

Thermally activated delayed fluorescence (TADF) emitters have been extensively investigated theoretically for their light-emitting properties in organic light-emitting diodes (OLEDs). However, the influence of an external electric field (EEF), an inherent factor in operating OLEDs, on the luminescence behavior of TADF materials has rarely been addressed. In this study, we selected two representative TADF systems, a donor-acceptor (D-A) type and a multiple-resonance type (MR-TADF), to systematically evaluate the effect of EEF on their emission characteristics across gas, solution, and solid phases. Our findings reveal that the MR-TADF emitter exhibits greater sensitivity to EEF than its D-A counterpart. Moreover, when the EEF is aligned with the molecular dipole moment direction, it exerts a more pronounced modulation on both absorption and emission properties. These results provide valuable and comprehensive insights into the optoelectronic behavior of TADF emitters under device-relevant conditions.

A thorough understanding of the conversion process of triplet excitons is crucial for achieving controllable thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) in donor-acceptor (D-A) emitters. Here, we combine a multiscale calculation method and thermal vibration correlation function theory to elucidate the excited-state dynamics of five saccharin-based D-A emitters (6-Cz-Sac, 5-Cz-Sac, DiCz-Sac, 5-Sac-Pxz, and 5-Sac-Ptz) and construct a unified mechanistic picture. In tetrahydrofuran solution, all emitters exhibit weak S1 radiative decay accompanied by fast nonradiative loss, which intrinsically limits emission efficiency. 6-Cz-Sac and 5-Cz-Sac show inefficient triplet recycling due to the slow RISC process relative to the ISC process, resulting in dominant nonradiative loss from the T1 state. In contrast, DiCz-Sac enables efficient triplet recycling through a compact triplet-state energy level with a dominant T2-assisted RISC channel, while 5-Sac-Pxz and 5-Sac-Ptz operate via a conventional single-channel TADF mechanism driven by the very small S1-T1 gaps. In the solid state, crystal packing suppresses structural relaxation and extends the triplet state lifetimes. Hydrogen-bond short contacts around the saccharin acceptor further provide effective intermolecular locking and reduce nonradiative loss, thereby activating triplet branching as the decisive factor governing the emission. As a result, 6-Cz-Sac and 5-Cz-Sac become RTP-dominated, DiCz-Sac exhibits concurrent TADF and RTP due to competition between T2-assisted up-conversion and phosphorescence, and 5-Sac-Pxz/5-Sac-Ptz maintains single-channel TADF emission. Overall, this work reveals how donor engineering and solid-state confinement together determine triplet fate, enabling selective access to RTP, mixed TADF/RTP, or conventional TADF within a unified saccharin-based platform.

The ability to test the limits of diodes scaled down to the molecular (quantum) scale could advance the development of nanoelectronic devices. So far, strategies for molecular rectification have mostly relied on the intrinsic asymmetry of molecules or on changes in the external environment. These approaches require complex synthetic designs or specific device structures, and their performance is far beyond theoretical prediction. Here, we report an alternative strategy that leads to giant rectification by inducing a topological change in the molecular conformation through unidirectional electric-field-driven electron delocalization, an approach also applicable to molecules without asymmetric structures. This method reverses the polarity of the applied bias, which induces the rectifying group to oxidize and transition from a buckled and cross-conjugated group into a planar aromatic group. As a result, the transformed molecule forms a fully conjugated structure resulting in a substantial increase in the current density.

Smaller ionization energy and electronegativity enable the emission range of Eco-friendliness Sn-based perovskite light-emitting diodes (PeLEDs) researched to near-infrared range, which exhibits a wide range of applications in night vision, biomedicine, and communications. Nevertheless, the oxidizability of Sn2+ and the rapid crystallization rate of Sn-based perovskites lead to poor film quality, thus leading to diminished efficiency in tinbased PeLEDs. We developed effective Near-infrared (NIR) PeLEDs based on FA0.875Cs0.125SnI3 by using D-serine benzyl ester hydrochloride (D-SBEHC) as an additive, which has significant steric hindrance and multifunctional groups. The hydrogen bonding and coordination between D-SBEHC and FA0.875Cs0.125SnI3 effectively diminish the crystallization rate of the perovskite, inhibit the oxidation of Sn2+, and prevent the production of defects. The perovskite films modified by D-SBEHC exhibit nearly threefold increase inphotoluminescence quantum yield. Finally, we fabricated an efficient and stable PeLED with a peak at 903 nm, showing an external quantum efficiency (EQE) of 3.99% (eight times that of the control device) and a maximum radiance of 31 W/sr/m2.

Deep-red perovskite lasers hold great promise for biomedical and optoelectronic applications, yet their performance is hindered by Auger recombination at high carrier densities. This study demonstrates that molecular dipole-moment engineering effectively suppresses Auger recombination in CsPb(I x Br1-x )3 perovskite films. By introducing a passivation molecule with a strong electron-withdrawing group and a large dipole moment, the surface electron cloud is redistributed. This not only passivates defects but also reduces the exciton binding energy and enhances lattice rigidity, thereby weakening both defect-assisted and Auger recombination. Transient absorption spectroscopy confirms an extended Auger lifetime and improved optical gain. As a result, the optimized film achieves low-threshold amplified spontaneous emission at 3.4 mu J cm-2 in the deep-red region. This work highlights dipole-moment manipulation as a potent strategy for developing high-performance, low-threshold perovskite lasers.

Constructing two-dimensional van der Waals magnetic tunnel junctions with the giant tunneling magnetoresistance effect is crucial towards miniaturized spintronic devices. Herein, we introduce a two-dimensional van der Waals magnetic tunnel junction based on the VSi2N4 half-metal and the Janus MoSiGeN4 semiconductor material, and comprehensively investigate the spintronic transport properties by using density functional theory combined with the non-equilibrium Green's function method. A spin filtering efficiency close to 100% is achieved for the VSi2N4/MoSiGeN4/VSi2N4 magnetic tunnel junction with a parallel magnetic configuration, and, surprisingly, a large tunnel magnetoresistance ratio is obtained. Due to the intrinsic dipole moment of Janus MoSiGeN4, a large tunnel dipole-induced resistance ratio of 6999% is observed in the VSi2N4/bilayer-MoSiGeN4/VSi2N4 van der Waals magnetic tunnel junction at zero bias voltage, and it can be further improved by tuning the bias voltage. Importantly, the high spin filtering efficiency and the large tunneling magnetoresistance ratios are maintained throughout the entire bias voltage range. The large tunneling magnetoresistance effect is attributed to the absence of electron states in both spin-conducting channels near the Fermi level in the antiparallel magnetic configuration. Subsequently, we classify the six distinct magnetic and electric combinations of the magnetic tunnel junctions into four distinguishable storage states. Multilevel data storage is thereby achieved through the cooperative control of magnetic and electrical switching. We demonstrate that the VSi2N4/MoSiGeN4/VSi2N4 and VSi2N4/bilayer-MoSiGeN4/VSi2N4 van der Waals magnetic tunnel junctions are promising candidates for next-generation spintronic devices.

Violet-light emitters serve critical functions across diverse domains, spanning biology, photopolymerization processes, and anti-counterfeiting solutions. In perovskite materials, the partial substitution of Pb2+ with Sr2+ at the B-site enables the preparation of perovskite films with continuously tunable emission from green to violet. These films exhibit excellent photoluminescence quantum yields, highlighting the potential of Sr-based metal halide perovskites for violet-emitting applications. However, excessive introduction of Sr2+ increases the carrier effective mass, resulting in a significant decline in carrier mobility. Herein, we demonstrate that K+ doping optimizes the carrier effective mass, which contributes to a notable enhancement in carrier mobility. Density functional theory (DFT) calculations indicate that the carrier mobility in K+-modified perovskite is approximately 1.5 times that of the pristine perovskite. Moreover, the disparity between electron and hole mobilities is reduced, indicating a more balanced trend in charge transport properties. The K+-modified device exhibited a stable emission peak at 420 nm and achieved a maximum external quantum efficiency (EQE) of 0.35%, representing high performance among violet perovskite light-emitting diode (PeLEDs). This work presents a facile strategy for fabricating high-performance violet PeLEDs with enhanced efficiency and stability.

Four-coordinate boron acceptors have recently emerged as highly effective building blocks for thermally activated delayed fluorescence (TADF) emitters, yet their intrinsic structure-property relationships at the molecular level remain insufficiently understood. In this work, a systematic theoretical investigation is performed on three pyrimidine-based emitters, PM-SPAc, PM-B-SPAc, and Spiro-PM-B-SPAc, to elucidate the role of boron-nitrogen (B-N) coordination and intramolecular locking in regulating the excited state properties. The introduction of four-coordinate boron significantly reduce the lowest unoccupied molecular orbitals (LUMO), leading to a reduction of ΔEST from 0.30 eV (PM-SPAc) to 0.01 eV (Spiro-PM-B-SPAc-oniom). Natural transition orbitals (NTOs) analysis confirms pronounced charge transfer (CT) character with minimized overlap between the highest occupied NTO (HONTO) and the lowest unoccupied NTO (LUNTO), while spin-orbit coupling (SOC) matrix elements are enhanced upon boron coordination. Importantly, the calculated reverse intersystem crossing rate (kRISC) increases dramatically, reaching 5.99×106 s-1 in the B-N coordinated system with the locking strategy in the solid phase, due to near-degenerate S1 and T1 and suppressed structural reorganization. Although internal conversion remains competitive, the synergistic effects of reduced ΔEST, improved SOC, and conformational rigidity enable highly efficient triplet harvesting. These results provide comprehensive theoretical insight into how B-N coordination combined with structural locking modulates the excited state dynamics and establish clear molecular design principles for next-generation high-efficiency TADF emitters for organic light-emitting diodes (OLEDs) applications.

Strain engineering offers a powerful route to tailor the chemical reactivity and electronic response of two-dimensional GeSe, yet its impact on gas-sensing selectivity remains insufficiently understood. Here, we combine density functional theory and the nonequilibrium Green's function (NEGF) method to reveal a strain-governed sensing mechanism in monolayer GeSe toward nitrogen-containing pollutants (NO, NO2, and NH3). Pristine GeSe exhibits intrinsic selectivity for NO2, where adsorption triggers a semiconductor-to-metal transition, whereas interactions with NO and NH3 are comparatively weak. Remarkably, a modest 4% biaxial compressive strain transforms GeSe into a fully discriminative sensing platform: NO2 adsorption produces a pronounced conductivity increase via metallic switching, NO yields strongly spin-polarized currents approaching a 100% filtering efficiency, and NH3 induces only minimal electronic perturbation. These distinct response signatures arise from strain-enhanced gas adsorption, bandgap renormalization, and reconfigured transport pathways. Recovery-time analysis further reveals rapid desorption, confirming the practical recyclability. Our findings demonstrate that biaxial strain can activate distinct electronic responses─metallicity, spin polarization, and inertness─to achieve precise differentiation of chemically similar nitrogen-containing species, establishing strained GeSe as a versatile and tunable platform for next-generation gas sensing.

Using quantum confinement and mixed halides has now enabled efficient blue to near-infrared perovskite light-emitting diodes (PeLEDs). However, achieving highly effective violet emission using these methods is challenging due to the inefficient radiative recombination and intrinsic phase segregation. Here we report an approach for violet PeLEDs with efficient radiative recombination and excellent spectral stability, by using B-site compositional engineering. By substituting Pb2+ with environmentally benign Sr2+, we fabricate films with tunable emission covering the spectral region from 400 to 500 nm. More importantly, this approach promotes the excitons converting from Wannier-Mott to Frenkel, known for its high exciton binding energy (Eb), which effectively accelerates the radiative recombination. The approach allows us to fabricate spectral stable violet perovskite films with photoluminescence quantum yields (PLQYs) exceeding 90% across the spectral region from 420 to 450 nm. Meanwhile, the incorporation of Sr2+ significantly suppresses ion migration while maintaining phase stability under severe circumstances. As a result, we achieve violet PeLED with a peak external quantum efficiency (EQE) of 0.69%, ranking as one of the most efficient violet PeLED reported to date. These findings provide valuable insights for advancing the development of violet PeLEDs.

The performance of a two-dimensional Schottky diode largely depends on its metal-semiconductor interfacial contact. However, the impact of the interfacial interaction type on the electrical performance remains elusive. Here, we reveal the role of the interfacial interaction type in rectifying behavior of lateral and vertical heterojunction Schottky diodes, taking the heterojunctions composed of two-dimensional metallic TaGe2P4 and semiconducting WSi2As4 with well-matched crystal structures and lattice constants as examples. The interfacial properties and rectification performance are comprehensively investigated using first-principles calculations. We find that the vertical heterojunction creates more obstructions for electron tunneling than the lateral counterpart due to the combined effect of the vertical and lateral Schottky barriers, thus leading to lower current and more conspicuous rectifying behavior. By tuning the metal-semiconductor relative length within the sub-5 nm diodes, the maximum rectification ratios of more than 105 and 107 are obtained for the lateral and vertical heterojunction diodes, respectively, comparable to those of traditional p-n junctions (105-107). The regulating mechanism is attributed to the variation in Schottky barrier width, which has a large impact on the reverse current while affects the forward current slightly, thus significantly regulating the rectification performance. These calculations provide a thorough understanding of the effect of interfacial properties on the rectification performance of lateral and vertical heterojunction rectifiers.

Achieving ultra-short channel field-effect transistors (FETs) that cater to both high-performance (HP) and low-power (LP) applications simultaneously is an unremitting pursuit in the field. Herein, employing first-principles calculations, we investigate the performance of sub-5 nm FETs based on the Janus MoSiGeN4 material and reveal the role of intrinsic out-of-plane electric polarization. We demonstrate that the synergistic effect of the intrinsic polarization field and the external electric field enhances the performance of Janus MoSiGeN4 FETs over MoSi2N4 and MoGe2N4 FETs. Our simulations show that a 3 nm gate-length cold-source Janus MoSiGeN4 FET, utilizing LaOCl as the dielectric material and an appropriate underlap structure, fulfills the HP and LP standards set by the International Technology Roadmap for Semiconductors (ITRS), with a subthreshold swing approaching the Boltzmann tyranny of 60 mV/dec. Notably, the optimized 1 nm gate-length MoSiGeN4 FET achieves an on-state current of 990 mu A/mu m (HP) and 690 mu A/mu m (LP), surpassing other theoretical two-dimensional FETs at the same gate length. Taking the defect effects into account, the MoSiGeN4 FET maintains a high on-state current that surpasses the ITRS for HP and LP standards. Our results provide a promising approach for designing ultra-short channel FETs suitable for both HP and LP applications. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Achieving precise control over charge transport through individual molecules is central to advancing single-molecule electronics. In short molecular junctions can exhibit rectification from fundamentally different mechanisms, yet strong sensitivity to contact geometry and electrode-molecule coupling often obscures whether diode behavior arises from asymmetric orbital alignment or quantum interference. Here, we demonstrate dual-mode rectification in a mechanically addressable metal-molecule-metal junction by chemically programming the interface with a heterofunctional scaffold bearing thiol and carboxyl anchors. Using scanning tunneling microscopy break-junction (STM-BJ) measurements under controlled mechanical modulation, we observe two reproducible conductance states that are most consistently assigned to two contact configurations on the basis of converging mechanical, statistical, and theoretical evidence. Current-voltage analysis further shows that the state assigned to the S-Au/COO-Au (thiolate-carboxylate) configuration rectifies through asymmetric molecular-orbital alignment and electrode coupling, whereas the state assigned to the nominally symmetric COO-Au/COO-Au (carboxylate-carboxylate) configuration rectifies via an interference-driven, bias-dependent Fano-resonance pathway. These findings demonstrate that anchored chemical synthons, combined with mechanical control of binding geometry, provide a practical strategy for engineering and directly comparing rectification mechanisms in short single-molecule junctions.

It is challenging to produce controllable localized magnetic fields (LMFs) at sub-nanometer scale, which is crucial to the designs of a nanoscale spin filter or spin logic gate. The quantum interferences (QIs) in molecular junctions containing cross and linear π-conjugated structures are studied by applying density functional theory (DFT) and nonequilibrium Green's function method as well as the effects of QIs on ring currents and LMFs produced in molecular junctions. Our calculations unveil that if the molecular junction contains a cyclic segment composed of both cross and linear π-conjugated units, the ring current and controllable nanoscale LMF (>6 mT) can be generated within the cyclic segment. Due to the destructive QI effect of the cross π-conjugated branch, the pathway selection takes place when electrons enter the ring circuit, which results in significant ring current and LMF. Improving the planarity of cyclic structures can effectively enhance ring currents and LMF.

Hydrostatic pressure provides a powerful external stimulus to modulate the excited-state properties of organic room-temperature phosphorescent (RTP) materials, yet the microscopic origin of pressure-induced spectral evolution remains insufficiently understood. Herein, we present a comprehensive theoretical investigation into the origin of blue-shifted RTP emission in IH-MPT under hydrostatic pressure. The calculations reveal that increasing pressure induces a pronounced blue shift in the phosphorescence spectrum, which originates from a continuous upward shift of the lowest triplet excited state (T1) energy level rather than aggregation or excimer effects. Structural analyses show that pressure progressively enhances molecular rigidity through packing densification and intramolecular planarization, effectively suppressing excited-state geometric relaxation. Consistently, the excited-state wave function becomes increasingly localized, accompanied by reduced vibronic coupling, decreased Huang-Rhys factors, and lower reorganization energies. Dimer calculations and Hirshfeld surface analyses further confirm that intermolecular electronic coupling is negligible and that the emission modulation is dominated by intrinsic monomer behavior reinforced by pressure-enhanced intermolecular constraints. Notably, an optimal pressure of approximately 16 GPa is identified, at which IH-MPT exhibits the bluest emission and simultaneously maximizes intersystem crossing and radiative decay rates. This optimal behavior arises from a synergistic balance between molecular rigidification and favorable energetic matching in the excited-state relaxation process, whereas excessive compression disrupts this balance and reduces emission efficiency. These results elucidate the mechanistic origin of pressure-regulated RTP emission and provide valuable insights into the rational control of phosphorescence through external pressure.

Isotope substitution is widely used to probe phonon behavior in hydrogen-rich materials, yet its effects on phonon dispersion remain difficult to access and poorly understood, particularly in low-dimensional systems. Here, using trans-polyacetylene (t-PA) as a prototypical model, we theoretically demonstrate tip-enhanced Raman scattering (TERS) imaging as a real-space approach for visualizing isotope effects on phonon dispersion. To enable a complete comparison between hydrogenated and deuterated t-PA, we access all optical phonon branches by activating the normally Raman-forbidden out-of-plane modes through the field-gradient effect. The newly resolved out-of-plane branches exhibit a crossing after deuteration, arising from their distinct wavevector-dependent isotope responses. By introducing the hydrogen-site mass participation factor, we show that phonon modes with stronger hydrogen-site motion undergo larger isotope-induced red shifts, whereas its wavevector-dependent variation governs dispersion reshaping and branch crossing. Moreover, Raman images directly visualize the deuteration-induced redistribution of vibrational amplitudes associated with hydrogen-site motions, thereby revealing the microscopic origin of isotope effects on phonon dispersion. These findings establish TERS imaging as a powerful real-space approach for visualizing isotope-dependent phonon behavior in low-dimensional molecular systems.

The design of new types of thermally activated delayed fluorescence (TADF) molecules has become a central research focus in recent years. Most TADF emitters consist of electron-donating and electron-withdrawing groups. In this work, we investigate the luminescent properties of all-donor molecules as potential TADF emitters using first-principles calculations. Our computational results confirm the experimental observation that the high luminescence efficiency of Cz2Bn arises from its relative large oscillator strength, and that TADF is enabled by a high-level reverse intersystem crossing (hRISC) process. Based on a systematic study of 53 all-donor molecules constructed from nine different donor groups, we find that most all-donor molecules exhibit a large energy gap (LEST) between the first singlet excited state (S1) and the first triplet excited state (T1), except for those incorporating strong electron-donating units. Molecules with strong donors can achieve TADF through RISC between T1 and S1. Those with moderate LEST values may exhibit TADF via hRISC from higher triplet excited states to S1. In contrast, molecules with large LEST generally struggle to exhibit TADF. Among the candidates, alldonor molecules containing DPA units show particularly promising potential as TADF emitters with high luminescence efficiency. Our computational study not only supports the existing experimental findings but also offers deeper insights into the design principles of this new class of TADF emitters.