Delayed room temperature phosphorescence enabled by phosphines.

Organic ultralong room-temperature phosphorescence (RTP) usually emerges instantly and immediately decays after excitation removal. Here we report a new delayed RTP that is postponed by dozens of milliseconds after excitation removal and decays in two steps including an initial increase in intensity followed by subsequent decrease in intensity. The delayed RTP is achieved through introduction of phosphines into carbazole emitters. In contrast to the rapid energy transfer from single-molecular triplet states (T1) to stabilized triplet states (Tn*) of instant RTP systems, phosphine groups insert their intermediate states (TM) between carbazole-originated T1 and Tn* of carbazole-phosphine hybrids. In addition to markedly increasing emission lifetimes by ten folds, since TM → Tn* transition require >30 milliseconds, RTP is thereby postponed by dozens of milliseconds. The emission character of carbazole-phosphine hybrids can be used to reveal information through combining instant and delayed RTP, realizing multi-level time resolution for advanced information, biological and optoelectronic applications.

Interaction between hypertension and frailty and their impact on death risk in older adults: a follow-up study.

BACKGROUND: Hypertension and frailty often occur concurrently, exhibiting increasing prevalence in the older population. In this study, we analyzed the frailty status among older adults with hypertension and the impact of their interaction on death risk. METHOD: This prospective cohort survey study included data from older people in an urban community in Beijing collected between 2009 and 2020 using the cluster random sampling method. The participants were older adults who were ≥ 60 years old at the time of investigation and had lived at the place of investigation for > 1 year. The survey variables comprised those related to health and frailty status assessed during the 2009 baseline survey, along with death-related information as outcome variables in 2020. Additionally, a frailty index (FI) model was used to examine the frailty status among the older adults at baseline. The effects of hypertension prevalence on the age-related frailty changes as well as on mortality for varying degrees of frailty were further analyzed. Lastly, Cox regression and Kaplan-Meier curves were applied to evaluate the impact of the interaction between hypertension and frailty on death risk. RESULTS: Ultimately, 1197 older individuals aged between 60 and 101 years(average age at baseline: 74.8 ± 8.6 years) were included .Among them, 475 individuals were men (mean age:74.8 ± 8.8 years), and 722 were women (mean age:74.8 ± 8.4 years).Frailty was identified in 151 individuals, leading to a prevalence rate of 12.6%(151/1197),while hypertension was detected in 593 (prevalence rate:49.5% [593/1197]).A total of 443 deaths were recorded by 2020, resulting in a mortality rate of 37.0% (443/1197).Moreover, FI values and mortality rates were higher at any age in older adults with hypertension compared with those without hypertension. Survival time analysis showed that the median survival time of older adults with hypertension and frailty was the shortest (39.0[95%CI: 35.6-42.3] months)when compared with that of older adults without hypertension but with frailty (52.9 [95%CI: 46.6-59.3] months), those with hypertension but without frailty (102.7 [95%CI: 98.7-106.8] months), and those without hypertension and frailty (127.9 [95%CI: 113.5-134.7] months),with log-rank x2 = 999.686 and P < 0.001. Furthermore, Cox regression results demonstrated that older adults with hypertension and frailty had the highest death risk when compared with that of older adults without hypertension and frailty (HR = 1.792, P < 0.001), those without hypertension but with frailty (HR = 1.484, P < 0.001), and those with hypertension but without frailty (HR = 1.406, P = 0.005). CONCLUSION: Frailty is prevalent among older adults with hypertension; however, older adults with both hypertension and frailty have a relatively higher mortality risk. Therefore, screening and assessment of frailty in the older population with hypertension are crucial for its early identification, thereby enabling timely and appropriate interventions to prevent or delay the adverse effects of this concurrent condition.

Allochroic cluster light-emitting diodes based on unique µ3-tetraphosphine Cu3X3 crowns with tunable excited states.

Multicomponent excited states endow copper iodide clusters with allochroic properties under diverse stimuli. However, crystal states are required, and cluster stimulus sensitivity hampers electroluminochromism. We developed PhQPCu3X3 (X = Cl, Br, and I) with the first µ3-bridging tetraphosphine ligand, whose Cu3X3 crowns were exposed to external stimulus. The increased proportion of Cu3X3 results in equal contributions of cluster- and ligand-centered components to excited states, the former of which is highly sensitive to grind, vapor, and, especially, electric stimuli, due to semi-exposed Cu3X3. Through vacuum evaporation and vapor fumigation of cluster-based emissive layers, the diodes' electroluminescence colors changed from yellow to white. Joule heat during device operation induced further color variation to orange, corresponding to Commission Internationale de l'Eclairage coordinates of PhQPCu3I3 changed from (0.44 ± 0.1, 0.34 ± 0.1) to (0.57 ± 0.1, 0.42 ± 0.1). These results demonstrate the superiority of luminescent clusters in accurate excited-state modulation, holding promise for wide applications.

Bulk Passivation Enables Hundredfold-Enhanced Electroluminescence of Monophosphine Cu4 I4 Cubes.

Electroluminescent (EL) clusters emerged rapidly, owing to their organic-inorganic hybrid character useful for comprehensive performance integration and the potential for large-scale display and lighting applications. However, despite their good photoluminescent (PL) properties, until present, no efficient EL monodentate ligand-based clusters were reported due to structural variation during processing and excitation and exciton confinement on cluster-centered quenching states. Here we demonstrate an effective bulky passivation strategy for efficient cluster light-emitting diodes with a monophosphine Cu4 I4 cube named [TMeOPP]4 Cu4 I4 . With terminal pyridine groups, an active matrix named TmPyPB supports an effective host-cluster interplay for configuration fixation, structural stabilization, and exciton-confinement optimization. Compared to common inactive hosts, the passivation effects of TmPyPB markedly reduce trap-state densities by 24-40 % to suppress nonradiative decay, resulting in state-of-the-art PL and EL quantum yields reaching 99 % and 15.6 %, respectively, which are significantly improved by about 7-fold. TmPyPB simultaneously increases EL luminance to 104 nits, which is ≈100-fold that of the non-doped analogue.

Phosphine-Oxide-Balanced Intra- and Interchain Through-Space Charge Transfer in Thermally Activated Delayed Fluorescence Polymers: Beyond 30% External Quantum Efficiency.

Through-space charge transfer (TSCT) is crucial for developing highly efficient thermally activated delayed fluorescence polymers. The balance of intra- and interchain TSCT can markedly improve performance, but it is still a big challenge. In this work, an effective strategy for "intra- and interchain TSCT balance" is demonstrated by way of a series of non-conjugated copolymers containing a 9,9-dimethylacridine donor and triazine-phosphine oxide (PO)-based acceptors. Steady-state and transient emission spectra indicate that compared to the corresponding blends, the copolymers can indeed achieve balanced intra- and interchain TSCT by accurately optimizing the inductive and steric effects of the acceptors. The DPOT acceptor with the strongest electron-withdrawing ability and the second bigger steric hindrance endows its copolymers with state-of-the-art photoluminescence and electroluminescence quantum efficiencies beyond 95% and 32%, respectively. This demonstrates that, compared to other congeners, the synergistic inductive and steric effects effectively enhance TSCT in DPOT-based copolymers for radiation, and suppress singlet and triplet quenching. The record-high efficiencies of its devices make this kind of copolymers hold the potential for low-cost, large-scale, and high-efficiency applications.

Interfacial Passivation Enormously Enhances Electroluminescence of Triphenylphosphine Cu4 I4 Cube.

Defect is one of the key factors limiting optoelectronic performances of organic-inorganic hybrid systems. Although high-efficiency bidentate ligands based electroluminescent (EL) clusters reported, until present, only few EL clusters based on monodentate ligands are realized since their structural instability induces more surface/interface defects. Herein, this bottleneck is first overcome in virtue of interfacial passivation by electron transporting layers (ETL). Through using TmPyPB with meta-linked pyridines as ETL, photoluminescent (PL) and EL quantum efficiencies of the simplest monophosphine Cu4 I4 cube [TPP]4 Cu4 I4 are greatly improved by ≈2 and 23 folds, respectively, as well as ≈200 folds increased luminance, corresponding to a huge leap from nearly unlighted (<20 nits) to highly bright (>3000 nits). The passivation effect of TmPyPB on surface defects of cluster layer is embodied as preventing interfacial charge trapping and suppressing exciton nonradiation.

Cluster Light-Emitting Diodes Containing Copper Iodine Cube with 100 % Exciton Utilization Using Host-Cluster Synergy.

Clusters combine the advantages of organic molecules and inorganic nanomaterials, which are promising alternatives for optoelectronic applications. Nonetheless, recently emerged cluster light-emitting diodes require further excited state optimization of cluster emitters, especially to reduce population of the cluster-centered triplet quenching state (3 CC). Here we report that redox-active ligands enhance reverse intersystem crossing (RISC) of Cu4 I4 cluster for triplet-to-singlet conversion, and thermally activated delayed fluorescence (TADF) host can provide an external RISC channel. It indicates that the complementarity between TADF host and cluster in RISC transitions gives rise to 100 % triplet conversion efficiency and complete singlet exciton convergence, rendering 100-fold increased singlet radiation rate constant and tenfold decreased triplet non-radiation rate constant. We achieve a photoluminescence quantum yield of 99 % and a record external quantum efficiency of 29.4 %.

Integrating Asymmetric O-B-N Unit in Multi-Resonance Thermally Activated Delayed Fluorescence Emitters towards High-Performance Deep-Blue Organic Light-Emitting Diodes.

Developing deep-blue thermally activated delayed fluorescence (TADF) emitters with both high efficiency and color purity remains a formidable challenge. Here, we proposed a design strategy by integrating asymmetric oxygen-boron-nitrogen (O-B-N) multi-resonance (MR) unit into traditional N-B-N MR molecules to form a rigid and extended O-B-N-B-N MR π-skeleton. Three deep-blue MR-TADF emitters of OBN, NBN and ODBN featuring asymmetric O-B-N, symmetric N-B-N and extended O-B-N-B-N MR units were synthesized through the regioselective one-shot electrophilic C-H borylation at different positions of the same precursor. The proof-of-concept emitter ODBN exhibited respectable deep-blue emission with Commission International de l'Eclairage coordinate of (0.16, 0.03), high photoluminescence quantum yield of 93 % and narrow full width at half maximum of 26 nm in toluene. Impressively, the simple trilayer OLED employing ODBN as emitter achieved a high external quantum efficiency up to 24.15 % accompanied by a deep blue emission with the corresponding CIE y coordinate below 0.1.

Deep-Blue Electroluminescence from Phosphine-Stabilized Au3 Triangles and Au3 Ag Pyramids.

The optoelectronic applications of clusters emerged rapidly. Cluster light-emitting diodes (CLED) as representative hold promise as a new generation of displays and lightings. However, as one of the main challenges in electroluminescence (EL) field, until present, no deep-blue CLEDs were reported, due to the strict requirements on excited-state characteristics of clusters. Herein, two phosphine-stabilized Au3 triangle and Au3 Ag pyramid named [O(Audppy)3 ]BF4 and [O(Audppy)3 Ag](BF4 )2 were chosen to demonstrate efficient deep-blue CLEDs. The ligand-incorporated charge transfer transitions of the clusters contribute to both singlet and triplet excited states of the clusters, giving rise to phosphorescence at 460 nm and EL emissions at 436 nm. Based on device engineering, the maximum luminescence beyond 8000 nits and the chromatic coordinates with y <0.1 in deep-blue region verify the competence of CLEDs for high-resolution displays.

Synergetic Insulation and Induction Effects Selectively Optimize Multiresonance Thermally Activated Delayed Fluorescence.

Multiresonance (MR) emitters featuring narrowband emissions and theoretically 100% exciton harvesting are great potential for organic light-emitting diode (OLED) applications. However, how to functionalize MR molecules without scarifying emission color purity is still a key challenge. Herein, we report a feasible strategy for selective optimization of MR molecules, which is demonstrated by a blue MR emitter tCBNDASPO substituted with a diphenylphosphine oxide (DPPO) group. Compared to its DPPO-free parent molecule, tCBNDASPO preserves narrowband feature with full widths at half maximum (FWHM) values of 28 nm in film and 32 nm in OLEDs and achieves 40% increased photoluminescence (92%) and electroluminescence quantum efficiencies (28%). It is showed that insulation effect of P=O effectively confines the singlet excited state on MR core to keep emission color purity, and its induction effect enhances singlet radiation and triplet-to-singlet conversion. This synergism for selective optimization is based on rational linkage between MR core and functional groups.

Overcoming Efficiency Limitation of Cluster Light-Emitting Diodes with Asymmetrically Functionalized Biphosphine Cu4I4 Cubes.

Electroluminescent (EL) nanoclusters holding promise for new-generation cluster light-emitting devices (CLEDs) rapidly emerge. However, slow radiation and serious quenching of cluster emitters largely limit the device performance. Herein, we report two monofunctionalized biphosphine chelated Cu4I4 clusters [DMACDBFDP]2Cu4I4 and [DPACDBFDP]2Cu4I4. The asymmetric modification and electron-donating effect of acridine groups lead to the iodine-to-ligand charge transfer predominant excited states of the clusters, which feature thermally activated delayed fluorescence with markedly improved singlet radiative rate constants and reduced triplet nonradiative rate constants. As consequence, compared to the nonfunctionalized parent cluster, [DPACDBFDP]2Cu4I4 achieves 16-fold increased photoluminescence (81%) and 20-fold increased EL (19.5%) quantum efficiencies. Such new-record efficiencies make CLEDs achieve the state-of-the-art performance of all kinds of EL technologies.

Ambipolar Self-Host Functionalization Accelerates Blue Multi-Resonance Thermally Activated Delayed Fluorescence with Internal Quantum Efficiency of 100.

Emerging multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitters can combine 100% exciton harvesting and high color purity for their organic light-emitting diodes (OLED). However, the highly planar configurations of MR molecules lead to intermolecular-interaction-induced quenching. A feasible way is integrating host segments into MR molecules, namely a "self-host" strategy, but without involving additional charge transfer and/or vibrational components to excited states. Herein, an ambipolar self-host featured MR emitter, tCBNDADPO, is demonstrated, whose ambipolar host segment (DADPO) significantly and comprehensively improves the TADF properties, especially greatly accelerated singlet radiative rate constant of 2.11 × 108 s-1 and exponentially reduced nonradiative rate constants. Consequently, at the same time as preserving narrowband blue emission with an FWHM of ≈28 nm at a high doping concentration of 30%, tCBNDADPO reveals state-of-the-art photoluminescence and electroluminescence quantum efficiencies of 99% and 30%, respectively. The corresponding 100% internal quantum efficiency of tCBNDADPO supported by an ultrasimple trilayer and heavily doped device demonstrates the feasibility of the ambipolar self-host strategy for constructing practically applicable MR materials.

Combined effect of diabetes and frailty on mortality among Chinese older adults: A follow-up study.

Background: Frailty and diabetes are two important health problems associated with aging in older individuals. This paper seeks to analyze the frailty in older adults suffering from diabetes and the combined effect of diabetes and frailty on mortality risk. Methods: The frailty index (FI) model was employed when evaluating frailty among the older adults based on the baseline data conducted in 2009; and death as outcome variables collected in 2020 were analyzed. The influence of diabetes on age-related changes in frailty in the older adults and resulting mortality rates was analyzed. Cox regression and Kaplan-Meier curves were applied to evaluate the influence on the risk of death and the 11-year survival of the older adults with varying diabetes and frailty statuses. Results: Ultimately, 1,213 older people aged between 60 and 101, with an average age of (74.79 ± 8.58) at baseline, were included in the analysis. By 2020, there had been 447 deaths with mortality at 36.9% (447/1,213); there were 271 cases of diabetes, with a prevalence of 22.3% (271/1,213). The mean FI value for older adults with diabetes was higher than that of those without regardless of age, and the average annual relative growth rate of the FI value for older adults with diabetes was higher than that of those without diabetes (ß = 0.039 vs. ß = 0.035, t = 8.367, P < 0.001). For all FI value levels, the mortality rate among older adults with diabetes was higher than that of those without. The Cox Regression analysis showed that, compared with those suffering from neither diabetes nor frailty, older adults with both had the higher mortality risk (HR = 1.760. P < 0.001), followed by older adults suffering from frailty alone (HR = 1.594, P = 0.006), and then by older adults suffering from only diabetes (HR = 1.475, P = 0.033). The survival analysis showed that the median survival of those suffering from diabetes and frailty to be the shortest at just 57.23 (95% CI: 54.05 to 60.41) months, lower than the 83.78 (95% CI: 79.33 to 88.23) months in those suffering from frailty alone, and 119.93 (95% CI: 113.84 to 126.02) months in those with only diabetes, and 124.39 (95% CI: 119.76 to 129.02) months in older adults with neither diabetes nor frailty (P < 0.001). Conclusion: Frailty is common among older adults suffering from diabetes, and there is an increased risk of poor health outcomes, such as death, among older adults suffering from diabetes and frailty. When diagnosing, treating, and dealing with older adults with diabetes, attention should be paid to screening and assessing frailty in hopes of identifying it early so that appropriate measures of intervention can be taken to avoid or delay the resulting adverse effects.

Frailty Status Among the Elderly of Different Genders and the Death Risk: A Follow-Up Study.

Background: Frailty in the elderly population is currently a frontier and focus in the field of health and aging. The goal of this study was to explore the frailty status among the elderly of different genders and its influence on the risk of death during 11 years. Methods: Frailty index (FI) was used to evaluate the frailty status in the elderly based on the baseline data conducted in 2009; and death as outcome variables collected in 2020 were analyzed. The difference of the frailty level and mortality of different genders was compared. Cox regression and Kaplan-Meier curves were applied to evaluate the influence on the risk of death and the 11-year survival of the elderly at different level of frailty, respectively. Results: Totally, 1,246 elderly people were recruited. The mortality in men (43.7%, 227/519) was statistically higher than that in women (34.3%, 249/727) (x 2 = 11.546, P = 0.001). Deficits accumulated exponentially with age, and at all ages, women accumulated more deficits than do men on average (B = 0.030 vs. 0.028, t = 4.137, P = 0.023). For any given level of frailty, the mortality rate is higher in men than in women, and the difference in mortality between genders reached the peak when FI value was 0.26. Cox regression analysis showed that FI value had a greater impact on the risk of death in older men (HR = 1.171, 95%CI: 1.139~1.249)than that in older women (HR = 1.119, 95%CI: 1.039~1.137). Survival analysis showed that the median 11-year survival time in women was longer than that in men (95.26 vs. 89.52 months, Log rank = 9.249, P = 0.002). Kaplan-Meier curves showed that the survival rate decreased with the increase of frailty, and at the same level of frailty, survival time in older women was longer than that in older men, except for severe frailty (FI ≥ 0.5). Conclusion: The frailty status and its influence on mortality are different among the older people of different genders; therefore, specific interventions for frailty should be conducted in the elderly population of different genders, as well as of different degrees of frailty.

Ladder-like energy-relaying exciplex enables 100% internal quantum efficiency of white TADF-based diodes in a single emissive layer.

Development of white organic light-emitting diodes based on purely thermally activated delayed fluorescence with a single-emissive-layer configuration has been a formidable challenge. Here, we report the rational design of a donor-acceptor energy-relaying exciplex and its utility in fabricating single-emissive-layer, thermally activated delayed fluorescence-based white organic light-emitting diodes that exhibit 100% internal quantum efficiency, 108.2 lm W-1 power efficiency, and 32.7% external quantum efficiency. This strategy enables thin-film fabrication of an 8 cm × 8 cm thermally activated delayed fluorescence white organic light-emitting diodes (10 inch2) prototype with 82.7 lm W-1 power efficiency and 25.0% external quantum efficiency. Introduction of a phosphine oxide-based acceptor with a steric group to the exciplex limits donor-acceptor triplet coupling, providing dual levels of high-lying and low-lying triplet energy. Transient spectroscopic characterizations confirm that a ladder-like energy relaying occurs from the high-lying triplet level of the exciplex to a blue emitter, then to the low-lying triplet level of the phosphine oxide acceptor, and ultimately to the yellow emitter. Our results demonstrate the broad applicability of energy relaying in multicomponent systems for exciton harvesting, providing opportunities for the development of third-generation white organic light-emitting diode light sources.

High-efficiency hyperfluorescent white light-emitting diodes based on high-concentration-doped TADF sensitizer matrices via spatial and energy gap effects.

Despite the success of monochromatic hyperfluorescent (HF) organic light-emitting diodes (OLEDs), high-efficiency HF white OLEDs (WOLEDs) are still a big challenge. Herein, we demonstrate HF WOLEDs with state-of-the-art efficiencies, featuring a quasi-bilayer emissive layer (EML) composed of an ultrathin (0.1 nm) blue fluorescence (FL) emitter (TBPe) layer and a layer of thermally activated delayed fluorescence (TADF) sensitizer matrix heavily doped with a yellow FL emitter (TBRb, 3%). Based on an asymmetric high-energy-gap TADF sensitizer host (PhCzSPOTz), such an "ultrathin blue emitting layer (UTBL)" strategy endowed the HF WOLEDs with a record power efficiency of ∼80 lm W-1, approaching the level of fluorescent tubes. Transient photoluminescence (PL) and electroluminescence (EL) kinetics demonstrate that the spatial separation of TBPe from the TADF sensitizer and TBRb, and the large energy gap between the latter two effectively suppress triplet leakage, in addition to suppressing triplet diffusion in the PhCzSPOTz matrix with anisotropic intermolecular interactions. These results provide a new insight into the exciton allocation process in HF white light-emitting systems.

Highly Efficient and Color-Stable Thermally Activated Delayed Fluorescence White Light-Emitting Diodes Featured with Single-Doped Single Emissive Layers.

Despite their merits of environmental friendliness, low cost, and large-scale production, thermally activated delayed fluorescence (TADF) based white organic light-emitting diodes (WOLEDs) for daily lighting applications still face the formidable challenges of structural simplification and controllable exciton allocation. Here, the state-of-the-art full-TADF WOLEDs with features of the single-doped single emissive layers (EMLs) and ultrasimple trilayer structure are demonstrated. The EMLs are binary systems as yellow TADF emitter (4CzTPNBu) doped blue TADF matrix (ptBCzPO2 TPTZ) with the large steric hindrance and mismatched frontier molecular orbital energy levels to effectively restrain excessive blue-to-yellow triplet exciton transfer and host-dopant interaction induced triplet quenching. Simultaneously, Förster resonance energy transfer is utilized to optimize exciton allocation for the balance of blue and yellow emissions, giving rise to the photoluminescence quantum yield beyond 90%. Consequently, these single-doped EMLs endow their cool white, pure white, and warm white diodes with the high-quality and ultrastable white light and the 100% exciton utilization efficiencies through the extremely simple structures, making them competent for the diverse daily lighting applications.

Enhancing Reverse Intersystem Crossing via Secondary Acceptors: toward Sky-Blue Fluorescent Diodes with 10-Fold Improved External Quantum Efficiency.

How to simply but effectively facilitate reverse intersystem crossing (RISC) transition is always the key issue for developing high-performance thermally activated delayed fluorescence dyes. In this work, as a proof of concept, a feasible strategy named "acceptor enhancement" is demonstrated with a series of ternary blue emitters ( xCz mPO nTPTZ) using diphenylphosphine oxide (PO) as secondary acceptors. Compared with its PO-free binary analogue, such a simple introduction of PO groups in pCzPO2TPTZ dramatically enhances its RISC rate constant ( kRISC) by 10 times the level of ∼105 s-1, accompanied by RISC efficiency (ηRISC) of 92%, which further improves the triplet-to-singlet upconversion for effective triplet harvesting in its devices. As a result, on the basis of a trilayer device structure, pCzPO2TPTZ realized a state-of-the-art external quantum efficiency beyond 20% with a 10-fold improvement.

Secondary Acceptor Optimization for Full-Exciton Radiation: Toward Sky-Blue Thermally Activated Delayed Fluorescence Diodes with External Quantum Efficiency of ≈30.

Efficient blue emitters are indispensable for organic light-emitting diodes (OLEDs) with respect to display and lighting applications. Because of their high-energy excited states, both radiation enhancement and non-radiation suppression should be simultaneously optimized to realize 100% exciton utilization. Here, it is shown that the excited-state characteristics of blue thermally activated delayed fluorescence emitters can be precisely controlled by a secondary acceptor having moderate electronic effects on increasing the singlet charge-transfer component and preserving the triplet locally excited-state component. In addition of planar configuration between the donor and the primary acceptor, the radiative transition improvement and non-radiative transition suppression can be simultaneously achieved for "full-exciton radiation". A molecule using diphenylphosphine oxide as the secondary acceptor exhibits ≈100% photoluminescence quantum yield on the basis of its tenfold increased singlet radiative rate constant, fivefold decreased singlet and triplet non-radiative rate constants, and ≈100% reverse intersystem crossing efficiency, which further endows ≈100% exciton utilization efficiency to its sky-blue OLEDs.

Allochroic thermally activated delayed fluorescence diodes through field-induced solvatochromic effect.

Allochroic organic light-emitting devices (AOLEDs) characterized by field-dependent emissive color variation are promising as visible signal response units for intelligent applications. Most of the AOLEDs were realized by changing their recombination zones or inter- and intramolecular energy transfer, rendering the limited repeatability, stability, and electroluminescence (EL) performance. We report a novel thermally activated delayed fluorescence (TADF) diode that featured a successive and irreversible emission color change from bluish green to deep blue during voltage increase, which uses the significant influence of host polarity on the emission color of TADF dyes, namely, solvatochromic effect. Its host 3,6-di-tert-butyl-1,8-bis(diphenylphosphoryl)-9H-carbazole (tBCzHDPO) was designed with remarkable field-dependent polarity reduction from 7.9 to 3.3 D by virtue of hydrogen bond-induced conformational isomerization. This TADF device achieves the best EL performance among AOLEDs, to date, with, for example, an external quantum efficiency beyond 15%, as well as the unique irreversible allochroic characteristic for visible data storage and information security.