Direct identification of interfacial degradation in blue OLEDs using nanoscale chemical depth profiling.

Understanding the degradation mechanism of organic light-emitting diodes (OLED) is essential to improve device performance and stability. OLED failure, if not process-related, arises mostly from chemical instability. However, the challenges of sampling from nanoscale organic layers and interfaces with enough analytical information has hampered identification of degradation products and mechanisms. Here, we present a high-resolution diagnostic method of OLED degradation using an Orbitrap mass spectrometer equipped with a gas cluster ion beam to gently desorb nanometre levels of materials, providing unambiguous molecular information with 7-nm depth resolution. We chemically depth profile and analyse blue phosphorescent and thermally-activated delayed fluorescent (TADF) OLED devices at different degradation levels. For OLED devices with short operational lifetimes, dominant chemical degradation mainly relate to oxygen loss of molecules that occur at the interface between emission and electron transport layers (EML/ETL) where exciton distribution is maximised, confirmed by emission zone measurements. We also show approximately one order of magnitude increase in lifetime of devices with slightly modified host materials, which present minimal EML/ETL interfacial degradation and show the method can provide insight for future material and device architecture development.

Critical role of electrons in the short lifetime of blue OLEDs.

Designing robust blue organic light-emitting diodes is a long-standing challenge in the display industry. The highly energetic states of blue emitters cause various degradation paths, leading to collective luminance drops in a competitive manner. However, a key mechanism of the operational degradation of organic light-emitting diodes has yet to be elucidated. Here, we show that electron-induced degradation reactions play a critical role in the short lifetime of blue organic light-emitting diodes. Our control experiments demonstrate that the operational lifetime of a whole device can only be explained when excitons and electrons exist together. We examine the atomistic mechanisms of the electron-induced degradation reactions by analyzing their energetic profiles using computational methods. Mass spectrometric analysis of aged devices further confirm the key mechanisms. These results provide new insight into rational design of robust blue organic light-emitting diodes.

Post-Traumatic Growth of Nurses in COVID-19 Designated Hospitals in Korea.

BACKGROUND: This descriptive survey aimed to identify the factors affecting the post-traumatic growth (PTG) of nurses in COVID-19 designated hospitals on the basis of a PTG model. METHODS: A survey of 250 nurses working at three COVID-19 hospitals in Seoul, South Korea, was conducted from May to July 2021. The collected data were analyzed using the IBM SPSS 25 (IBM Inc., Armonk, NY, USA). RESULTS: The participants in this study were mostly women (92.7%), and the average age and career duration were 32.08 and 7.88 years, respectively. The factors that significantly influenced the participants' PTG were identified as marriage, religion, self-disclosure, deliberate rumination, meaning in life, and resilience. CONCLUSIONS: As new infectious diseases emerge, it is necessary to develop a program that can encourage self-disclosure and deliberate rumination, help nurses discover and pursue meaning in life, and enhance their ability to overcome trauma and promote PTG.

Spiritual needs among Koreans and Americans with advanced chronic illnesses: A cultural comparison.

AIMS AND OBJECTIVES: This study aimed to measure the frequency of spiritual needs, identify the factors associated with these needs among Korean and American persons living with an advance chronic illness and compare them from a cross-cultural perspective. BACKGROUND: Persons with serious or life-limiting illnesses often have spiritual needs. Unmet spiritual needs are associated with poor well-being and threaten psychological health. Little is known about how specific spiritual needs vary across cultures. DESIGN: A quantitative, cross-sectional, observational cross-cultural comparison was undertaken. METHODS: The study has been prepared in accordance with the STROBE guidelines. Convenience sampling was used to recruit participants from outpatient clinics in South Korea and Southern California (N = 202). Spiritual needs were measured using the Spiritual Interests Related to Illness Tool (SpIRIT); demographic and illness-related variables were also assessed using paper-and-pencil questionnaires. Data were analysed using various parametric statistical tests, including multiple regression analysis. RESULTS: The findings quantify the intensity and types of spiritual needs that persons living with an advanced chronic illness experience. Furthermore, they show how the spiritual needs of religiously diverse samples of South Koreans and Americans differ. The findings also indicate that self-reported spirituality and religiosity independently explain a substantial amount of the variance in spiritual needs. CONCLUSIONS: In both the samples, spiritual needs were reported and associated with spirituality and religiosity. Although all the eight domains of spiritual needs assessed by the SpIRIT were pertinent to the Korean and American samples, they were prioritised differently. RELEVANCE TO CLINICAL PRACTICE: Screening patients to ascertain how important spirituality or religiosity is to them may help clinicians focus their in-depth assessments on those who report high levels of spirituality or religiosity because these patients may experience the strongest spiritual needs. The SpIRIT shows promise as a measure of diverse spiritual needs.

Improved Efficiency and Lifetime of Deep-Blue Hyperfluorescent Organic Light-Emitting Diode using Pt(II) Complex as Phosphorescent Sensitizer.

Although the organic light-emitting diode (OLED) has been successfully commercialized, the development of deep-blue OLEDs with high efficiency and long lifetime remains a challenge. Here, a novel hyperfluorescent OLED that incorporates the Pt(II) complex (PtON7-dtb) as a phosphorescent sensitizer and a hydrocarbon-based and multiple resonance-based fluorophore as an emitter (TBPDP and ν-DABNA) in the device emissive layer (EML), is proposed. Such an EML system can promote efficient energy transfer from the triplet excited states of the sensitizer to the singlet excited states of the fluorophore, thus significantly improving the efficiency and lifetime of the device. As a result, a deep-blue hyperfluorescent OLED using a multiple resonance-based fluorophore (ν-DABNA) with Commission Internationale de L'Eclairage chromaticity coordinate y below 0.1 is demonstrated, which attains a narrow full width at half maximum of ≈17 nm, fourfold increased maximum current efficiency of 48.9 cd A-1 , and 19-fold improved half-lifetime of 253.8 h at 1000 cd m-2 compared to a conventional phosphorescent OLED. The findings can lead to better understanding of the hyperfluorescent OLEDs with high performance.

Effect of Planarity of Aromatic Rings Appended to o-Carborane on Photophysical Properties: A Series of o-Carboranyl Compounds Based on 2-Phenylpyridine- and 2-(Benzo[b]thiophen-2-yl)pyridine.

Herein, we investigated the effect of ring planarity by fully characterizing four pyridine-based o-carboranyl compounds. o-Carborane was introduced to the C4 position of the pyridine rings of 2-phenylpyridine and 2-(benzo[b]thiophen-2-yl)pyridine (CB1 and CB2, respectively), and the compounds were subsequently borylated to obtain the corresponding CN-chelated compounds CB1B and CB2B. Single-crystal X-ray diffraction analysis of the molecular structures of CB2 and CB2B confirmed that o-carborane is appended to the aryl moiety. In photoluminescence experiments, CB2, but not CB1, showed an intense emission, assignable to intramolecular charge transfer (ICT) transition between the aryl and o-carborane moieties, in both solution and film states. On the other hand, in both solution and film states, CB1B and CB2B demonstrated a strong emission, originating from π-π * transition in the aryl groups, that tailed off to 650 nm owing to the ICT transition. All intramolecular electronic transitions in these o-carboranyl compounds were verified by theoretical calculations. These results distinctly suggest that the planarity of the aryl groups have a decisive effect on the efficiency of the radiative decay due to the ICT transition.

2-Phenylpyridine- and 2-(benzo[b]thiophen-2-yl)pyridine-based o-carboranyl compounds: impact of the structural formation of aromatic rings on photophysical properties.

2-Phenylpyridine- and 2-(benzo[b]thiophen-2-yl)pyridine-based (ppy- and btp-based) o-carboranyl (Car1 and Car2) and their B(CH3)2-C∧N-chelated (Car1B and Car2B) compounds were prepared and fully characterised by multinuclear NMR spectroscopy and elemental analysis. The solid-state structure of Car2B was determined by single-crystal X-ray diffraction, which revealed a four-coordinated dimethylboryl centre. All compounds displayed major absorption bands that were assigned to π-π* transitions involving the ppy and btp moieties, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carboranes and their aryl groups. Furthermore, the chelated compounds exhibited dominant low-energy absorption bands (λabs = 333 nm for Car1B and 383 nm for Car2B) resulting from the reinforcement of ICT transitions that correspond to the o-carborane moieties through the restriction of aromatic-ring free rotation. While Car1 and Car2 did not exhibit photoluminescence emissions in toluene at 298 K, Car1B and Car2B showed intense emissions, which are assignable to π-π* transitions associated with each chelated aryl group. However, Car1 and Car2 evidently emitted at around 450 nm in solution at 77 K, invoked by radiative ICT transitions between the carborane and the ppy or btp moiety, indicating that ICT-based radiative decay is only invigorated in the rigid state in the absence of structural variations, such as C-C bond fluctuations in the carborane cage and aromatic-ring free rotation. Interestingly, while Car1 in the film state exhibited a weak ICT-based emission spectrum, and Car1B and Car2B showed intense emissions originating from π-π* transitions associated with each chelated aryl group, Car2 showed significantly enhanced emissions in the same energy region as that exhibited in solution at 77 K, resulting in a much larger quantum efficiency over that in solution. DFT-optimised structures of Car1 and Car2 in their ground and the first-excited states clearly reveal that the enhanced emissive features of Car2 in the film state are strongly associated with the retained planarity of the btp moiety in both the ground and excited states. The photophysical results for these o-carboranyl compounds definitively reveal that the planarities of the aryl groups appended to the o-carborane decisively affect the efficiency of radiative decay based on ICT involving the o-carborane.

Degradation of blue-phosphorescent organic light-emitting devices involves exciton-induced generation of polaron pair within emitting layers.

Degradation of organic materials is responsible for the short operation lifetimes of organic light-emitting devices, but the mechanism by which such degradation is initiated has yet to be fully established. Here we report a new mechanism for degradation of emitting layers in blue-phosphorescent devices. We investigate binary mixtures of a wide bandgap host and a series of novel Ir(III) complex dopants having N-heterocyclocarbenic ligands. Our mechanistic study reveals the charge-neutral generation of polaron pairs (radical ion pairs) by electron transfer from the dopant to host excitons. Annihilation of the radical ion pair occurs by charge recombination, with such annihilation competing with bond scission. Device lifetime correlates linearly with the rate constant for the annihilation of the radical ion pair. Our findings demonstrate the importance of controlling exciton-induced electron transfer, and provide novel strategies to design materials for long-lifetime blue electrophosphorescence devices.

Through-space charge transfer and emission color tuning of di-o-carborane substituted benzene.

1,4-Di-(1-Ar-o-carboran-2-yl)benzene (Ar = 3,5-bis(trifluoromethyl)phenyl (1), phenyl (2), 4-n-butylphenyl (3), 4-N,N-dimethylaniline (4)) compounds that are electronically modulated at the C1-position of o-carborane with the electron-withdrawing or -donating aryl groups were prepared and characterized. The X-ray crystal structures of 1, 3, and 4 reveal that the two aryl groups on the C1-carborane carbon atoms are oppositely positioned, featuring overall C2-symmetry, and the C1-C2 bond length of carborane increases with the increasing order of electron-donating effect of an aryl group. UV-vis absorption spectra exhibit small low-energy absorption bands at around 275-300 nm for 1-3 while 4 shows a broad absorption tail at 350-400 nm. Although 1-4 show virtually no emission in solution, an intense aggregation-induced emission over the region ranging from 400-700 nm is observed in the solid state. Importantly, the emission wavelengths of 1-4 exhibit an apparent red-shift upon changing the aryl substituent from the CF3 to the NMe2 group (from 1 to 4). TD-DFT calculations suggest that the low-energy electronic transition is attributed to the intramolecular "through-space" charge transfer between the appended aryl group (HOMO) and the central phenylene ring (LUMO), and the greater change in the HOMO level by the substituent than that in the LUMO is responsible for the emission color tuning.

Deep red phosphorescence of cyclometalated iridium complexes by o-carborane substitution.

Heteroleptic (C(∧)N)2Ir(acac) (C(∧)N = 5-MeCBbtp (5a); 4-BuCBbtp (5b); 5-BuCBbtp (5c); 5-(R)CBbtp = 2-(2'-benzothienyl)-5-(2-R-ortho-carboran-1-yl)-pyridinato-C(2),N, R = Me and n-Bu; 4-BuCBbtp = 2-(2'-benzothienyl)-4-(2-n-Bu-ortho-carboran-1-yl)-pyridinato-C(2),N, acac = acetylacetonate) complexes supported by o-carborane substituted C(∧)N-chelating ligand were prepared, and the crystal structures of 5a and 5b were determined by X-ray diffraction. While 5a and 5c exhibit a deep red phosphorescence band centered at 644 nm, which is substantially red-shifted compared to that of unsubstituted (btp)2Ir(acac) (6) (λem = 612 nm), 5b is nonemissive in THF solution at room temperature. In contrast, all complexes are emissive at 77 K and in the solid state. Electrochemical and theoretical studies suggest that the carborane substitution leads to the lowering of both the HOMO and LUMO levels, but has higher impact on the LUMO stabilization than the HOMO, resulting in the reduction of the triplet excited state energy. In particular, the LUMO stabilization in the 4-substituted 5b is more contributed by carborane than that in the 5-substituted 5a. The solution-processed electroluminescent device incorporating 5a as an emitter displayed deep red phosphorescence (CIE coordinate: 0.693, 0.290) with moderate performance (max ηEQE = 3.8%) whereas the device incorporating 5b showed poor performance, as well as weak luminance.

Colorless and transparent copolyimide nanocomposites.

Copolyimides (Co-PIs) were synthesized from 2,2'-bis(trifluoromethyl) benzidine (TFB) and different ratios of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and pyromellitic dianhydride (PMDA). The Co-PI films were obtained from poly(amic acid) (PAA) by solution-casting through typical chemical and thermal imidizations. The thermal properties and optical transparency of the Co-PI films with various PMDA monomer contents were investigated. It was found that with increasing PMDA content, the thermal transition temperatures of the Co-PI films increased. Co-PI nanocomposites were prepared with various amounts of organically modified hectorite (STN) on a TFB:6FDA:PMDA = 1.0:0.9:0.1 mole ratio Co-PI hybrid film to examine the thermal properties, morphology, and optical transparency. The thermo-optical properties of the Co-PI hybrid films deteriorated with increasing clay content. However, the coefficient of thermal expansion (CTE) and oxygen barrier properties of the PI hybrid films improved with increasing clay content.

Heteroleptic tris-cyclometalated iridium(III) complexes supported by an o-carboranyl-pyridine ligand.

Heteroleptic tris-cyclometalated Ir(III) complexes supported by the o-carboranyl-pyridine (CBpy) as a novel C^N chelating ligand were synthesized and characterized. While the CBpy ligand contributes to the electronic stabilization of complexes, their photophysical properties are dominated by 2-arylpyridine ligands.

Synthesis and electron transporting properties of methanofullerene-o-carborane dyads in organic field-effect transistors.

A series of methanofullerene-o-carborane dyads (PCB-Ph-CB, PCB-Cn-CB, n = 1, 3, 6, 11) were synthesized via esterification of [6,6]-phenyl-C61-butyric acid (PCBA) with 2-alcohol functionalized o-carborane derivatives, 1-(4-n-BuC6H4)-2-R-1,2-closo-C2B10H10 (R = p-C6H4OH, (CH2)nOH, n = 1, 3, 6, 11). All the dyads are highly soluble in chlorinated and aromatic solvents under ambient conditions. UV-vis absorption and electrochemical reduction of the dyads exhibited features almost identical to each other, as well as to their parent PCBM, suggesting that the electronic properties of the dyads would be dominated by the methanofullerene moiety. Solution-processed field-effect transistors (FETs) incorporating the methanofullerene-o-carborane dyads as active layer materials were fabricated and tested. AFM images of all the thin films showed a homogeneous morphology with RMS values of 0.184-0.212 nm. The transport data are shown to be typical of n-channel FETs. Among the devices, the PCB-C1-CB FET showed the best performance, with an electron mobility of 1.72 × 10(-2) cm(2) V(-1) s(-1), which is similar to that of PCBM. While the device performances gradually decreased with increasing length of the alkyl linker, they are superior to that (6.83 × 10(-4) cm(2) V(-1) s(-1)) of the physical blend of o-carborane and PCBM.

Genotoxic evaluation of the biocomponents of the cricket, Gryllus bimaculatus, using three mutagenicity tests.

The mutagenic potential of the extracted components of Gryllus bimaculatus, a species of cricket, was evaluated using short-term genotoxicity tests including the Ames, chromosome aberration, and micronuclei tests. In a Salmonella typhimurium assay, G. bimaculatus extract did not produce any mutagenic response in the absence or presence of S9 mix with TA98, TA100, TA1535, and TA1537. Chromosome aberration testing showed that G. bimaculatus had no significant effect on Chinese hamster ovary (CHO) cells. In the mouse micronucleus test, no significant alteration in occurrence of micronucleated polychromatic erythrocytes was observed in ICR male mice intraperitoneally administered with G. bimaculatus extract at doses of 15, 150, or 1500 mg/kg. These results indicate that G. bimaculatus extract exerts no mutagenic effect in these in vitro and in vivo systems.

Ras transgene expression in TG-AC mice treated with benzo[a]pyrene.

Transgene expression and skin tumorigenicity were investigated in transgenic TG-AC mice carrying the v-Ha-ras after treatment with benzo[a]pyrene (BP). Animals treated with 40 microg BP (x2/week/mouse) showed 100% tumor response after 25 weeks, as did 40% of the mice treated with 20 microg BP but 10 microg BP did not produce a tumor response. In the case of animals treated with 40 microg BP for 25 weeks, most of the tumors were proven to be carcinomas (80%, 4 out of 5 mice), and all tumors were shown to be positive in terms of transgene expression detected by in situ hybridization. These data suggest that BP was tumorigenic in a dose-dependent manner in TG-AC mice and that TG-AC mice were dependent on transgene expression during BP carcinogenesis.