Delayed Luminescence in 2-Methyl-5-(penta(9-carbazolyl)phenyl)-1,3,4-oxadiazole Derivatives.

2,5-Diphenyl-1,3,4-oxadiazole has been widely used as an acceptor portion of donor-acceptor fluorophores that exhibit thermally activated delayed fluorescence (TADF), but analogous 2-alkyl-5-phenyl-1,3,4-oxadiazoles have been much less widely investigated. Here the properties of carbazole-substituted 2-methyl-5-phenyl-1,3,4-oxadiazoles are compared to those of their 2,5-diphenyl analogues. The fluorescence of each of the former compounds is blue-shifted by ca. 50-100 meV relative to that in the latter, while similar estimated values of the singlet-triplet energy separation (ΔEST) are maintained. In particular, 2-methyl-5-(penta(9-carbazolyl)phenyl)-1,3,4-oxadiazole and 2-methyl-5-(penta(3,6-di-tert-butyl-9-carbazolyl)phenyl)-1,3,4-oxadiazole exhibit solution fluorescence maxima of 466 and 485 nm and estimated ΔEST values of 0.12 and 0.03 eV, respectively. In both cases the reverse intersystem crossing (RISC) rates inferred from their solution fluorescence behavior are over twice those of the corresponding 2-phenyl derivatives. Organic light-emitting diodes (OLEDs) in which the 2-methyl derivatives are used as emitters yield external quantum efficiency (EQE) values of up to 23%. OLEDs with 2-methyl-5-(penta(9-carbazolyl)phenyl)-1,3,4-oxadiazole and 2-methyl-5-(penta(3,6-di-tert-butyl-9-carbazolyl)phenyl)-1,3,4-oxadiazole emitters show reduced efficiency rolloff at high current densities relative to their 2-phenyl counterparts, the latter exhibiting an EQE of 16% at 1000 cd m-2.

Mapping the effects of drought on child stunting.

As climate change continues, it is expected to have increasingly adverse impacts on child nutrition outcomes, and these impacts will be moderated by a variety of governmental, economic, infrastructural, and environmental factors. To date, attempts to map the vulnerability of food systems to climate change and drought have focused on mapping these factors but have not incorporated observations of historic climate shocks and nutrition outcomes. We significantly improve on these approaches by using over 580,000 observations of children from 53 countries to examine how precipitation extremes since 1990 have affected nutrition outcomes. We show that precipitation extremes and drought in particular are associated with worse child nutrition. We further show that the effects of drought on child undernutrition are mitigated or amplified by a variety of factors that affect both the adaptive capacity and sensitivity of local food systems with respect to shocks. Finally, we estimate a model drawing on historical observations of drought, geographic conditions, and nutrition outcomes to make a global map of where child stunting would be expected to increase under drought based on current conditions. As climate change makes drought more commonplace and more severe, these results will aid policymakers by highlighting which areas are most vulnerable as well as which factors contribute the most to creating resilient food systems.

Humidity Sensing through Reversible Isomerization of a Covalent Organic Framework.

Here we report that a covalent organic framework (COF), which contains 2,5-di(imine)-substituted 1,4-dihydroxybenzene (diiminol) moieties, undergoes color changes in the presence of solvents or solvent vapor that are rapid, passive, reversible, and easily detectable by the naked eye. A new visible absorption band appears in the presence of polar solvents, especially water, suggesting reversible conversion to another species. This reversibility is attributed to the ability of the diiminol to rapidly tautomerize to an iminol/cis-ketoenamine and its inability to doubly tautomerize to a diketoenamine. Density functional theory (DFT) calculations suggest similar energies for the two tautomers in the presence of water, but the diiminol is much more stable in its absence. Time-dependent DFT calculations confirm that the iminol/cis-ketoenamine absorbs at longer wavelength than the diiminol and indicate that this absorption has significant charge-transfer character. A colorimetric humidity sensing device constructed from an oriented thin film of the COF responded quickly to water vapor and was stable for months. These results suggest that tautomerization-induced electronic structure changes can be exploited in COF platforms to give rapid, reversible sensing in systems that exhibit long-term stability.

Facile Incorporation of Pd(PPh3)2Hal Substituents into Polymethines, Merocyanines, and Perylene Diimides as a Means of Suppressing Intermolecular Interactions.

Compounds with polarizable π systems that are susceptible to attack with nucleophiles at C-Hal (Hal = Cl, Br) bonds react with Pd(PPh3)4 to yield net oxidative addition. X-ray structures show that the resulting Pd(PPh3)2Hal groups greatly reduce intermolecular π-π interactions. The Pd-functionalized dyes generally exhibit solution-like absorption spectra in films, whereas their Hal analogues exhibit features attributable to aggregation.

Prognosis of Acute Low-Tone Hearing Loss Without Vertigo: A Scoping Review.

OBJECTIVE: Despite its relatively high prevalence, our understanding of the natural clinical course of acute low-tone hearing loss (ALHL) without vertigo remains incomplete. The purpose of this study is to summarize the findings of studies that evaluated recovery from hearing loss (HL), recurrence and/or fluctuation of HL, and progression to Meniere's Disease (MD) of patients presenting with ALHL without vertigo. METHODS: A scoping review of the English literature was performed. On May 14, 2020 and July 6, 2022, MEDLINE, Embase, and Scopus were searched to identify articles related to the prognosis of ALHL. To be included, articles had to present outcomes that were clearly distinguishable for patients with ALHL without vertigo. Two reviewers evaluated articles for inclusion and extracted data. Disagreements were adjudicated by a third reviewer. RESULTS: Forty-one studies were included. There was extensive heterogeneity between studies in regard to defining ALHL, treatment methods, and time of follow-up. Most of the cohorts (39 out of 40) reported partial or complete recovery of hearing in the majority (>50%) of patients, although reports of recurrence were relatively common. Progression to MD was infrequently reported. Shorter time from onset of symptoms to treatment predicted better hearing outcomes in 6 of 8 studies. CONCLUSION: The literature suggests that although the majority of patients with ALHL experience hearing improvement, recurrence and/or fluctuation are common, and progression to MD occurs in a minority of patients. Additional trials utilizing standardized inclusion and outcome criteria are needed to determine the ideal treatment for ALHL. LEVEL OF EVIDENCE: NA Laryngoscope, 133:2457-2469, 2023.

Determining the source of unusual xenon isotopes in samples.

Three unusual radioactive isotopes of xenon-125Xe, 127Xe, and 129mXe-have been observed during testing of a new generation radioxenon measurement system at the manufacturing facility in Knoxville, Tennessee. These are possibly the first detections of these isotopes in environmental samples collected by automated radioxenon systems. Unfortunately, the new isotopes detected by the Xenon International sampler can interfere with quantification of the radioactive xenon isotopes used to monitor for nuclear explosions. Xenon International sampling data collected during February through September 2020 were combined with an atmospheric transport model to identify the possible release location. A source-location analyses using sample counts dominated by 125Xe strongly supports the conclusion that the release point is near (within 20 km) the sampler location. Wind patterns are not consistent with releases coming from more distant nuclear power plants. The High Flux Isotope Reactor (HFIR) and the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory are located in the region of most likely source locations. The source-location analysis cannot rule out either facility as a release location, and some of the samples may contain a combination of releases from both facilities. The source-location results using 125Xe are not unexpected because Klingberg et al. (2013) previously published the production rate of radioactive xenon isotopes from neutron activation of stable xenon in the air at the HFIR. Up to 1012 Bq of 125Xe could be produced per operational day and other xenon isotopes would be produced in lesser quantities.

Reducing the risk of cerebrospinal fluid rhinorrhea following translabyrinthine surgery of the posterior fossa.

OBJECTIVE: To describe the procedure and results of an adapted closure and reconstruction technique for translabyrinthine surgery that focuses on identifying and managing potential pathways for CSF egress to the middle ear and Eustachian tube. METHODS: Retrospective review of a cohort of translabyrinthine acoustic neuroma cases that were reconstructed using this technique. RESULTS: In addition to meticulous packing of potential conduits using soft tissue, hydroxyapatite cement is used to seal opened air cell tracts prior to obliteration of the mastoid defect using adipose tissue. Early results of a small patient cohort using this technique are encouraging and there were no wound infections. There was a single case of CSF rhinorrhea associated with incomplete sealing of opened petrous apex cells, with no recurrence after appropriate implementation of the described protocol during revision surgery. CONCLUSION: Proactive management of potential conduits of CSF egress including opened air cell tracts has a high likelihood of reducing rates of rhinorrhea and need for revision surgery after the translabyrinthine approach to the posterior fossa.

Electron spin resonance resolves intermediate triplet states in delayed fluorescence.

Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic states and associated small singlet-triplet energy separations; triplets can then be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient electron spin resonance studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between local excitation and charge-transfer triplet states. The observation of distinct triplet signals, unusual in transient electron spin resonance, suggests that multiple triplet states mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between local excitation and charge-transfer triplet states decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states.

Associations of Vestibular Tests With Penn Acoustic Neuroma Quality of Life Scores After Resection of Vestibular Schwannoma.

OBJECTIVE: Determine associations between preoperative caloric testing and video head impulse testing (vHIT) with baseline and postoperative Penn Acoustic Neuroma Quality of Life (PANQOL) scores following resection of vestibular schwannoma (VS). STUDY DESIGN: Retrospective case series. SETTING: Two tertiary referral hospitals. PATIENTS: Adult patients with unilateral VS, preoperative calorics, vHIT, and dizziness handicap inventory (DHI) score. INTERVENTIONS: Surgical resection of VS and postoperative surveys. MAIN OUTCOME MEASURES: PANQOL scores. RESULTS: Forty-three patients were included (58.1% women) with a median age of 54 years (range, 28-82). Mean tumor size was 14.8 mm (σ=8.6), and 28 (65.1%) were right-sided. Average preoperative vHIT gain was 0.7 (σ = 0.3). Covert and overt saccades were present in 8 (25%) and 14 (42.4%) patients, respectively. Average preoperative unilateral weakness was 47% (σ = 33.2). Translabyrinthine approach was performed in 26 (60.5%) patients. No significant difference of PANQOL scores was noted at baseline or over time between patients with normal (>0.8) or abnormal (<0.8) gain. Patients with more unilateral weakness (>50%) had significantly higher baseline PANQOL scores compared with those with < 25% or 25 to 50% (p = 0.02), but had significant improvement in scores over time (p = 0.01). Higher preoperative DHI preoperatively was significantly associated with worse PANQOL scores at all timepoints (ß=0.57, p = 0.0064). No differences in PANQOL scores amongst surgical approaches were observed. CONCLUSION: Preoperative vestibular testing with vHIT, calorics, DHI, and baseline PANQOL surveys may allow for patient counseling regarding postoperative quality of life over time.

Host-Free Yellow-Green Organic Light-Emitting Diodes with External Quantum Efficiency over 20% Based on a Compound Exhibiting Thermally Activated Delayed Fluorescence.

Thermally activated delayed fluorescent (TADF) materials are advantageous as emitters in organic light-emitting diodes (OLEDs) due to their ability to utilize all excited states formed by charge recombination for light emission, potentially leading to 100% internal quantum efficiency. As in conventional fluorescent or phosphorescent OLEDs, TADF emitters are commonly doped at a relatively low concentration in a host matrix. However, increasing evidence suggests that balanced ambipolar transport properties and small aggregation-induced fluorescence quenching allow TADF emitters to be used alone in so-called host-free OLEDs. Here, we report host-free OLEDs in which the emissive layers (EMLs) consist solely of a yellow-green-emitting TADF compound, 5,5'-(2,3,5,6-tetra(carbazol-9-yl)-1,4-phenylene)bis(2-(4-( tert-butyl)phenyl)-1,3,4-oxadiazole), TCZPBOX. Devices with this host-free EML yield a maximum external quantum efficiency (EQE) of 21%, current efficacy (CE) of 73 cd/A, and power efficacy (PE) of 79 lm/W at a luminance of 10 cd/m2. At a high luminance of 10,000 cd/m2, a high EQE of 13% is maintained. A maximum luminance of 120,000 cd/m2 is reached at an applied voltage of 9.8 V. When TCZPBOX was doped in the host 2,6-di(carbazol-9-yl)-pyridine (PYD2) at 40 wt %, the device yielded a maximum EQE of 28%, CE of 94 cd/A, and PE of 100 lm/W at 10 cd/m2.

Control of Singlet Emission Energy in a Diphenyloxadiazole Containing Fluorophore Leading To Thermally Activated Delayed Fluorescence.

2-(4-(9,9-Dimethylacridin-10(9H)-yl)phenyl)-5-phenyl-1,3,4-oxadiazole has an energy difference between the lowest excited singlet and triplet states (ΔE ST) of ca. 0.24 eV. Introduction of two electronegative fluorine atoms onto the acceptor portion of the molecule to give 2-(4-(9,9-dimethylacridin-10(9H)-yl)-3,5-difluorophenyl)-5-phenyl-1,3,4-oxadiazole lowers the energy of the singlet emission with a negligible effect on the corresponding triplet energy, leading to a donor-acceptor compound with decreased ΔE ST of ca. 0.13 eV that displays thermally activated delayed fluorescence. Organic light-emitting diodes fabricated using the latter compound display high EQEmax of 21.9% at a luminance of 10 cd/m2 and sky-blue emission, however, they suffer from a large efficiency roll-off at increased luminance.