Thermally Activated Delayed Fluorescence with Nanosecond Emission Lifetimes and Minor Concentration Quenching: Achieving High-Performance Nondoped and Doped Blue OLEDs.

Simultaneously achieving a high photoluminescence quantum yield (PLQY), ultrashort exciton lifetime, and suppressed concentration quenching in thermally activated delayed fluorescence (TADF) materials is desirable yet challenging. Here, a novel acceptor-donor-acceptor type TADF emitter, namely, 2BO-sQA, wherein two oxygen-bridged triarylboron (BO) acceptors are arranged with cofacial alignment and positioned nearly orthogonal to the rigid dispirofluorene-quinolinoacridine (sQA) donor is reported. This molecular design enables the compound to achieve highly efficient (PLQYs up to 99%) and short-lived (nanosecond-scale) blue TADF with effectively suppressed concentration quenching in films. Consequently, the doped organic light-emitting diodes (OLEDs) base on 2BO-sQA achieve exceptional electroluminescence performance across a broad range of doping concentrations, maintaining maximum external quantum efficiencies (EQEs) at over 30% for doping concentrations ranging from 10 to 70 wt%. Remarkably, the nondoped blue OLED achieves a record-high maximum EQE of 26.6% with a small efficiency roll-off of 14.0% at 1000 candelas per square meter. By using 2BO-sQA as the sensitizer for the multiresonance TADF emitter ν-DABNA, TADF-sensitized fluorescence OLEDs achieve high-efficiency deep-blue emission. These results demonstrate the feasibility of this molecular design in developing TADF emitters with high efficiency, ultrashort exciton lifetime, and minimal concentration quenching.

Rational Design of Highly Efficient Orange-Red/Red Thermally Activated Delayed Fluorescence Emitters with Submicrosecond Emission Lifetimes.

The development of orange-red/red thermally activated delayed fluorescence (TADF) materials with both high emission efficiencies and short lifetimes is highly desirable for electroluminescence (EL) applications, but remains a formidable challenge owing to the strict molecular design principles. Herein, two new orange-red/red TADF emitters, namely AC-PCNCF3 and TAC-PCNCF3, composed of pyridine-3,5-dicarbonitrile-derived electron-acceptor (PCNCF3) and acridine electron-donors (AC/TAC) are developed. These emitters in doped films exhibit excellent photophysical properties, including high photoluminescence quantum yields of up to 0.91, tiny singlet-triplet energy gaps of 0.01 eV, and ultrashort TADF lifetimes of less than 1 µs. The TADF-organic light-emitting diodes employing the AC-PCNCF3 as emitter achieve orange-red and red EL with high external quantum efficiencies of up to 25.0% and nearly 20% at doping concentrations of 5 and 40 wt%, respectively, both accompanied by well-suppressed efficiency roll-offs. This work provides an efficient molecular design strategy for developing high-performance red TADF materials.

Realizing High-Efficiency Orange-Red Thermally Activated Delayed Fluorescence Materials through the Construction of Intramolecular Noncovalent Interactions.

The development of highly efficient orange and red thermally activated delayed fluorescence (TADF) materials for constructing full-color and white organic light-emitting diodes (OLEDs) remains insufficient because of the formidable challenges in molecular design, such as the severe radiationless decay and the intrinsic trade-off between the efficiencies of radiative decay and reverse intersystem crossing (RISC). Herein, we design two high-efficiency orange and orange-red TADF molecules by constructing intermolecular noncovalent interactions. This strategy could not only ensure high emission efficiency via suppression of the nonradiative relaxation and enhancement of the radiative transition but also create intermediate triplet excited states to ensure the RISC process. Both emitters exhibit typical TADF characteristics, with a fast radiative rate and a low nonradiative rate. Photoluminescence quantum yields (PLQYs) of the orange (TPA-PT) and orange-red (DMAC-PT) materials reach up to 94 and 87%, respectively. Benefiting from the excellent photophysical properties and stability, OLEDs based on these TADF emitters realize orange to orange-red electroluminescence with high external quantum efficiencies reaching 26.2%. The current study demonstrates that the introduction of intermolecular noncovalent interactions is a feasible strategy for designing highly efficient orange to red TADF materials.

Thermally Activated Delayed Fluorescence Amorphous Molecular Materials for High-Performance Organic Light-Emitting Diodes.

Small-molecule thermally activated delayed fluorescence (TADF) materials have been extensively developed to actualize efficient organic LEDs (OLEDs). However, organic small molecules generally compromise thin film quality and stability due to the tendency of crystallization, aggregation, and phase separation, which hence degrade the efficiency and long-term stability of the OLEDs. Here, for the first time, we exploit the unique molecular configuration of the bimesitylene scaffold to design two highly efficient TADF amorphous molecular materials with excellent thermal and morphological stabilities. The twisted and rigid bimesitylene scaffold thwarts regular molecular packing and crystallization, thereby guaranteeing homogeneous and stable amorphous thin films. Meanwhile, the highly twisted geometry of the bimesitylene scaffold efficiently breaks the molecular conjugation and thus conserves the high energies of the lowest locally excited triplet states (3LE) above the lowest charge transfer states (1CT and 3CT), leading to small singlet-triplet energy splitting and fast reverse intersystem crossing. These TADF emitters exhibit high photoluminescence quantum yields of 0.90 and 0.69 and short TADF lifetimes of 4.94 and 1.44 µs in doped films, based on which the greenish-blue and greenish-yellow OLEDs achieve external quantum efficiencies of 23.2 and 16.2%, respectively, with small efficiency roll-off rates and perfect color stability.

Hartmann reversal: obesity adversely impacts outcome.

BACKGROUND: Comprehensive analyses are lacking to identify predictors of postoperative complications in patients who undergo a Hartmann reversal. OBJECTIVE: The aim of this study is to identify predictive factors for morbidity after reversal. DESIGN: This study is a retrospective review of prospectively collected data. SETTINGS: The study was conducted at Cleveland Clinic Florida. PATIENTS: Consecutive patients from January 2004 to July 2011 who underwent reversal were included. MAIN OUTCOME MEASURES: Variables pertaining to Hartmann procedure and reversal were obtained for analyses in patients with and without postoperative complications. Univariate and multivariate analyses were performed. RESULTS: A total of 95 patients (mean age 61 years, 56% male) underwent reversal, with an overall morbidity of 46%. Patients with and without complications had similar demographics, comorbidities, diagnoses, and Hartmann procedure intraoperative findings. Patients with complications after reversal were more likely to have prophylactic ureteral stents (61% vs 41%, p < 0.05) and an open approach (91% vs 75%, p < 0.04). Complications were associated with longer hospital stay (8.8 vs 6.9 days,p < 0.006) and higher rates of reintervention (9% vs 0%, p < 0.03) and readmission (16% vs 2%, p < 0.02). Predictors of morbidity after reversal included BMI (29 vs 26 kg/m, p < 0.04), hospital stay for Hartmann procedure (15 vs 10 days, p < 0.03), and short distal stump (50% vs 31%, p < 0.05). BMI was the only independent predictor of morbidity (p < 0.04). Obesity was associated with significantly greater overall morbidity (64% vs 40%, p < 0.04), wound infections (56% vs 31%, p < 0.04), diverting ileostomy at reversal (24% vs 13%, p < 0.05), and time between procedures (399 vs 269 days, p < 0.02). LIMITATIONS: This study was limited by its retrospective design. CONCLUSIONS: Hartmann reversal is associated with significant morbidity; BMI independently predicts complications. Therefore, patients who are obese should be encouraged or even potentially required to lose weight before reversal.

Derivation and validation of a prediction rule for estimating advanced colorectal neoplasm risk in average-risk Chinese.

No prediction rule is currently available for advanced colorectal neoplasms, defined as invasive cancer, an adenoma of 10 mm or more, a villous adenoma, or an adenoma with high-grade dysplasia, in average-risk Chinese. In this study between 2006 and 2008, a total of 7,541 average-risk Chinese persons aged 40 years or older who had complete colonoscopy were included. The derivation and validation cohorts consisted of 5,229 and 2,312 persons, respectively. A prediction rule was developed from a logistic regression model and then internally and externally validated. The prediction rule comprised 8 variables (age, sex, smoking, diabetes mellitus, green vegetables, pickled food, fried food, and white meat), with scores ranging from 0 to 14. Among the participants with low-risk (≤3) or high-risk (>3) scores in the validation cohort, the risks of advanced neoplasms were 2.6% and 10.0% (P < 0.001), respectively. If colonoscopy was used only for persons with high risk, 80.3% of persons with advanced neoplasms would be detected while the number of colonoscopies would be reduced by 49.2%. The prediction rule had good discrimination (area under the receiver operating characteristic curve = 0.74, 95% confidence interval: 0.70, 0.78) and calibration (P = 0.77) and, thus, provides accurate risk stratification for advanced neoplasms in average-risk Chinese.