Design Approach of Lifetime Extending Thermally Activated Delayed Fluorescence Sensitizers for Highly Efficient Fluorescence Devices.

In this work, a design approach of three thermally activated delayed fluorescence (TADF) emitters to extend the device lifetime of the TADF sensitized fluorescent devices was studied. Three TADF materials, 5-{4,6-bis[4-(tert-butyl)phenyl]-1,3,5-triazin-2-yl}-2-(10,15-diphenyl-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazol-5-yl)benzonitrile (tTCNTruX), 4-[3-cyano-4-(10,15-diphenyl-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazol-5-yl)phenyl]-2,6-diphenylpyrimidine-5-carbonitrile (PCNTruX) and 4-(4-{10,15-bis[4-(tert-butyl)phenyl]-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazol-5-yl}-3-cyanophenyl)-2,6-diphenylpyrimidine-5-carbonitrile (PCNtTruX), were synthesized as sensitizers for TADF-sensitized fluorescent organic light-emitting diodes. The two tTCNTruX and PCNtTruX TADF emitters were designed to have Dexter energy transfer with blocking groups either in the donor or acceptor unit of the donor-acceptor-type TADF sensitizer. The TADF materials showed small singlet-triplet energy splitting and a high reverse intersystem crossing (RISC) rate for effective sensitization of the fluorescent emission of the fluorescent emitter. tTCNTruX- and PCNtTruX-sensitized fluorescent devices showed maximum external quantum efficiencies (EQEs) of 17.7 % and 11.5 % in the yellow and red devices, respectively, which were higher than those of TADF-sensitized devices with the corresponding TADF sensitizer without a blocking group. Moreover, the device lifetime was also extended by employing the tTCNTruX and PCNtTruX sensitizers. This work demonstrated that the tTCNTruX and PCNtTruX sensitizers are effective to improve the maximum EQE and device lifetime of TADF-sensitized fluorescent devices.

Effects of Substitution Position of Carbazole-Dibenzofuran Based High Triplet Energy Hosts to Device Stability of Blue Phosphorescent Organic Light-Emitting Diodes.

High triplet energy hosts were developed through the modification of the substitution position of carbazole units. Two carbazole-dibenzofuran-derived compounds, 9,9'-(dibenzo[b,d]furan-2,6-diyl)bis(9H-carbazole) (26CzDBF) and 4,6-di(9H-carbazol-9-yl)dibenzo[b,d]furan (46CzDBF), were synthesized for achieving high triplet energy hosts. In comparison with the reported hole transport type host, 2,8-di(9H-carbazol-9-yl)dibenzo[b,d]furan (28CzDBF), 26CzDBF and 46CzDBF maintained high triplet energy over 2.95 eV. The device performances of the hosts were evaluated with electron transport type host, 2-phenyl-4, 6-bis(3-(triphenylsilyl)phenyl)-1,3,5-triazine (mSiTrz), to comprise a mixed host system. The deep blue phosphorescent device of 26CzDBF:mSiTrz with [[5-(1,1-dimethylethyl)-3-phenyl-1H-imidazo[4,5-b]pyrazin-1-yl-2(3H)-ylidene]-1,2-phenylene]bis[[6-(1,1-dimethylethyl)-3-phenyl-1H-imidazo[4,5-b]pyrazin-1-yl-2(3H)-ylidene]-1,2-phenylene]iridium (Ir(cb)3) dopant exhibited high external quantum efficiency of 22.9% with a color coordinate of (0.14, 0.16) and device lifetime of 1400 h at 100 cd m-2. The device lifetime was extended by 75% compared to the device lifetime of 28CzDBF:mSiTrz (800 h). These results demonstrated that the asymmetric and symmetric substitution of carbazole can make differences in the device performance of the carbazole- and dibenzofuran- derived hosts.

Narrowband and Pure Violet Organic Emitter with a Full Width at Half Maximum of 14 nm and y Color Coordinate of Below 0.02.

Violet organic light-emitting diodes (OLEDs) with a very narrow emission spectrum with a full width at half maximum of 14 nm and y color coordinate of 0.02 are developed using a indolo[3,2,1-jk]carbazole-derived pure violet emitter. The violet emitter, 2,5,13,16-tetra-tert-butylindolo[3,2,1-jk]-indolo[1',2',3':1,7]indolo[2,3-b]carbazole (tDIDCz), is designed to have a very rigid molecular structure driven by the multiresonance-type core structure through the alternating carbon and nitrogen atoms. The violet emitter is decorated with t-butyl groups to prevent intermolecular aggregation and packing, which allow pure violet emission without excimer emission. The violet OLEDs derived from the tDIDCz emitter show a violet color coordinate of (0.164, 0.018) with a narrow emission spectrum and a full width at half maximum of 14 nm (105 meV). The external quantum efficiency of the pure violet OLEDs is 3.3%. This is the first work reporting pure violet emission without any ultraviolet emission below 380 nm and blue emission above 450 nm by showing a very narrow emission spectrum.

Asymmetric Decoration of a meta-Linked Bitriazine-Based Host for Highly Efficient and Stable Blue Phosphorescent Organic Light-Emitting Diodes.

High triplet energy hosts for blue phosphorescent organic light-emitting diodes were developed by decorating a meta-linked bitriazine core with carbazole and tetraphenylsilyl functional groups. A symmetric host with two carbazole units as the two triazine units of the core and an asymmetric host with one carbazole unit and one tetraphenylsilyl unit as the two triazine units were prepared. The triplet energy of these two hosts was 2.97 eV, suitable for triplet exciton harvesting of blue phosphors. Comparing the two host designs, the asymmetric decoration of the two triazine units with carbazole and tetraphenylsilyl units was superior to the symmetric decoration of the two triazine units with two carbazoles in terms of high external quantum efficiency (EQE) and long-term device stability. A high EQE of 19.7% and a long device lifetime of 2093.6 h at 100 cd m-2 were achieved using the asymmetrical host.

Rational Molecular Design of Azaacene-Based Narrowband Green-Emitting Fluorophores: Modulation of Spectral Bandwidth and Vibronic Transitions.

A series of green-emitting fluorophores based on a tetra-azaacene core is synthesized by introducing nitrile substituents at different positions. Their molecular structure-optical property relationship [i.e., vibronic transitions in photoluminescence (PL) and electroluminescence (EL) spectra] is investigated to obtain a sharp emission where the vibronic peak ν0-0 should be intensified by suppressing ν0-n (n = 1, 2, 3...) transitions. The intensity ratios (I0-1/I0-0) of the ν0-1 and ν0-0 vibronic transitions in the PL spectra of DBBNP, DBBNP2CN1, and DBBNP2CN2 in hexane are 1.13, 0.80, and 0.67, respectively. Theoretical calculations explain that the CN substitution at positions 8 and 13 in DBBNP2CN2 induces a uniform charge distribution and reduces the Huang-Rhys factors (HRFs) of the vibrational normal modes coupled to the electronic transition. The organic light-emitting diode (OLED) fabricated with DBBNP2CN2 shows a narrower green EL emission at 518 nm with a smaller bandwidth (50 nm) than those of devices adopting DBBNP or DBBNP2CN1. The careful modification of the molecular structures and positions of substituents enables us to reduce the HRFs of vibrations to achieve a narrow emission bandwidth with decreased I0-1/I0-0, which suggests a design strategy to develop narrowband organic fluorophores to improve the color purity for wide-gamut OLED displays.

Purely Spin-Vibronic Coupling Assisted Triplet to Singlet Up-Conversion for Real Deep Blue Organic Light-Emitting Diodes with Over 20% Efficiency and y Color Coordinate of 0.05.

Finding narrow-band, ultrapure blue thermally activated delayed fluorescence (TADF) materials is extremely important for developing highly efficient organic light-emitting diodes (OLEDs). Here, spin-vibronic coupling (SVC)-assisted ultrapure blue emitters obtained by joining two carbazole-derived moieties at a para position of a phenyl unit and performing substitutions using several blocking groups are presented. Despite a relatively large singlet-triplet gap (∆EST ) of >0.2 eV, efficient triplet-to-singlet crossover can be realized, with assistance from resonant SVC. To enhance the spin crossover, electronic energy levels are fine-tuned, thereby causing ∆EST to be in resonance with a triplet-triplet gap (∆ETT ). A sizable population transfer between spin multiplicities (>103 s-1 ) is achieved, and this result agrees well with theoretical predictions. An OLED fabricated using a multiple-resonance-type SVC-TADF emitter with CIE color coordinates of (0.15, 0.05) exhibits ultrapure blue emissions, with a narrow full-width-at-half-maximum of 21 nm and a high external quantum efficiency of 23.1%.

Rational Molecular Design of Highly Efficient Yellow-Red Thermally Activated Delayed Fluorescent Emitters: A Combined Effect of Auxiliary Fluorine and Rigidified Acceptor Unit.

Molecular design strategies are crucial to develop highly efficient and long-wavelength thermally activated delayed fluorescent (TADF) emitters because the inherent limitation of the energy gap law degrades the efficiency of the red or orange TADF emitters. To resolve the low efficiency issue, we designed and synthesized two TADF emitters, 4,4'-(6-(9,9-dimethylacridin-10(9H)-yl)-7-fluoroquinoxaline-2,3-diyl)dibenzonitrile (FDQCNAc) and 11-(9,9-dimethylacridin-10(9H)-yl)-12-fluorodibenzo[a,c]phenazine-3,6-dicarbonitrile (FBPCNAc), by utilizing fluorine and peripheral cyano-substituted quinoxaline and phenazine acceptors of 4,4'-(6-fluoroquinoxaline-2,3-diyl)dibenzonitrile (FDQCN) and 11-fluorodibenzo[a,c]phenazine-3,6-dicarbonitrile (FBPCN), respectively. A fluorine atom at the ortho position of the acridine donor acts as an auxiliary acceptor to minimize the singlet-triplet energy gap (ΔEST) below 0.1 eV and promotes the reverse intersystem crossing (RISC) process. Organic light-emitting diodes (OLEDs) fabricated with FDQCNAc and FBPCNAc emitters demonstrated high external quantum efficiencies (EQEs) of 27.6 and 23.8% in the yellow-red TADF OLEDs, respectively. In particular, the combination of the F auxiliary acceptor unit and the rigidified FBPCN acceptor unit enabled red-shifted emission by about 58 nm without much sacrifice of the EQE in the red region.

C1-, C2-, and C3-Modified Carbazole Derivatives as Promising Host Materials for Phosphorescent Organic Light-Emitting Diodes.

Herein we unveiled the synthetic approach to C1-, C2-, and C3-modified carbazoles for the first time and designed high-triplet-energy bipolar host materials for green phosphorescent organic light-emitting devices. The compounds revealed excellent performance with a maximum external quantum efficiency as high as 23.6% and extremely low-efficiency roll-off of 2.1% at high brightness of 1000 cd/m2.

PROSPECT-PSPP: an automatic computational pipeline for protein structure prediction.

Knowledge of the detailed structure of a protein is crucial to our understanding of the biological functions of that protein. The gap between the number of solved protein structures and the number of protein sequences continues to widen rapidly in the post-genomics era due to long and expensive processes for solving structures experimentally. Computational prediction of structures from amino acid sequence has come to play a key role in narrowing the gap and has been successful in providing useful information for the biological research community. We have developed a prediction pipeline, PROSPECT-PSPP, an integration of multiple computational tools, for fully automated protein structure prediction. The pipeline consists of tools for (i) preprocessing of protein sequences, which includes signal peptide prediction, protein type prediction (membrane or soluble) and protein domain partition, (ii) secondary structure prediction, (iii) fold recognition and (iv) atomic structural model generation. The centerpiece of the pipeline is our threading-based program PROSPECT. The pipeline is implemented using SOAP (Simple Object Access Protocol), which makes it easier to share our tools and resources. The pipeline has an easy-to-use user interface and is implemented on a 64-node dual processor Linux cluster. It can be used for genome-scale protein structure prediction. The pipeline is accessible at http://csbl.bmb.uga.edu/protein_pipeline.

Unexpected stent thrombus after minimally invasive direct coronary artery bypass in hybrid re-vascularisation.

The progress in anti-platelet therapy and percutaneous coronary intervention led to reconfigure indications of hybrid re-vascularisation. However, there are still some controversies over indication, timing and patient management during the procedure. The case discussed here is a patient who was diagnosed with myocardial infarction and treated with hybrid re-vascularisation. The patient underwent stent insertion followed by bypass surgery. After the hybrid procedure, the patient was stable but eventually died on the 12th day after the surgery owing to unexpected stent thrombosis. We discuss the current controversy over hybrid re-vascularisation, variables that can affect the outcome and the requirement for establishing accurate logistics based on our case.

Effects of additional pleurodesis with dextrose and talc-dextrose solution after video assisted thoracoscopic procedures for primary spontaneous pneumothorax.

Recurrence after thoracoscopic surgery for primary spontaneous pneumothorax is a lingering problem, and many intraoperative methods to induce pleural symphysis have been introduced. We analyzed the effects of chemical pleurodesis during thoracoscopic procedures. Between August 2003 and July 2005, 141 patients among indicated surgical treatment for primary spontaneous pneumothorax in two hospitals of our institution allowed this prospective study. The patients were randomly assigned to 3 groups: thoracoscopic procedure only (group A, n=50), thoracoscopic procedure and pleurodesis with dextrose solution (group B, n=49), and thoracoscopic procedure and pleurodesis with talc-dextrose mixed solution (group C, n=42). There was no significant difference in demographic data among the three groups. The two groups that underwent intraoperative pleurodesis had significantly longer postoperative hospital stays (A/B/C: 2.50+/-1.85/4.49+/-2.10/6.00+/-2.58 days; p=0.001) and a higher incidence of postoperative fever (A/B/C: 10.0/22.45/52.38%; chi(2)= 21.598, p=0.00). No significant differences were found for recurrence rates or the number of postoperative days until chest tube removal. Therefore, the results of our study indicate that intraoperative chemical pleurodesis gives no additional advantage to surgery alone in deterring recurrence for patients with primary spontaneous pneumothorax. Thus, the use of such scarifying agents in the operating room must be reconsidered.

Mechanism of bar displacement and corresponding bar fixation techniques in minimally invasive repair of pectus excavatum.

PURPOSE: Bar displacement is a major complication in repair of pectus excavatum with the Nuss technique. Mechanisms of bar displacement have been elucidated by case-by-case analysis, and specific bar fixation techniques have been developed to deal with each mechanism. The efficacy of our bar fixation techniques is appraised. METHODS: Data from 725 consecutive patients between 1999 and 2006 who were repaired with our modifications to the Nuss procedure were retrospectively analyzed. RESULTS: The mechanism of bar displacement consisted of one or a combination of the following types: type 1, "bar flipping"--rotation of the bar along the axis of hinge; type 2, "lateral sliding"--horizontal slipping of the bar to one side in asymmetric pectus excavatum; and type 3, "hinge-point disruption"--a dorsal shift of the bar owing to tearing of the supporting intercostal musculature. Specific bar fixation techniques have been tailored to compensate for potential mechanisms of bar displacement according to pectus morphology: multipoint pericostal bar fixation (MPF) (n = 496) for type 1 displacement; incorporation of a stabilizer on the depressed side (n = 169) for type 2 displacement; and hinge point reinforcement and the crane technique (n = 122) for type 3 displacement. The bar displacement rate was decreased with our mechanism-based approach (4.6% before MPF vs 1.8% after MPF, P = .045). In addition, the major complication rates (6.8% before MPF vs 2.0% after MPF, P = .001) and reoperation rates (5.5% before MPF vs 1.6% after MPF, P = .019) decreased. CONCLUSIONS: Mechanism-based bar fixation techniques, especially multipoint pericostal wire fixation, seems to be effective in preventing bar displacement following pectus excavatum repair.

Needlescopic lung biopsy for interstitial lung disease and indeterminate pulmonary nodules: a report on 65 cases.

BACKGROUND: We evaluated the feasibility and accuracy of a needlescopic procedure for lung biopsies in patients with interstitial lung disease or indeterminate pulmonary nodules. METHODS: Sixty-five patients (36 women; mean age, 51.3 +/- 15.6; range, 13 to 76 years) underwent a needlescopic procedure to obtain lung biopsy specimens. Forty had indeterminate pulmonary nodules, and 25 had interstitial lung disease. A 2-mm needlescope and a 2-mm MiniSite Endo Grasp (Covidien, Norwalk, CT) were inserted at the sixth intercostal space along the middle and the posterior axillary line, respectively. Biopsy specimens were obtained using endostaplers. RESULTS: The average number of biopsy specimens was 1.7 +/- 0.6 (range, 1 to 4). For 9 patients, a frozen specimen was sent twice to pathology. Complete resection was continued after intraoperative pathology confirmation in 13 patients (lobectomy, 7; segmentectomy, 3; mass removal, 1; metastasectomy, 2). The volume of lung tissue was 8.7 +/- 11.8 cm3 (range, 0.15 to 55.44 cm3). The operation time was 58.7 +/- 37.5 minutes (range, 15 to 160 minutes). The final pathologic results were confirmed in all patients. No thoracoscopic procedure was converted to an open thoracotomy. Three patients (4.3%) had prolonged air leakage (> 5 days), and the chest tube remained in the pleural space for 2.3 +/- 2.4 days (range, 1 to 8 days). CONCLUSIONS: Needlescopic operation for lung biopsies in patients with interstitial lung disease and indeterminate pulmonary nodules is a minimally invasive procedure that is safe and effective for obtaining a diagnosis in selected patients.