Towards Efficient Blue DelayedFluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Constructing blue thermally activated delayedfluorescence materials for high-performance organic light-emitting diodes(OLEDs)remains challenging due to the intrinsically strong intramolecular charge transfer nature of the nearly orthogonal connection of electron donor(D)and acceptor(A),which results in long-wavelength emission.Herein,an effective delayed-fluorescence design strategy of modulating D–A torsion angles is proposed and efficient sky-blue,pure-blue,and deep-blue delayed-fluorescence molecules consisting of a xanthenone acceptor and carbazole-based donors are created by decreasing the torsion angles.They exhibit strong delayed fluorescence with high photoluminescence quantum yields of 85–94%in doped films,and their delayed-fluorescence lifetimes are elongated from 1.0 to 27.6μs as the torsion angles decrease.These molecules can function as excellent emitters in OLEDs,providing efficient electroluminescence peaking at 442 nm(CIEx,y=0.15,0.08),462 nm(CIEx,y=0.15,0.18),and 482 nm(CIEx,y=0.17,0.30)with state-of-the-art external quantum efficiencies of up to 22.2%,33.7%,and 32.1%,respectively,demonstrating the proposed molecular design for efficient blue delayed-fluorescence molecules is successful and promising.

Highly precise micro torsion angle detection by fringe array

Pringe array is proposed as the cooperated target in the precise torsion angle detection. The target fringe array image is generated according to the structure of the optical system, and the torsion angle detection algorithm is analyzed in response to the gray distribution of the image. The factors affecting the detection precision of the fringe torsion angle are analyzed theoretically and numerically. It indicates that the detection precision of the torsion angle is 1 angular second or even less, carefully selecting the detector array. Significantly, experiments are performed to demonstrate the precision and the results match well with the simulations.

Simulation of Vertical Solar Power Plants with Different Turbine Blades

The performances of turbine blades have a significant impact on the energy conversion efficiency of vertical solar power plants.In the present study,such a relationship is assessed by considering two kinds of airfoil blades,designed by using the Wilson theory.In particular,numerical simulations are conducted using the SST K−ω model and assuming a wind speed of 3–6 m/s and seven or eight blades.The two airfoils are the NACA63121(with a larger chord length)and the AMES63212;It is shown that the torsion angle of the former is smaller,and its wind drag ratio is larger;furthermore,the resistance is increased by about 66.3%on average.Within the scope of the study,the results show that the NACA63212 airfoil is better than the AMES63212 airfoil in terms of power,with an average improvement of about 2.8%.The simulation results have a certain guiding significance for selecting turbine blade airfoils and improving turbine efficiency.

CO2 Capture at Room Temperature and Ambient Pressure: Isomer Effect in Room Temperature Ionic Liquid/Propanol Solutions

A CO2 capture system without supercritical CO2 was optimized for mixtures of hydrophobic room temperature ionic liquids (RTILs) and propanol. We tested RTILs using bis(trifluoromethanesulfonyl)imide, TFSI-, anion and four quaternary ammonium cations, two quaternary phosphonium cations, and one imidazolium cation. The addition of 2-propanol into the RTILs clearly promoted the capture of normal CO2(nCO2) at ambient temperature and pressure. When combined with 2-propanol, the most efficient RTILs for nCO2 capture were N-butyl-N,N,N-trimethylammonium TFSI-. This enhancement of nCO2 capture was not observed in RTIL mixtures with 1-propanol or in propanol mixtures containing other phosphonium- and imidazolium-based RTILs. The torsion angle of TFSI-, which was calculated using density functional theory, is thought to be related to high nCO2 capture efficiently.

Hybridized Local and Charge-Transfer Excited-State Fluorophores through the Regulation of the Donor-Acceptor Torsional Angle for Highly Efficient Organic Light-Emitting Diodes

Hybridized local and charge-transfer(HLCT)excitedstate fluorophores,which enable full exciton utilization through a reverse intersystem crossing fromhigh-lying triplet states to singlet state,have attracted increasing attention toward organic light-emitting diodes(OLEDs)application.Herein,we report three D-π-A-π-D-type isomers o-2CzBT,m-2CzBT,and p-2CzBT by adjusting the donor(D)units from ortho-,meta-,to para-substituted positions with the acceptor(A)core unit,respectively.The HLCT properties of the three compounds are evidently confirmed by theoretical calculations,solvatochromic behaviors,and transient decay lifetimes analyses.As the substituted position changes from the ortho-,meta-,and para-positions,the reduced steric hindrance brings about decreased torsional angle between D and A moieties,resulting in increased oscillator strength.Accordingly,the parasubstituted p-2CzBT is endowed with a more locally excited component that accounts for faster radiative decay,leading to a higher fluorescent efficiency than that of o-2CzBT and m-2CzBT.As expected,p-2CzBT enables its nondoped and doped OLEDs with higher external quantum efficiencies(EQEs)of 12.3% and 15.0%,respectively,which are among the state-ofthe-art efficiencies of HLCT-based OLEDs.Moreover,o-2CzBT and m-2CzBT are also utilized as host materials for high-performance OLEDs,thus extending the application of HLCT materials.

Torsional behavior of triangular web profile （TRIWP） steel section by experimental study

A triangular web profile （TriWP） is a modified section where the flanges are connected to a web plate of triangular profile. This study examined the torsional behavior of TriWP steel sections and compared to that of the fiat web （FW） steel sections. Three types of specimen sizes were used： 180 mmx 75 mm × 5 mm× 2 mm, 200 mm × 100 mm× 8 mm ×6 mm, and 200 mm× 100 mm × 6 mm× 5 mm. All the specimens were loaded vertically until the maximum load was achieved and then the load was released. For both types of specimens, it was observed that the torsional rotation for bigger size [200 mm× 100 mm× 8 mm × 6 mm] were smaller than that of smaller size [ 180 mm × 75 mm×5 mm× 2 mm] of the specimens. At the maximum torsional loading, the experimental result was compared to the theoretical calculation. The comparison showed that the percentage difference ranged from 1.10% to 16.80%. From the graph of torsional load versus rotational angle, the torsional rotation for all TriWP steel sections were smaller than that of the FW steel section under the same torsional loading i.e., 0.2 kNm and 1 kNm. The range between FW and TriWP were 3.74 to 71.83 at 0.2 kNm while 14.5 to 75.1 at 1.0 kNm. The findings were shown that the TriWP steel sections had better resistance against torsion in comparison to FW steel section.