Improving Efficiency of Red Thermally Activated Delayed Fluorescence Emitter by Introducing Quasi-Degenerate Orbital Distribution

Red thermally activated delayed fluorescence(TADF)emitters are essential for the development of organic light-emitting diodes(OLEDs).To better understand and develop red TADF emitters,herein,the effect of quasi-degenerate orbital distribution was inves-tigated on their performance.Two red TADF emitters 10,10'-(11,12-difluorodibenzo[a,c]phenazine-3,6-diyl)bis(10H-phenoxazine)(DPXZ-BPF)and 10,10',10"-(12-fluorodibenzo[a,c]phenazine-3,6,11-triyl)tris(10H-phenoxazine)(TPXZ-BPF)were constructed by combining two or three phenoxazine(PXZ)donor units with a rigid coplanar acceptor core.As expected,a couple of PXZ units can induce quasi-degenerate orbital distribution by virtue of the high steric hindrance between each donor unit and acceptor core,which enables multiple excited states engaged in the reverse intersystem crossing(RISC)process.Consequently,DPXZ-BPF and TPXZ-BPF exhibit fast RISC rates(k_(RISCs))of 1.07×10^(6) s^(-1) and 1.29×10^(6) s^(-1) and high PLQYs of 74.6% and 81.1%,respectively.And the higher kRISC and PLQY of TPXZ-BPF are mainly attributed to the additional quasi-degenerate orbitals,which further enhance the tri-plet RISC process and the singlet radiative process.As a result,TPXZ-BPF-based OLEDs achieved improved efficiencies with a red-shifted emission compared with DPXZ-BPF-based OLEDs.These results demonstrated the tremendous potential of introducing quasi-degenerate orbital distribution in developing red TADF emitters.

Influence of Solid Rocket Motor Slag on the Space Debris Environment

The resulting slag particles from solid rocket motor( SRM) firings are an important component of space debris environment. Slag sizes as large as 1 cm have been witnessed in ground tests,and comparable sizes have been also estimated via observations of sub-orbital tail-off events. We achieve slag initial data based on MASTER slag model and SRM historical launch data,and propagate slag long-term orbital evolution taking into account the zonal harmonics J2,atmospheric drag,solar radiation pressure and luni-solar attraction to discuss the slag size distribution and orbital characteristics. Finally,future slag debris environment is evaluated based on two different launch rate assumptions. The result shows that current launch frequency will make the slag population sustain growth and the population will not decrease at once even if there are no more launches in the future.

On the distinct reactivity of two isomers of[IrC_(4)H_(2)]^(+)toward methane and water

The gas-phase reactions of[IrC_(4)H_(2)]^(+)with methane and water have been explored by using mass spectrometry combined with quantum chemical calculations.Interestingly,under the employed conditions,two isomers of[IrC_(4)H_(2)]^(+)co-exist with different reactivity.One of them only activates methane while the other is solely reactive with water to produce CO.Apparently,upon varying the coordination patterns,the Ir center gains rather distinct capabilities of mediating the bond breaking and making processes.The reactivity toward methane mainly depends on the orbital orientation,while the π-aromaticity of the reaction complex matters for the conversion of water.The experimental and theoretical findings in this work not only imply the promising role the Ir atom can play in the bulk-system methane conversion,but may also be instructive on how to construct a highperformance center for steam reforming of methane.