New electron-donating segment to develop thermally activated delayed fluorescence emitters for efficient solution-processed non-doped organic light-emitting diodes

Thermally activated delayed fluorescent(TADF) materials capable of efficient solution-processed nondoped organic light-emitting diodes(OLEDs) are of important and practical significance for further development of OLEDs. In this work, a new electron-donating segment, 2,7-di(9 H-carbazol-9-yl)-9,9-dimethyl-9,10-dihydroacridine(2 Cz-DMAC), was designed to develop solution-processable non-doped TADF emitters. 2 Cz-DMAC can not only simultaneously increase the solubility of compounds and suppress harmful aggregation-caused quenching, but also efficiently broaden the delocalization of the highest occupied molecular orbital and promote the reverse intersystem crossing process. Three new TADF emitters, 2-(2,7-di(9 H-carbazol-9-yl)-9,9-dimethylacridin-10(9 H)-yl)dibenzo[b,d]thiophene 5,5-dioxide(2 Cz-DMAC-BTB), 2-(2,7-di(9 H-carbazol-9-yl)-9,9-dimethylacridin-10(9 H)-yl)-9 H-thioxanthen-9-one(2 Cz-DMAC-TXO), 2-(2,7-di(9 H-carbazol-9-yl)-9,9-dimethylacridin-10(9 H)-yl)thianthrene 5,5,10,10-tetraoxide(2 Cz-DMAC-TTR), were developed by using 2 Cz-DMAC segment as the electron-donor. As anticipated, the solution-processed non-doped OLEDs employing 2 Cz-DMAC-BTB, 2 Cz-DMAC-TXO and 2 CzDMAC-TTR as the emitters respectively exhibited green, orange and red emissions with maximum external quantum efficiencies of 14.0%, 6.6% and 2.9%. These results successfully demonstrate the feasibility and convenience of developing efficient solution-processable non-doped TADF emitters based on 2 CzDMAC segment.

The modulation of the discharge plateau of benzoquinone for sodium-ion batteries

p-Benzoquinone(BQ)is a promising candidate for next-generation sodium-ion batteries(SIBs)because of its high theoretical specific capacity,good reaction reversibility,and high resource availability.However,practical application of BQ faces many challenges,such as a low discharge plateau(~2.7 V)as cathode material or a high discharge plateau as anode material compared with inorganic materials for SIBs and high solubility in organic electrolytes,resulting in low power and energy densities.Here,tetrahydroxybenzoquinone tetrasodium salt(Na_(4)C_(6)O_(6))is synthesized through a simple neutralization reaction at low temperatures.The four-ONa electron-donating groups introduced on the structure of BQ greatly lower the discharge plateau by over 1.4 V from ~2.70 V to ~1.26 V,which can change BQ from cathode to anode material for SIBs.At the same time,the addition of four-ONa hydrophilic groups inhibits the dissolution of BQ in the organic electrolyte to a certain extent.As a result,Na_(4)C_(6)O_(6) as the anode displays a moderate discharge capacity and cycling performance at an average work voltage of ~1.26 V versus Na/Na^(+).When evaluated as a Na-ion full cell(NIFC),a Na_(3)V_(2)(PO_(4))_(3)||Na_(4)C_(6)O_(6) NIFC reveals a moderate discharge capacity and an average discharge plateau of ~1.4 V.This research offers a new molecular structure design strategy for reducing the discharge plateau and simultaneously restraining the dissolution of organic electrode materials.

Quantification of the redox properties of microplastics and their effect on arsenite oxidation

Microplastics have attracted global concern.The environmental-weathering processes control their fate,transport,transformation,and toxicity to wildlife and human health,but their impacts on biogeochemical redox processes remain largely unknown.Herein,multiple spectroscopic and electrochemical approaches in concert with wet-chemistry analyses were employed to characterize the redox properties of weathered microplastics.The spectroscopic results indicated that weathering of phenol-formaldehyde resins(PFs)by hydrogen peroxide(H2O2)led to a slight decrease in the content of phenol functional groups,accompanied by an increase in semiquinone radicals,quinone,and carboxylic groups.Electrochemical and wet-chemistry quantifications,coupled with microbial-chemical characterizations,demonstrated that the PFs exhibited appreciable electron-donating capacity(0.264-1.15 mmol e-g^(-1))and electron-accepting capacity(0.120-0.300 mmol e-g^(-1)).Specifically,the phenol groups and semiquinone radicals were responsible for the electron-donating capacity,whereas the quinone groups dominated the electron-accepting capacity.The reversible redox peaks in the cyclic voltammograms and the enhanced electron-donating capacity after accepting electrons from microbial reduction demonstrated the reversibility of the electron-donating and-accepting reactions.More importantly,the electron-donating phenol groups and weathering-induced semiquinone radicals were found to mediate the production of H2O2 from oxygen for arsenite oxidation.In addition to the H2O2-weathered PFs,the ozone-aged PF and polystyrene were also found to have electron-donating and arsenite-oxidation capacity.This study reports important redox properties of microplastics and their effect in mediating contaminant transformation.These findings will help to better understand the fate,transformation,and biogeochemical roles of microplastics on element cycling and contaminant fate.

Kinetics of enhanced adsorption by polarization for organic pollutants on activated carbon fiber

The adsorption kinetics for model pollutants on activated carbon fiber(ACF)by polarization was investigated in this work.Kinetics data obtained for the adsorption of these model pollutants at open-circuit,400 mV,and−400 mV polarization were applied to the Lagergren equation,and adsorption rate constants(Ka)were determined.With the anodic polarization of 400 mV,the capacity of sodium phenoxide was increased from 0.0083 mmol/g at open-circuit to 0.18 mmol/g,and a 17-fold enhancement was achieved;however,the capacity of p-nitrophenol was decreased from 2.93 mmol/g at open-circuit to 2.65 mmol/g.With the cathodal polarization of−400 mV,the capacity of aniline was improved from 3.60 mmol/g at open-circuit to 3.88 mmol/g;however,the capacity of sodium dodecylben-zene sulfonate was reduced from 2.20 mmol/g at open-circuit to 1.59 mmol/g.The enhancement for electrosorption changed with dif ferent groups substituting.Anodic polarization enhances the adsorption of benzene with the electron-donating group.But whether anodic or not,cathodal polariza-tion had less effect on the adsorption of electron-accepting aromatic compounds,and decreased the adsorption capacity of benzene-bearing donor-conjugate bridge-acceptor,while increasing its adsorption rate.Electrostatic interaction played a very important role in the electrosorption of ion-pollutants.

Alternating Terpolymers Based on Tunable Bi-donors with Manipulating Energy Levels and Molecular Geometry

Three novel regular acceptor-donorl-acceptor-donor2（A-D1-A-D2） terpolymers were prepared via em-bedding a second donor（D2） unit into the traditional D-A backbone to manipulate the energy levels and moleculargeometry with no complex synthesis or solubility loss. In these A-D1-A-D2 terpolymers, benzodithiophene（BDT, D1）and diketopyrrolopyrrole（DPP, A） were selected as the basic skeleton, and the dithienopyrrole（DTPy）, carbazole（CZ）and fluorine（FL） units with different electron donating ability were chosen as the second donor trait（D2）. The HOMOenergy levels can be effectively modulated by only varying D2 unit because of the push-pull interaction between do-nor and acceptor units. Versus the D-A bipolymer PDPP-BDT, incorporation of the D2 unit into the copolymers candistinctly lower the highest occupied molecular orbital（HOMO） levels to -5.47 eV for PDDPP-BDT-DTPy, -5.38 eVfor PDDPP-BDT-CZ and -5.23 eV for PDDPP-BDT-FL, which shows the strong dependence on electron-donatingability. Density functional theory（DFT） simulation and X-ray diffraction（XRD） measurements also reveal the effectof the D2 units on the molecular geometry of the terpolymers and their molecular packing. Notably, aPDDPP-BDT-DTPy combined with a thiophene ring and forked tail pendant away from the backbone had less back-bone torsion and more compact packing than the other two counterparts. These results demonstrate that embedding asecond donor（D2） unit into the backbone to construct an A-D1-A-D2 structure can be an effective and direct strategyto manipulate the energy levels and molecular geometry and develop organic semiconducting materials.

Tuning the helical twisting power of nematic liquid crystals induced by chiral 1,2-propanediol derivatives using varied substituents

In this study,a novel series of chiral 1,2-propanediol derivatives with different electron-donating and electron-withdrawing groups were synthesized and characterized by FT-IR and ~1H NMR.The helical twisting properties of all the chiral dopants were investigated by doping the chiral dopants into a nematic liquid crystal host（SLC-1717）.The results indicate that the donor-acceptor electron effect have a prominent influence on helical twisting property of the chiral nematic phase induced by the chiral dopants. Introducing electron-withdrawing groups into the terminal ends of chiral 1,2-propanediol can decrease the absolute values of the helical twisting power.In addition,the helix inversion temperatures of the induced chiral nematic phase are variational with the change of terminal groups.