A Small-Molecule Organic Cathode with Extended Conjugation toward Enhancing Na+ Migration Kinetics for Advanced Sodium-Ion Batteries

Organic cathode materials show excellent prospects for sodium-ion batteries (SIBs) owing to their high theoretical capacity. However, the high solubility and low electrical conductivity of organic compounds result in inferior cycle stability and rate performance. Herein, an extended conjugated organic small molecule is reported that combines electroactive quinone with piperazine by the structural designability of organic materials, 2,3,7,8-tetraamino-5,10-dihydrophenazine-1,4,6,9-tetraone (TDT). Through intermolecular condensation reaction, many redox-active groups C═O and extended conjugated structures are introduced without sacrificing the specific capacity, which ensures the high capacity of the electrode and enhances rate performance. The abundant NH2 groups can form intermolecular hydrogen bonds with the C═O groups to enhance the intermolecular interactions, resulting in lower solubility and higher stability. The TDT cathode delivers a high initial capacity of 293 mAh g-1 at 500 mA g-1 and maintains 90 mAh g-1 at an extremely high current density of 70 A g-1. The TDT || Na-intercalated hard carbon (Na-HC) full cells provide an average capacity of 210 mAh g-1 during 100 cycles at 500 mA g-1 and deliver a capacity of 120 mAh g-1 at 8 A g-1.

Dual electronic effects achieving a high-performance Ni(II) pincer catalyst for CO(2) photoreduction in a noble-metal-free system

A carbazolide-bis(NHC) Ni^II catalyst (1; NHC, N-heterocyclic carbene) for selective CO₂ photoreduction was designed herein by a one-stone-two-birds strategy. The extended π-conjugation and the strong σ/π electron-donation characteristics (two birds) of the carbazolide fragment (one stone) lead to significantly enhanced activity for photoreduction of CO₂ to CO. The turnover number (TON) and turnover frequency (TOF) of 1 were ninefold and eightfold higher than those of the reported pyridinol-bis(NHC) Ni^II complex at the same catalyst concentration using an identical Ir photosensitizer, respectively, with a selectivity of ∼100%. More importantly, an organic dye was applied to displace the Ir photosensitizer to develop a noble-metal-free photocatalytic system, which maintained excellent performance and obtained an outstanding quantum yield of 11.2%. Detailed investigations combining experimental and computational studies revealed the catalytic mechanism, which highlights the potential of the one-stone-two-birds effect.

Double π-Extended Undecabenzo[7]helicene

This work reports the first double π-extended undecabenzo[7]helicene 1, which is a large chiral nanographene, composed of 65 fused rings and 186 conjugated carbon atoms. The molecular identity of 1 has been confirmed by single crystal X-ray diffraction. A wine coloured solution of 1 in dichloromethane absorbs light from ultraviolet to the near infrared, featuring an extremely large molar absorption coefficient of 844 000 M^-1  cm^-1 at 573 nm. Optically pure 1 shows a record high electronic circular dichroism intensity in the visible spectral range (|Δϵ|=1375 M^-1  cm^-1 at 430 nm) known for any discrete polycyclic aromatic hydrocarbon. These unusual photophysical properties of 1 contrast sharply with those of a mono-undecabenzo[7]helicene derivative 2.

The synthesis of lactone-bridged 1,3,5-triphenylbenzene derivatives as pi-expanded coumarin triskelions

Two triply lactone-bridged 1,3,5-triphenylbenzene derivatives with solubilizing moieties have been synthesized in five and six steps from commercially available starting materials. Compounds containing the 1,3,5-triphenylbenzene core with two atom bridges are relatively unknown. This new class of pi-expanded coumarins contain triskelion architectures and X-ray crystallographic studies of one of the triskelions indicates that the 1,3,5-triphenylbenzene core adopts a near-planar geometry. This is the only known example of a two atom-bridged 1,3,5-triphenylbenzene derivative to adopt a planar structure.

Visible-Light-Driven Hydrogen Evolution Using Planarized Conjugated Polymer Photocatalysts

Linear poly(p‐phenylene)s are modestly active UV photocatalysts for hydrogen production in the presence of a sacrificial electron donor. Introduction of planarized fluorene, carbazole, dibenzo[b,d]thiophene or dibenzo[b,d]thiophene sulfone units greatly enhances the H₂ evolution rate. The most active dibenzo[b,d]thiophene sulfone co‐polymer has a UV photocatalytic activity that rivals TiO₂, but is much more active under visible light. The dibenzo[b,d]thiophene sulfone co‐polymer has an apparent quantum yield of 2.3 % at 420 nm, as compared to 0.1 % for platinized commercial pristine carbon nitride.

Single-junction polymer solar cells with over 10% efficiency by a novel two-dimensional donor-acceptor conjugated copolymer

Recent advances in bulk heterojunction (BHJ) polymer solar cell (PSC) performance have resulted from compressing the band gap to enhance the short-circuit current density (JSC) while lowering the highest occupied molecular orbital to increase the open-circuit voltage (VOC) and consequently enhance the power conversion efficiencies (PCEs). However, PCEs of PSCs are still constrained by a low JSC, small VOC, and low fill factor (FF). In this study, we report 10.12% PCE from single-junction PSCs based on a novel two-dimensional (2D) conjugated copolymer. By introduction of conjugated 5-alkylthiophene-2-yl side chains to substitute nonconjugated alkoxy side chains in one-dimensional (1D) poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), a novel 2D donor-acceptor low-band-gap conjugated copolymer, poly[[4,8-bis[(5-ethylhexyl)thienyl]benzo[1,2-b;3,3-b]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7-DT), is developed. 2D PTB7-DT is further systematically investigated by absorption spectroscopy, cyclic voltammetry, charge carrier mobility measurement, thin film morphology, and wide-angle X-ray diffraction and compared with 1D PTB7. In comparison with 1D PTB7, 2D PTB7-DT possesses a narrower band gap, tighter π-π stacking, and higher charge carrier mobility. These results are consistent with the observation from first-principle calculations. Consequently, the single-junction PSCs based on 2D PTB7-DT exhibit a PCE of 10.12% with a high JSC, larger VOC, and high FF in comparison with the PSCs based on 1D PTB7.