The propeller-like conformation of tetraphenylethylene (TPE) with aggregation-induced emission (AIE) effect was partially and completely fixed by intramolecular cyclization for the first time. The immobilization of propeller-like conformation was found to show great advantages in determining the enantiomer purity, identifying the chiral amines. The completely fixed conformers are resolved into M- and P-enantiomer, which showed mirror imaged CD and almost quantitative fluorescence quantum yield. Furthermore, it also showed a mirror and large circularly polarized luminescence dissymmetric factor, depending on the helicity of the enantiomer. The result provides the most direct and persuasive evidence for AIE via the restriction of intramolecular rotation and finds the new insight of the compounds in chiroptical property.
Benefiting from the high electrochemical surface area brought by 2D nanosheet structure, MoS2 has received great research attention for hydrogen evolution reaction (HER). Recently it has demonstrated that by constructing...
This paper reports that cis-TPE dicycles emit strong fluorescence, while the gem dicycles show almost no emission in solution, demonstrating that the free rotation restriction of the double bond at the excited state is the key factor for AIE effects.
Single-atom catalysts (SACs) have attracted increasing research interests owing to their unique electronic structures, quantum size effects and maximum utilization rate of atoms. Metal organic frameworks (MOFs) are good candidates to prepare SACs owing to the atomically dispersed metal nodes in MOFs and abundant N and C species to stabilize the single atoms. In addition, the distance of adjacent metal atoms can be turned by adjusting the size of ligands and adding volatile metal centers to promote the formation of isolated metal atoms. Moreover, the diverse metal centers in MOFs can promote the preparation of dual-atom catalysts (DACs) to improve the metal loading and optimize the electronic structures of the catalysts. The applications of MOFs derived SACs and DACs for electrocatalysis, including oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, carbon dioxide reduction reaction and nitrogen reduction reaction are systematically summarized in this Review. The corresponding synthesis strategies, atomic structures and electrocatalytic performances of the catalysts are discussed to provide a deep understanding of MOFs-based atomic electrocatalysts. The catalytic mechanisms of the catalysts are presented, and the crucial challenges and perspectives are proposed to promote further design and applications of atomic electrocatalysts.
Improving
the self-conductivity and structural stability of electrode
materials is a key strategy to improve the energy density, rate performance,
and cycle life of supercapacitors. Controlled intercalation of ethyl
carbamate (CH3CH2OCONH2) as the rivet
between Ni–Co hydroxide layers can be used to obtain sufficient
ion transport channels and robust structural stability of hydrangea-like
α-Ni1/3Co2/3(OH)2 (NC). Combining
the improved electronic conductivity offered by the coexistence of
Ni2+ and Co2+ optimizing itself electronic conductivity
and the addition of carbon nanotubes (CNTs) as the electron transport
bridge between the active material and the current collector and the
large specific surface area (296 m2 g–1) reducing the concentration polarization, the capacitance retention
ratio of NC-CNT from 0.2 to 20 A g–1 is up to 93.4%
and its specific capacitance is as high as 1228.7 F g–1 at 20 A g–1. The large total hole volume (0.40
cm3 g–1) and wide crystal plane spacing
(0.71 nm) provide an adequate space to withstand structure deformation
during charge/discharge processes and enhance the structural stability
of the NC material. The capacitance fading ratio of NC-CNT is only
4.5% at 10 A g–1 for 10 000 cycles. The aqueous
supercapacitor (NC-CNT//AC) and all-solid-state supercapacitor (PVA-NC-CNT//PVA-AC)
exhibit high energy density (35.2 W h kg–1 at 100.0
W kg–1 and 35.4 W h kg–1 at 100.7
W kg–1), ultrahigh rate performance (the specific
capacitances at 20 A g–1 are 92.8 and 87.2% compared
to that at 0.5 A g–1), and long cycling life span
(the specific capacitances after 100 000 cycles at 10 A g–1 are 91.5 and 90.8% compared with that of their initial
specific capacitances), respectively. Therefore, hydrangea-like NC
could be a promising material for advanced next-generation supercapacitors.
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