As a fundamental property of light, the angular momentum of photons has been of great interest. Here, we demonstrate that optical spin-to-orbital angular momentum conversion can occur in a homogeneous and isotropic medium. This Letter presents both theoretical and experimental studies of this conversion in a tightly focused beam and shows that the orbital rotation speeds of trapped particles are altered because of this conversion as predicted by theory.

The synthesis of fully conjugated sp 2 -carbon covalent organic frameworks (COF) is extremely challenging given the difficulty of the formation of very stable carbon-carbon double bonds (-C=C-). Here,w er eport the successful preparation of a2 DC OF (TP-COF) based on triazine as central planar units bridged by sp 2 -carbon linkers through the -C = Ccondensation reaction. High-resolution-transmission electron microscopy( HRTEM) clearly confirmed the tessellated hexagonal pore structure with ap ore center-to-center distance of 2nm. Powder X-rayd iffraction (PXRD) together with structural simulations revealed an AA stacking mode of the obtained layered structure.T P-COF turned out to be an excellent semiconductor material with aL UMO energy of À3.23 eV and aband gap of 2.36 eV.Excitingly,this novel sp 2carbon conjugated TP-COF exhibited unprecedented coenzyme regeneration efficiency and can significantly boost the coenzyme-assisted synthesis of l-glutamate to arecord-breaking 97 %yield within 12 minutes.Long-range p-conjugated two-dimensional (2D) materials have received considerable attention in recent years and present ar ange of unique advantages over traditional polymeric materials. [1][2][3][4][5][6][7] In particular, the topological arrangement of aromatic units propagating in two spatial directions equips them with superior (photo-)electronic and magnetic properties. [8][9][10] However,t he delicate control over specific arrangements of functional units to obtain highly ordered 2D materials is still ag reat challenge. [11][12][13][14] Covalent organic frameworks (COFs) take advantage of the structural selfhealing properties stemming from dynamic covalent bond formation. [15][16][17][18][19][20][21] This advancement has made it possible to synthesize well-defined 2D structures with diverse functionalities.A mong all synthetic strategies of COFs,t he most frequently used dynamic covalent-bond-formations trategies are the Schiff base condensation reaction and the boronate ester bond formation. Despite the fact that the extended pconjugation can propagate through the -N = C-double bonds in the Schiff base structure,t he imine-linkage displays relatively poor stability and weak electron delocalization. To overcome this limitation, researchers have been actively exploring new reactions to construct fully conjugated COFs with an optimal electron delocalization. [22][23][24][25][26][27][28] However,examples of fully conjugated imine-free COFs with sp 2 -carbon double bond structures are still rare because it is extremely difficult to form -C = C-bonds via reversible coupling reactions and simultaneously gain the desired conjugation as well as the refined crystallinity within the COF structure.Recently, Jiang et al. and Feng et al. successfully constructed conjugated 2D COFs bearing -C = C-linkage by using Knoevenagel polycondensation. [29][30][31][32] Ther eported sp 2 -carbon linked 2D COFs were demonstrated to have excellent electrochemical and charge-transfer properties.Thee nhanced electron delocalization of sp 2...

The conclusion is inevitable: Increasing stabilization of an anionic transition state with increasing π-acidity of the catalyst is observed; thus, anion-π interactions can contribute to catalysis.

The introduction of new noncovalent interactions to build functional systems is of fundamental importance. We here report experimental and theoretical evidence that anion−π interactions can contribute to catalysis. The Kemp elimination is used as a classical tool to discover conceptually innovative catalysts for reactions with anionic transition states. For anion−π catalysis, a carboxylate base and a solubilizer are covalently attached to the π-acidic surface of naphthalenediimides. On these π-acidic surfaces, transition-state stabilizations up to ΔΔGTS = 31.8 ± 0.4 kJ mol–1 are found. This value corresponds to a transition-state recognition of KTS = 2.7 ± 0.5 μM and a catalytic proficiency of 3.8 × 105 M–1. Significantly increasing transition-state stabilization with increasing π-acidity of the catalyst, observed for two separate series, demonstrates the existence of “anion−π catalysis.” In sharp contrast, increasing π-acidity of the best naphthalenediimide catalysts does not influence the more than 12 000-times weaker substrate recognition (KM = 34.5 ± 1.6 μM). Together with the disappearance of Michaelis–Menten kinetics on the expanded π-surfaces of perylenediimides, this finding supports that contributions from π–π interactions are not very important for anion−π catalysis. The linker between the π-acidic surface and the carboxylate base strongly influences activity. Insufficient length and flexibility cause incompatibility with saturation kinetics. Moreover, preorganizing linkers do not improve catalysis much, suggesting that the ideal positioning of the carboxylate base on the π-acidic surface is achieved by intramolecular anion−π interactions rather than by an optimized structure of the linker. Computational simulations are in excellent agreement with experimental results. They confirm, inter alia, that the stabilization of the anionic transition states (but not the neutral ground states) increases with the π-acidity of the catalysts, i.e., the existence of anion−π catalysis. Preliminary results on the general significance of anion−π catalysis beyond the Kemp elimination are briefly discussed

Highly conjugated three-dimensional covalent organic frameworks (3D COFs) were constructed based on spirobifluorene cores linked via imine bonds (SP-3D-COFs) with novel interlacing conjugation systems. The crystalline structures were confirmed by powder X-ray diffraction and detailed structural simulation. A 6-or 7-fold interpenetration was formed depending on the structure of the linking units. The obtained SP-3D-COFs showed permanent porosity and high thermal stability. In application for solar cells, simple bulk doping of SP-3D-COFs to the perovskite solar cells (PSCs) substantially improved the average power conversion efficiency by 15.9% for SP-3D-COF 1 and 18.0% for SP-3D-COF 2 as compared to the reference undoped PSC, while offering excellent leakage prevention in the meantime. By aid of both experimental and computational studies, a possible photoresponsive perovskite−SP-3D-COFs interaction mechanism was proposed to explain the improvement of PSC performance after SP-3D-COFs doping.

SummaryAtomic catalysts are promising alternatives to bulk catalysts for the hydrogen evolution reaction (HER), because of their high atomic efficiencies, catalytic activities, and selectivities. Here, we report the ultrathin nanosheet of graphdiyne (GDY)-supported zero-valent palladium atoms and its direct application as a three-dimensional flexible hydrogen-evolving cathode. Our theoretical and experimental findings verified the successful anchoring of Pd0 to GDY and the excellent catalytic performance of Pd0/GDY. At a very low mass loading (0.2%: 1/100 of the 20 wt % Pt/C), Pd0/GDY required only 55 mV to reach 10 mA cm−2 (smaller than 20 wt % Pt/C); it showed larger mass activity (61.5 A mgmetal−1) and turnover frequency (16.7 s−1) than 20 wt % Pt/C and long-term stability during 72 hr of continuous electrolysis. The unusual electrocatalytic properties of Pd0/GDY originate from its unique and precise structure and valence state, resulting in reliable performance as an HER catalyst.

The tortoise and the hare: anion–π interactions are reported to selectively accelerate the intrinsically disfavored addition of malonate half thioesters.

It is of great urgency to develop efficient, cost-effective, stable and industrially applicable electrocatalysts for renewable energy systems. But there are still few candidate materials. Here we show a bifunctional electrocatalyst, comprising graphdiyne-exfoliated and -sandwiched iron/cobalt layered double-hydroxide nanosheet arrays grown on nickel foam, for the oxygen and hydrogen evolution reactions. Theoretical and experimental data revealed that the charge transport kinetics of the structure were superior to iron/cobalt layered double-hydroxide, a prerequisite for improved electrocatalytic performance. The incorporation with graphdiyne increased the number of catalytically active sites and prevented corrosion, leading to greatly enhanced electrocatalytic activity and stability for oxygen evolution reaction, hydrogen evolution reaction, as well as overall water splitting. Our results suggest that the use of graphdiyne might open up new pathways for the design and fabrication of earth-abundant, efficient, functional, and smart electrode materials with practical applications.