We studied crystal structures in a monolayer consisting of anisotropic branched colloidal (nano)octapods. Experimentally, octapods were observed to form a monolayer on a substrate with a square-lattice crystal structure by dropcasting and fast evaporation of solvent. The experimental results were analyzed by Monte Carlo simulations using a hard octapod model consisting of four interpenetrating spherocylinders. We confirmed by means of free-energy calculations that crystal structures with a (binary-lattice) square morphology are indeed thermodynamically stable at high densities. The effect of the pod length-to-diameter ratio on the crystal structures was also considered and we used this to constructed the phase diagram for these hard octapods. In addition to the (binary-lattice) square crystal phase, a rhombic crystal and a hexagonal plastic-crystal (rotator) phase were obtained. Our phase diagram may prove instrumental in guiding future experimental studies. KEYWORDS: Octapods, nanocrystals, quasi-2D, self-assembly, anisotropy, colloids T he study of nanocrystal monolayers offers many opportunities for the creation of new materials with bulk properties that differ substantially from the materials that form by self-assembly in three dimensions. 1,2 This has led to a strong experimental and simulation interest in the behavior of nanocrystals in a (quasi-)2D geometry, that is, three-dimensional (3D) particles confined to a two-dimensional (2D) geometry. For instance, the seemingly simple system consisting of monodisperse hard disks in a 2D plane has sparked intense debate on the nature of the 2D solid−liquid phase transition. 3−6 In addition, experiments and simulations 7−14 showed that rod-and square-shaped convex anisotropic particles display a rich mesophase behavior when confined to a (quasi-)2D geometry.Advances in the synthesis of colloids and nanocrystals have resulted in monodisperse samples consisting of complex particles with anisotropic hard and soft interactions 15−21 and present many possibilities for further development in this field. Moreover, new simulation techniques are available to study the experimentally observed phenomenology for these new particles and to tackle the complex numerical problems such investigations bring about. 22−31 Only recently has the investigation into the phase behavior of anisotropic particles in (quasi-)2D by simulation been extended to the realm of nonconvex particles. 29 However, studying the phase behavior of nonconvex particles under confinement remains challenging due to geometric restrictions and the complex interactions between the particles. 32 Our group recently reported an experimental and simulation study of the hierarchical self-assembly of anisotropic branched colloidal nanocrystals, so-called octapods, into 3D superstructures in the liquid bulk phase. 20 In this Letter, we extend our findings to the formation of monolayers consisting of octapods, which were obtained by a deposition−evaporation procedure. In the experiments, we obtained monolay...

of lithium-ion batteries on a large scale. Therefore, the development of rechargeable batteries with high energy density and reliability would be a priority. One of the most promising candidates is lithiumsulfur (Li-S) batteries, which have great potential for addressing these issues. [5][6][7] The conversion reaction based on the reduction of sulfur to lithium sulfides (Li 2 S) yields a high theoretical capacity of 1675 mAh g −1 (S 8 + 16 Li = 8 Li 2 S). Such a capacity is significantly higher than that of insertion cathode materials such as LiCoO 2 and LiFePO 4 , which deliver capacities below 200 mAh g −1 . The 16-electron electrochemical charge transfer reaction with a working voltage of about 2.2 V allows a specific energy density of 2600 Wh kg −1 for Li-S batteries. With optimal configuration, a practical energy density of 500-600 Wh kg −1 would be achievable when considering additional battery components. [8] Moreover, sulfur possesses the merits of abundant resources, safety, and environmental friendliness. The breakthrough in Li-S batteries will promote the development and application of renewable energy.Despite the great potential for replacing lithium-ion batteries, Li-S batteries still face several critical problems. [9] The principal one is the sluggish conversion kinetics of the sulfur reduction reaction (SRR) during discharging due to the low conductivity of sulfur species and complicated 16-electron conversion Lithium-sulfur batteries are one of the most promising alternatives for advanced battery systems due to the merits of extraordinary theoretical specific energy density, abundant resources, environmental friendliness, and high safety. However, the sluggish sulfur reduction reaction (SRR) kinetics results in poor sulfur utilization, which seriously hampers the electrochemical performance of Li-S batteries. It is critical to reveal the underlying reaction mechanisms and accelerate the SRR kinetics. Herein, the critical issues of SRR in Li-S batteries are reviewed. The conversion mechanisms and reaction pathways of sulfur reduction are initially introduced to give an overview of the SRR. Subsequently, recent advances in catalyst materials that can accelerate the SRR kinetics are summarized in detail, including carbon, metal compounds, metals, and single atoms. Besides, various characterization approaches for SRR are discussed, which can be divided into three categories: electrochemical measurements, spectroscopic techniques, and theoretical calculations. Finally, the conclusion and outlook part gives a summary and proposes several key points for future investigations on the mechanisms of the SRR and catalyst activities. This review can provide cutting-edge insights into the SRR in Li-S batteries.

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We report the synthesis and characterization of a novel, stable and blue heteroacene, 2-methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one (BIQ 3). BIQ 3, with its relatively small π framework, has an absorption λ(max) at 620 nm, which is larger than that of pentacene (λ(max) = 582 nm), but BIQ 3 is more stable. The solutions of BIQ 3 are observed without any noticeable photobleaching on the order of days. In the solid state, it is very stable at ambient conditions and can be stored indefinitely. Owing to its pyridone end unit, BIQ 3 can display different resonance structures in different solvents (aprotic and protic) or Lewis acids to give different colors. The attractive stability exhibited by BIQ 3 is very desirable in organic semiconductor devices. Herein, we investigated a simple heterojunction photovoltaic device based on BIQ 3 as an electron donor and [6,6]-phenyl-C(61) butyric methyl ester as an electron acceptor. Our results show that this type of heteroacene could be a good candidate as a charge-transport material in organic semiconductor devices.