Hexagonal Monolayer Ice without Shared Edges.

When adsorbed on solids, water molecules are usually arranged into a honeycomb hydrogen-bond network. Here we report the discovery of a novel monolayer ice built exclusively from water hexamers but without shared edges, distinct from all conventional ice phases. Water grown on graphite crystalizes into a robust monolayer ice after annealing, attaining an exceedingly high density of 0.134 Å^{-2}. Unlike chemisorbed ice on metal surfaces, the ice monolayer can translate and rotate on graphite terraces and grow across steps, confirming its two-dimensional nature. First-principles calculations identify the monolayer ice structure as a robust self-assembly of closely packed water hexamers without edge sharing, whose stability is maintained by maximizing the number of intralayer hydrogen bonds on inert surfaces.

Chirality switching of the self-assembled CuPc domains induced by electric field.

Chiral switching of the self-assembled domains of CuPc molecules on the Cd(0001) surface has been investigated by means of a low temperature scanning tunneling microscopy (STM). With the coverage increasing, the CuPc molecules show the structural evolutions from an initial gas-like state to a network phase, a square phase, and finally to a compact phase at full monolayer. In the network and square phases, the achiral CuPc molecules reveal both the point chirality and chiral domains. In particular, the chirality of network domain can be switched from one enantiomer to another driven by the electric filed from a STM tip, which can also lead to the lattice rotation of network phase. These results demonstrate that (i) there is strong interaction between the CuPc molecules and STM tip; (ii) the adsorbed CuPc molecules carry considerable net charge or polarizability due to the charge transfer; (iii) the network phase has a low barrier for the interconversion between right- and left-handed domains. Our findings are significant for the understanding and control of the domain's chirality in the self-assembled structures.

Chiral pinwheel clusters lacking local point chirality.

The supramolecular pinwheel cluster is a unique chiral structure with evident handedness. Previous studies reveal that the chiral pinwheels are composed of chiral or achiral molecules with polar groups, which result in strong intermolecular interactions such as hydrogen-bonding or dipole interactions. Herein, it is shown that the simple linear aromatic molecule, pentacene, can be self-assembled into large chiral pinwheel clusters on the semimetal Bi(111) surface, due to enhanced intermolecular interactions. The pentacene pinwheels reveal two levels of organizational chirality: the chiral hexamers resulting from asymmetric shifting along the long molecular axis, and chiral arrangement of six hexamers with a rotor motif. Furthermore, a new relation between the local point chirality and organizational chirality is identified from the pinwheels: the former is not essential for the latter in 2D pinwheel clusters of the pentacene molecule.

Comparative studies of pentacene and perfluoropentacene grown on a Bi(0001) surface.

We report two distinct growth modes of pentacene (PEN) and perfluoropentacene (PFP) films on a Bi(0001) substrate investigated by scanning tunneling microscopy (STM). PEN grows epitaxially on Bi(0001) at room temperature (RT), resulting in the formation of bulk-like crystalline films. In contrast, submonolayer PFP forms a two-dimensional (2D) liquid-like phase with PFP molecules loosely bound on Bi(0001). Beyond one monolayer, the PFP molecules diffuse over very long distances to aggregate into three-dimensional (3D) islands, leading to a rough film morphology. Utilizing the stacking interaction at the PFP/PEN interface, we deposited PFP on the template of an ordered PEN monolayer formed on Bi. It is found that PFP molecules nucleate into ordered crystalline islands with PFP molecules standing-up. The different morphologies of PEN and PFP overlayers can be understood in terms of perfluorination induced decoupling of PFP molecules from the Bi substrate below.

84% efficiency improvement in all-inorganic perovskite light-emitting diodes assisted by a phosphorescent material.

A novel mixed perovskite emitter layer is applied to design all-inorganic cesium lead halide perovskite light-emitting diodes (PeLEDs) with high electroluminescence (EL) performance, by combining CsPbBr3 with iridium(iii)bis[2-(4',6'-difluorophenyl)pyridinato-N,C2']-picolinate (FIrpic), where FIrpic is a phosphorescent material with very high internal quantum efficiency (IQE) approaching 100%. The CsPbBr3:FIrpic PeLEDs show a maximum luminance of 5486 cd m-2, and an external quantum efficiency of 0.47%, which are 1.84 and 1.76 times that of neat CsPbBr3 PeLEDs, respectively. It is found that FIrpic molecules as an assistant dopant can efficiently transmit energy from the excitons of FIrpic to the excited state of the CsPbBr3 emitter via a Förster energy transfer process, leading to enhanced EL efficiency in the CsPbBr3:FIrpic PeLEDs.

Highly Efficient Perovskite Light-Emitting Diodes Incorporating Full Film Coverage and Bipolar Charge Injection.

Solution-processable organometal halide perovskites have been emerging as very promising materials for light-emitting diodes (LEDs) because of their high color purity, low cost, and high photoluminescence quantum yield. However, their electroluminescent performance is still limited by incomplete surface coverage and inefficient charge injection into the perovskite. Here, we demonstrate highly efficient perovskite LEDs (PeLEDs) incorporating full film coverage and bipolar charge injection within the active layer by introducing perovskite precursor poly(9-vinylcarbazole):1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (PVK:TPBi) toluene solution into CH3NH3PbBr3 N,N-dimethylformamide solution. Both the film coverage and the charge injections were simultaneously improved by antisolvent of toluene and PVK:TPBi matrix, respectively. After the film morphology and weight ratio of PVK:TPBi were carefully adjusted, the optimal PeLEDs gave efficient emission with turn-on voltage of ∼2.8 V, maximum luminance of ∼7263 cd/m2, maximum current efficiency of ∼9.45 cd/A, and maximum external quantum efficiency of ∼2.28%, which are among the best results based on MAPbBr3 reported to date.

Nearly 100% Efficiency Enhancement of CH3NH3PbBr3 Perovskite Light-Emitting Diodes by Utilizing Plasmonic Au Nanoparticles.

Organic-inorganic hybrid perovskites have drawn considerable attention due to their great potentials in lighting and displaying. Despite great progress being demonstrated in perovskites light-emitting diodes (PeLEDs), the commercialization of PeLEDs was still limited by their low efficiencies and poor device stabilities. Utilizing the metallic nanoparticles was a feasible way to further improve the efficiencies of PeLEDs. Herein, substantially enhanced electroluminescent performance of CH3NH3PbBr3-based PeLEDs were first demonstrated by incorporating plasmonic gold nanoparticles (Au NPs) into the hole injection layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Compared to the reference device without Au NPs, 109% enhancement in maximum luminance and 97% enhancement in maximum EQE were achieved upon 9 vol % Au NPs doping. Such enhancements can be ascribed to the localized surface plasmon resonance between Au NPs and CH3NH3PbBr3 excitons, as well as the enhanced electrical conductivity of modified PEDOT:PSS. Our studies indicated great potential of Au NPs in developing highly efficient PeLEDs.

Supramolecular Motors on Graphite Surface Stabilized by Charge States and Hydrogen Bonds.

Molecular motors are nanoscale machines that convert external energies into controlled mechanical movements. In supramolecular motors, the rotator and stator are held together mechanically, and thus the rotation can be essentially barrier free when molecular conformation is negligible. However, nearly all the supramolecular motors appeared in solutions or host-guest complexes. Surface-mounted supramolecular motors have rarely been addressed, even though they are easily manipulated by external fields. Here we report a surface-mounted supramolecular motor assembled by charge states and hydrogen bonds. On a graphite surface, individual ethanol clusters can be charged with a scanning tunneling microscopy tip and then trap the ethanol chains with a permanent dipole moment. Serving as a rotator, the trapped ethanol chains rotate around a charged cluster driven by the inelastic tunneling electrons. Random rotation in clockwise or anticlockwise direction occurs in the chiral molecular chains through chiral flipping. Directional rotation with clockwise chirality can be realized by introducing a chiral branch to the near end of ethanol chains to suppress the chiral flipping with steric hindrance.

Luminescent golden silk and fabric through in situ chemically coating pristine-silk with gold nanoclusters.

Silk is an excellent natural material and has been used for a variety of applications. Modification of the pristine silk is usually needed depending on the intended purpose. The technical treatments involved in the modification not only should be easy, rapid, environmentally friendly, and cheap but should also retain the features of the pristine silk. Herein, we demonstrate that luminescent silk and fabric can be produced through nanotechnology. The surface of the natural silk fiber is chemically coated with luminescent gold nanoclusters (AuNCs) composed of tens to hundreds of Au atoms through a redox reaction between the protein-based silk and an Au salt precursor. The luminescent silk coated with AuNCs (called golden silk) possesses good optical properties, including a relatively long wavelength emission, high quantum yields, a long fluorescent lifetime, and photostability. Moreover, golden silk prepared this way has better mechanical properties than pristine silk, is better able to inhibit UV, and has lower toxicity in vitro. This work not only provides an effective strategy for in situ preparation of luminescent metal nanoclusters on a solid substrate but also paves the way for large-scale and industrialized production of novel silk-based materials or fabrics through nanotechnology.

Rapid synthesis of highly luminescent and stable Au20 nanoclusters for active tumor-targeted imaging in vitro and in vivo.

Rapid synthesis of protein-stabilized Au20 nanoclusters (Au20NCs) with high fluorescence quantum yield (QY) up to ∼15% is successfully achieved by manipulating the reaction kinetics. The as-obtained Au20NCs, identified by mass spectrometry, have an average size of 2.6 nm, with strong fluorescence emission at 620 nm (2.00 eV) upon excitation at either 370 nm (3.35 eV) or 470 nm (2.64 eV). The advantages of the as-obtained Au20NCs, including small sizes, high fluorescence QY, excellent photostability, non-toxicity, and good stability in biological media, make them ideal candidates as good luminescent probes for optical imaging in vitro and in vivo. Our results demonstrate that the uptake of Au20NCs by both cancer cells and tumor-bearing nude mice can be improved by receptor-mediated internalization, compared with that by passive targeting. Because of their selective accumulation at the tumor sites, the Au20NC probes can be used as potential indicators for cancer diagnosis. This work not only provides a new understanding of the rapid synthesis of highly luminescent Au20NCs but also demonstrates that the functionalized-Au20NCs are excellent probes for active tumor-targeted imaging in vitro and in vivo.

Highly selective detection of bacterial alarmone ppGpp with an off-on fluorescent probe of copper-mediated silver nanoclusters.

In this study, a facile strategy for highly selective and sensitive detection of bacterial alarmone, ppGpp, which is generated when bacteria face stress circumstances such as nutritional deprivation, has been established by developing an off-on fluorescent probe of Cu(2+)-mediated silver nanoclusters (Ag NCs). This work not only achieves highly selective detection of ppGpp in a broad range concentration of 2-200 µM, but also improves our understanding of the specific recognitions among DNA-Ag NCs, Cu(2+), and ppGpp. The present strategy, together with other reports on the Ag NCs-related analytical methods, has also identified that Ag NCs functionalized with different molecules on their surfaces can be engineered fluorescent probes for a wide range of applications such as biosensing and bioimaging.

Highly selective and sensitive detection of coralyne based on the binding chemistry of aptamer and graphene oxide.

In this contribution, an organic small molecule (OSM)-participating interaction between its aptamer and graphene oxide (GO) is investigated by taking coralyne as an example. Based on their interactions, a simple, rapid, highly sensitive and selective fluorometric method for the detection of coralyne is developed. GO can effectively quench the fluorescence of dye-labeled aptamer, while stronger binding of the aptamer and its target can make the fluorescence be recovered, which have been well demonstrated by the studies of the fluorescence spectra, fluorescence anisotropy, and circular dichroism spectra. In this case, the coralyne can be quantificationally detected by the variation of the fluorescence intensity, where GO acts as an efficient signal-to-background enhancer. With the increase of the coralyne, the fluorescence intensity increases gradually and linearly proportional to the concentration of the coralyne in the range of 10-700 nmol L(-1). This method is reliable, and has been successfully applied for the detection of coralyne in complicated matrixes.